arXiv:0704.1244v1  [astro-ph]  10 Apr 2007
Astronomy & Astrophysics manuscript no. m6020 c© ESO 2018
September 20, 2018
SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
V. Stanishev1 ,⋆, A. Goobar1, S. Benetti2, R. Kotak3,4, G. Pignata5, H. Navasardyan2 , P. Mazzali6,7, R. Amanullah1, G.
Garavini1, S. Nobili1, Y. Qiu8, N. Elias-Rosa2,9, P. Ruiz-Lapuente10 , J. Mendez10,11, P. Meikle12, F. Patat3, A.
Pastorello6,4, G. Altavilla10, M. Gustafsson13 , A. Harutyunyan2 , T. Iijima2, P. Jakobsson14 , M.V. Kichizhieva15, P.
Lundqvist16, S. Mattila12, J. Melinder16, E.P. Pavlenko17, N.N. Pavlyuk18, J. Sollerman16,14, D.Yu. Tsvetkov18, M.
Turatto2, W. Hillebrandt7
1 Physics Department, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
2 INAF, Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, 35122 Padova, Italy
3 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
4 Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, BT7 1NN, UK
5 Departamento de Astronomı́a y Astrofı́sica, Pontificia Universidad Católica de Chile, Campus San Joaquı́n. Vicuña Mackenna
4860 Casilla 306, Santiago 22, Chile
6 INAF Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34131 Trieste, Italy
7 Max-Planck-Institut für Astrophysik, PO Box 1317, 85741 Garching, Germany
8 National Astronomical Observatories, Chinese Academy of Sciences, 100012 Beijing, China
9 Universidad de La Laguna, Av Astrofı́sico Fransisco Sánchez s/n, E-38206. La Laguna, Tenerife, Spain
10 Department of Astronomy, University of Barcelona, Marti i Franques 1, E-08028 Barcelona, Spain
11 Isaac Newton Group of Telescopes, Apartado de correos 321, E-38700 Santa Cruz de La Palma, Canary Islands, Spain
12 Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London, SW7 2AZ, UK
13 Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark
14 Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø,
Denmark
15 Tavrida State University, Simferopol, Ukraine
16 Department of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
17 Crimean Astrophysical Observatory, Ukraine
18 Sternberg Astronomical Institute, Moscow State University, Universitetskii pr. 13, Moscow 119992, Russia
Received ;accepted
ABSTRACT
Aims. We present a study of the optical and near-infrared (NIR) properties of the Type Ia Supernova (SN Ia) 2003du.
Methods. An extensive set of optical and NIR photometry and low-resolution long-slit spectra was obtained using a number of
facilities. The observations started 13 days before B-band maximum light and continued for 480 days with exceptionally good time
sampling. The optical photometry was calibrated through the S-correction technique.
Results. The UBVRIJHK light curves and the color indices of SN 2003du closely resemble those of normal SNe Ia. SN 2003du
reached a B-band maximum of 13.49±0.02 mag on JD2452766.38 ±0.5. We derive a B-band stretch parameter of 0.988±0.003,
which corresponds to ∆m15 = 1.02 ± 0.05, indicative of a SN Ia of standard luminosity. The reddening in the host galaxy was
estimated by three methods, and was consistently found to be negligible. Using an updated calibration of the V and JHK absolute
magnitudes of SNe Ia, we find a distance modulus µ = 32.79 ± 0.15 mag to the host galaxy, UGC 9391. We measure a peak uvoir
bolometric luminosity of 1.35(±0.20) × 1043 erg s−1 and Arnett’s rule implies that M56Ni ≃ 0.68 ± 0.14 M⊙ of
56Ni was synthesized
during the explosion. Modeling of the uvoir bolometric light curve also indicates M56Ni in the range 0.6 − 0.8 M⊙. The spectral
evolution of SN 2003du at both optical and NIR wavelengths also closely resembles normal SNe Ia. In particular, the Si ii ratio at
maximum R(Si ii)= 0.22 ± 0.02 and the time evolution of the blueshift velocities of the absorption line minima are typical. The
pre-maximum spectra of SN 2003du showed conspicuous high-velocity features in the Ca ii H&K doublet and infrared triplet, and
possibly in Si ii λ6355, lines. We compare the time evolution of the profiles of these lines with other well-observed SNe Ia and we
suggest that the peculiar pre-maximum evolution of Si ii λ6355 line in many SNe Ia is due to the presence of two blended absorption
components.
Key words. stars: supernovae: general – stars: supernovae: individual: SN 2003du – methods: observational – techniques: photometric
– techniques: spectroscopic
1. Introduction
Type Ia supernovae (SNe Ia) form a relatively homogeneous
class of objects with only a small scatter in their observed ab-
solute peak magnitudes (∼ 0.3 mag). Moreover, their spectra
⋆ E-mail: vall@physto.se
and light curves are strikingly similar (e.g. Branch & Tammann,
1992). Theoretical investigations strongly suggest that SNe Ia
are thermonuclear explosions of carbon/oxygen white dwarfs
(WD) with masses close to the Chandrasekhar limit ∼ 1.4M⊙
(for a review see Hillebrandt & Niemeyer, 2000). In the fa-
vored model, the WD mass grows via accretion from a com-
http://arxiv.org/abs/0704.1244v1
2 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
panion star until the mass reaches the Chandrasekhar limit and
the WD ignites at (or near) its center. The light curves of SNe Ia
are powered by the energy released from the decay of radioac-
tive 56Ni produced during the explosion (typically a few tenths
of M⊙) and its daughter nuclides, and the scatter of the abso-
lute magnitudes is mostly due to the different amounts of syn-
thesized 56Ni. However, it has been shown that the peak lumi-
nosity of SNe Ia correlates with the luminosity decline rate af-
ter maximum light; the slower the decline, the greater the peak
luminosity (Pskovskii, 1977; Phillips, 1993; Hamuy et al., 1995,
1996; Riess et al., 1995). After correcting for the empirical ”light
curve width – peak luminosity” relation and for the extinction
in the host galaxy, the dispersion of the SN Ia absolute peak
B magnitudes is ∼ 0.14 mag (Phillips et al., 1999). This prop-
erty combined with their high intrinsic luminosity (MV ≃ −19.2
mag), make SNe Ia ideal for measuring relative cosmological
distances.
Observations of SNe Ia out to a redshift of z ∼ 1.0 led to
the surprising discovery that the expansion of the Universe is
accelerating, and that ∼ 70% of the Universe consists of an
unknown constituent with effective negative pressure, dubbed
”dark energy” (Riess et al., 1998; Perlmutter et al., 1999; Knop
et al., 2003; Riess et al., 2004; Astier et al., 2006; Riess et al.,
2007; Wood-Vasey et al., 2007). Currently, the favored model
for dark energy is a non-zero positive cosmological constant Λ
(or vacuum energy), but more exotic models have also been pro-
posed (for a review see Peebles & Ratra, 2003). There are sev-
eral observational programs planned or in progress that aim to
discover and observe hundreds of SNe Ia up to z ∼ 1.7, with
the goal of measuring cosmological parameters with greatly im-
proved accuracy. This will enable distinctions to be made be-
tween the large number of proposed models for dark energy.
Although these programs will be able to greatly reduce the sta-
tistical uncertainties on the measured cosmological parameters,
the output will still be limited by systematic errors due to our
poor knowledge of some aspects of SNe Ia and their environ-
ment. Two of the major concerns are the possible evolution of
the brightness or colors of SNe Ia with redshift and the esti-
mation of the reddening in the host galaxy. There are indica-
tions that the amount of 56Ni synthesized during the explosion
is sensitive to the metallicity, carbon-to-oxygen (C/O) ratio and
the central density of the exploding WD (Hoeflich et al., 1998;
Umeda et al., 1999; Timmes et al., 2003; Röpke & Hillebrandt,
2004; Röpke et al., 2006), although based on three-dimensional
simulations Röpke & Hillebrandt (2004) and Röpke et al. (2006)
found that the C/O ratio has little effect on the 56Ni production.
These quantities may, however, evolve with redshift and might
therefore introduce some evolution of the observed SNe Ia prop-
erties. However, our poor knowledge of the details of the physics
of the explosion, the progenitor systems and how the WD mass
grows to the Chandrasekhar limit (e.g., Hillebrandt & Niemeyer,
2000)) prevents us from accurately estimating the magnitude of
the effect, and the extent to which it could affect the derived
cosmological parameters. The difficulties in accurately estimat-
ing the reddening in the SN host galaxies arise mostly from the
uncertainty in the intrinsic colors of SNe Ia (e.g., Nobili et al.,
2003) and the calibration of the photometry (Suntzeff, 2000),
combined with poor knowledge of the dust properties.
In this paper we present observations of the nearby Type
Ia SN 2003du. It was discovered by The Lick Observatory
and Tenagra Observatory Supernova Searches (Schwartz &
Holvorcem, 2003) in the nearby (recession velocity of 1914
km s−1) SBd galaxy UGC 9391 on 2003 April 22.4 UT. Kotak
et al. (2003) classified SN 2003du as a normal SN Ia at about
two weeks before maximum light and an intensive optical and
NIR observational campaign was initiated by the European
Supernova Collaboration (ESC). The optical and NIR observa-
tions were carried out until 466 and 30 days after B-band max-
imum light, respectively; throughout this paper we define the
phase of the supernova as the time in days from the B-band
maximum. The goal of the ESC is to make progress in our un-
derstanding of the physics of the thermonuclear SN explosions
by collecting and analyzing early-time observations of nearby
SNe Ia. Since 2002 the ESC has obtained via coordinated obser-
vations using a large number of telescopes optical and IR ob-
servations for 15 nearby SNe Ia. First results of the observations
have already been published (SN 2002bo – Benetti et al. 2004,
Stehle et al. 2005; SN 2002dj – Pignata et al. 2005; SN 2002er –
Pignata et al. 2004, Kotak et al. 2005; SN 2003cg – Elias-Rosa
et al. 2006; SN 2004eo – Pastorello et al. 2007a; SN 2005cf –
Pastorello et al. 2007b, Garavini et al. 2007; Benetti et al. 2005;
Mazzali et al. 2005a). Optical observations of SN 2003du have
also been presented by Gerardy et al. (2004), Anupama et al.
(2005) and Leonard et al. (2005).
2. Observations and data reduction
2.1. Optical spectroscopy
The optical spectroscopy log of SN 2003du is given in Table 1.
The spectra were reduced1 following the algorithm of (Horne,
1986). The images were first bias and flat-field corrected. The
1D spectra were then optimally extracted from the 2D images,
simultaneously identifying and removing the cosmic rays and
bad pixels. The spectra were wavelength calibrated using arc-
lamp spectra. The wavelength calibration was checked against
the night-sky emission lines and, when necessary, small addi-
tive corrections were applied. Spectrophotometric standard stars
were used to flux calibrate the SN spectra. Telluric absorp-
tion features were removed from the supernova spectra follow-
ing Wade & Horne (1988). On a number of nights two differ-
ent spectrometer settings were used to cover the whole optical
wavelength range, and the two spectra were combined into a
single spectrum. Most of the spectra have dispersion between
∼ 1 Å pixel−1 and ∼ 5 Å pixel−1, except for the few red spec-
tra taken at Asiago 1.82m telescope, which have a dispersion of
∼ 15 Å pixel−1 and one WHT spectrum with ∼ 0.23 Å pixel−1.
The spectra were obtained with the slit oriented along the
parallactic angle in order to minimize differential losses due to
atmospheric refraction (Filippenko, 1982). Nevertheless the rel-
ative flux calibration was not always sufficiently accurate and
the final flux calibration was achieved by slightly correcting the
spectra to match the observed photometry. This step was done
alongside the calibration of the photometry and is discussed in
detail in the Appendix.
2.2. Optical photometry
The optical photometric observations of SN 2003du were ob-
tained with a number of instruments equipped with broadband
UBVRI filters. The CCD images were bias and flat-field cor-
rected. Cosmic ray hits were identified and cleaned with the
1 All data reduction and calibration was done in IRAF and with
our own programs written in IDL. IRAF is distributed by the
National Optical Astronomy Observatories, which are operated by the
Association of Universities for Research in Astronomy, Inc., under co-
operative agreement with the National Science Foundation.
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 3
Table 1. Log of the optical spectroscopy
Date (UT) JD Phase Wavelength Telescopea
[day] range [Å]
2003 Apr 23 2452753.58 −12.8 4900-7500 INT
2003 Apr 25 2452755.43 −10.9 3450-10400 AS1.8
2003 Apr 25 2452755.58 −10.8 4250-7500 NOT
2003 Apr 28 2452758.54 −7.8 3200-7500 INT
2003 Apr 30 2452760.56 −5.8 3230-8060 TNG
2003 May 02 2452762.39 −4.0 3230-8060 TNG
2003 May 04 2452764.48 −1.9 3436-7776 AS1.8
2003 May 05 2452765.39 −1.0 3500-7776 AS1.8
2003 May 06 2452766.39 +0.0 3447-7776 AS1.8
2003 May 07 2452767.55 +1.2 3500-9590 AS1.8
2003 May 08 2452768.54 +2.2 5860-7060 AS1.2
2003 May 09 2452769.54 +3.2 3500-10010 AS1.8
2003 May 10 2452770.64 +4.3 3300-10000 CA2.2
2003 May 12 2452772.57 +6.2 4680-7017 AS1.2
2003 May 13 2452773.61 +7.2 3300-7200 NOT
2003 May 14 2452774.59 +8.2 3300-7200 NOT
2003 May 15 2452775.48 +9.1 3250-7200 NOT
2003 May 16 2452776.47 +10.0 3260-9800 NOT
2003 May 21 2452781.51 +15.1 3800-6130 AS1.2
2003 May 23 2452783.55 +17.2 3600-10100 AS1.8
2003 May 24 2452784.60 +18.2 4260-6595 AS1.2
2003 May 25 2452785.39 +19.0 3700-7776 AS1.8
2003 May 27 2452787.52 +21.1 3400-8830 CA2.2
2003 Jun 01 2452792.52 +26.1 3240-8060 TNG
2003 Jun 06 2452797.60 +31.2 3240-8060 TNG
2003 Jun 09 2452800.45 +34.1 3500-9500 WHT
2003 Jun 14 2452805.38 +39.0 3700-10000 WHT
2003 Jun 20 2452811.54 +45.2 3880-7770 AS1.8
2003 Jun 26 2452817.52 +51.1 3350-10000 WHT
2003 Jul 08 2452829.44 +63.1 3700-9850 NOT
2003 Jul 17 2452838.41 +72.0 3500-10000 WHT
2003 Jul 29 2452850.42 +84.0 3600-10000 WHT
2003 Aug 23 2452875.32 +108.9 3000-7820 AS1.8
2003 Sep 25 2452907.82 +141.4 3500-8800 CA2.2
2003 Nov 18 2452962.25 +195.9 4370-7050 WHTb
2003 Dec 01 2452975.70 +209.3 3000-7600 CA3.5
2003 Dec 13 2452987.72 +221.3 3500-8820 CA2.2
2004 Feb 02 2453038.71 +272.3 3800-8000 CA3.5
2004 May 17 2453143.30 +376.9 3500-8060 TNG
a AS1.8 = Asiago 1.82m + AFOSC; AS1.2 = Asiago 1.22m + B&C;
TNG = TNG 3.58m + DOLORES; NOT = NOT 2.6m + ALFOSC;
CA2.2 = Calar Alto 2.2m + CAFOS; CA3.5 = Calar Alto 3.5m +
MOSCA; WHT =WHT 4.2m + ISIS; INT = INT 2.5m + IDS
b average of spectra obtained on 17 and 18 Nov. 2003; these spec-
tra cover the ranges 4370–5220 Å and 6200–7050 Å with dispersion
0.23 Å pixel−1.
Laplacian detection algorithm of van Dokkum (2001). The ob-
servations consist of single exposures at early times and dithered
multiple exposures at late epochs. In the latter case, the images
in each filter were combined to form a single image. For the I-
band, we also corrected for fringing in the individual exposures.
The SN lies only 15′′ from the host galaxy nucleus, on a
complex background (Fig. 1). The background contamination
may significantly degrade the photometry, especially at late
epochs when the SN has faded considerably. The approach com-
monly used is to subtract the background using template galaxy
images without the SN, taken either before or a few years af-
ter the SN explosion. The galaxy template, preferably with bet-
ter seeing and signal-to-noise ratio (S/N) than the SN images, is
aligned with the SN image, convolved with a suitable kernel so
that the point-spread functions (PSF) of the two images are the
same, then scaled to match the flux level of the SN image and
Fig. 1. A B-band finding chart of SN 2003du with the comparison stars
labeled by numbers. The image was obtained 87 days after B-band max-
imum.
Table 2. Calibrated magnitudes of the local stars around SN 2003du.
The number in parentheses are the uncertainties in mmag.
Star U B V R I
1 13.864 (39) 13.848 (22) 13.309 (13) 12.960 (13) · · ·
2 15.004 (39) 14.920 (22) 14.310 (14) 13.911 (13) 13.624 (12)
3 16.562 (40) 16.428 (22) 15.792 (13) 15.400 (13) 15.077 (13)
4 16.930 (40) 17.024 (23) 16.462 (14) 16.113 (14) 15.792 (12)
5 18.261 (45) 17.611 (24) 16.251 (14) 15.258 (15) 14.117 (13)
6 18.254 (45) 17.909 (24) 17.011 (15) 16.478 (14) 16.012 (12)
7 17.660 (42) 17.552 (23) 16.893 (14) 16.468 (14) 16.129 (12)
8 17.114 (40) 16.993 (23) 16.307 (15) 15.829 (14) 15.504 (12)
9 17.806 (42) 17.951 (24) 17.518 (15) 17.179 (16) 16.875 (13)
10 17.809 (42) 18.092 (24) 17.675 (16) 17.357 (16) 17.057 (13)
11 17.775 (42) 17.586 (23) 16.874 (15) 16.418 (15) 16.107 (14)
12 18.328 (46) 18.636 (27) 18.158 (18) 17.799 (18) 17.487 (14)
subtracted. The SN flux can then be correctly measured on the
background-subtracted image.
Lacking pre-explosion observations of the host galaxy of
SN 2003du, we constructed template images using observations
which we obtained more than one year after SN maximum light.
The SN magnitudes were measured by PSF-fitting. The small
SN contribution was then subtracted and the images were visu-
ally inspected for over- or under-subtraction (none was noticed).
The best seeing images were then combined to form the tem-
plates. The subtraction of the host galaxy from the ”SN + host”
images was done with Alard’s (Alard & Lupton, 1998; Alard,
2000) optimal image subtraction software, slightly modified and
kindly made available to us by B. Schmidt. When using galaxy
templates built in this way, any improperly subtracted SN light
will introduce systematic errors into the subsequent photometry.
In the case of SN 2003du this should, however, be negligible be-
cause at the epochs used to build the templates, the SN was much
fainter than on the images to which the template subtraction was
applied (at least 2 mag fainter at +220 days and 4–5 mag fainter
over the first three months after maximum). Even if we conser-
vatively assume that the final templates still contained 20% of
4 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
the SN light, the error introduced would be at most 0.03 mag
at +220 days and clearly negligible during the first 3-4 months
after maximum.
The SN magnitudes were measured differentially with re-
spect to the field stars indicated with numbers in Fig. 1. The
instrumental magnitudes were measured by aperture photometry
for observations before September 2003 and by PSF fitting at the
later epochs. The magnitudes of the field stars were calibrated
for two photometric nights at the Nordic Optical Telescope –
May 15 and 16, 2003. On each night, the field of the globular
cluster M92 that includes the standard stars listed in Majewski
et al. (1994) was observed at four airmasses between 1.06 and
1.8. The BVRI magnitudes of the standard stars were taken from
(Stetson, 2000)2, while the U magnitudes were calculated from
the U − B values given in Majewski et al. (1994). The standard
star magnitudes were measured with PSF photometry and aper-
ture corrections were applied to convert the PSF magnitudes to
magnitudes in an aperture with a radius of five times the see-
ing. Following Harris et al. (1981), all measured magnitudes
were fitted simultaneously (with 3σ clipping) to derive linear
transformation equations, with the additional requirement that
the color-terms and the zero-points to be the same for the two
nights. Second-order extinction terms were not included. The
calibrations for the two nights agree very well within the es-
timated photometric (statistical) errors. The weighted average
magnitudes from the calibration in the two nights and the corre-
sponding errors are given in Table 2. Note that the uncertainties
of the calibrated magnitudes are donated by the uncertainty of
the zero-point and not by the statistical uncertainty. A compari-
son between the stars in common with Leonard et al. (2005) and
Anupama et al. (2005) reveals that there are small systematic dif-
ferences between the photometry; ours being generally brighter.
The mean differences with the BVRI photometry of Leonard
et al. (2005) are, respectively, 0.010 ± 0.020, 0.013 ± 0.020,
0.039 ± 0.010 and 0.013 ± 0.027 mag. Excluding star #1 which
is brighter in Anupama et al. (2005) in all bands, the mean dif-
ferences are 0.00±0.05, 0.06±0.01, 0.04±0.01, 0.06±0.02 and
0.015 ± 0.010 mag for the UBVRI bands, respectively. Some of
these differences are non-negligible and we have no explanation
of why they appear in the comparison stars calibrations. This
is clearly worrisome and emphasizes one important source of
systematic errors when different SN data sets are combined and
used to derive cosmological parameters.
Landolt (1992) standard fields were observed to derive the
instrument color-terms (ct), allowing us to transform the pho-
tometry of SN 2003du to the standard Johnson-Cousins system.
The instrumental magnitudes of the standard stars were mea-
sured by aperture photometry with large apertures. All measure-
ments for a given instrument were fitted simultaneously (with
3σ clipping) with linear equations of the form:
U − u = ctU(U − B) + zp , B − b = ctB(B − V) + zp
V − v = ctV (B − V) + zp , R − r = ctR(V − R) + zp (1)
I − i = ctI(V − I) + zp
to determine the cts. The upper-case and lower-case letters de-
note the standard and instrumental magnitudes, respectively.
For each SN image, a zero-point was calculated for each
calibrated star by applying Eqs. 1. The final image ZP and its
uncertainty are, respectively, the average of the individual ZPs
2 Available at http://cadcwww.hia.nrc.ca/standards/ and as
discussed by Stetson (2000) this photometry is essentially in the Landolt
(1992) system.
(with 3σ outliers removed if present) and the standard deviation.
The measured scatter for the brightest stars was always larger
than expected from Poisson statistics. This indicates that there
are additional sources of uncertainties: imperfect flat-fielding,
presence of non-uniform scattered light, CCD non-linearity, etc.
Considering the magnitude scatter of the brightest stars we esti-
mate that these effects contribute ≤ 0.01 mag to the error budget.
Finally, the ZPs were added to the measured SN magnitudes to
obtain the magnitudes in the natural systems of the instruments
used, mnat.
The SN magnitudes can be transformed to a standard photo-
metric system using the color corrections obtained with Eqs. 1.
It is, however, well known that these color corrections do not
work well for SNe and significant systematic differences be-
tween photometry obtained with different instruments are of-
ten observed (Suntzeff, 2000; Stritzinger et al., 2002; Krisciunas
et al., 2003). The reason is that the SN spectral energy distribu-
tion (SED) is very different from that of normal stars. Another
consequence of this is that if a given band is calibrated against
different color indices, e.g. V(B − V) and V(V − R), one would
get the same magnitude for normal stars but slightly different
magnitudes for objects with non-stellar SEDs. This is because
the color-terms are determined with normal stars, but SNe oc-
cupy a different region in the color-color diagrams. The pho-
tometric observations of SN 2003du were collected with many
different instruments and we chose to standardize the photome-
try using the S-correction method described by Stritzinger et al.
(2002) coupled with our very well-sampled spectral sequence
of SN 2003du. The S-correction method assumes that the SED
of the SN and the response of the instruments used for the ob-
servations are both accurately known. Then one can correct the
photometry to any well-defined photometric system by means
of synthetic photometry. If f phot
(λ) is the photon flux of the ob-
ject per unit wavelength, mnat the object magnitude as defined
above, Rnat(λ) the response of the natural system and Rstd(λ) the
response of the standard system, then the object standard mag-
nitude mstd is:
mstd = mnat −2.5 log
(λ)Rstd(λ)dλ
+2.5 log
(λ)Rnat(λ)dλ
+const (2)
The constant in Eq. 2 is such that the correction is zero for A0 V
stars with all color indices zero. This ensures that for normal
stars the synthetic S-correction gives the same results as the lin-
ear color-term corrections (Eq. 1). The constant can be deter-
mined from synthetic photometry of stars for which both pho-
tometry and spectrophotometry is available. The details of the
application of the S-corrections are given in the Appendix. In
Fig. 2 we only show the time evolution of the difference between
the S-correction and the linear color-term correction. Note the
particularly large difference for Calar Alto I, and NOT R and
I-bands, as well as the rather large scatter for the V-band at all
epochs and for the B-band after +20 days.
The final photometry of SN 2003du is given in Table 3. Note
that none of the U-band and part of the BVRI photometry could
be S-corrected. Additional B and V photometry obtained at
Moscow and Crimean Observatories is given in Table 4. Figure 3
shows a comparison between the S-corrected and color-term cor-
rected B − V color index and I magnitudes. It is evident that
in the color-term corrected photometry small systematic differ-
ences between the various setups exist. It is also evident that
the S-correction removes those differences to a large extent, the
exception being the BAO data at early epochs. Significant im-
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 5
−0.06
−0.04
−0.02
B−band
Days from Bmax
Asiago
Calar Alto
−0.06
−0.04
−0.02
0.04 V−band
0 50 100
−0.04
−0.02
R−band
0 50 100
I−band
Fig. 2. Time evolution of the difference be-
tween the S-correction and the linear color-
term correction.
provement is also achieved for the I-band, which required the
largest S-corrections.
2.3. Near infrared photometry and spectroscopy
Near infrared JHK photometry of SN 2003du was obtained on
six nights at TNG and NOT. The two telescopes use identical J
and H filters, but the TNG uses a K′ while the NOT has a Ks
filter (Tokunaga et al., 2002). The observations were reduced in
the standard way, using the XDIMSUM package in IRAF.
The two nights at the NOT were photometric and standard
stars from the list of Hunt et al. (1998) were observed in or-
der to calibrate a local sequence of stars. However, only star
#3 (Fig. 1) could be reliably calibrated because it is the only
one that is faint enough to be in the linear range of the de-
tector and is bright enough to give an adequate S/N. The av-
erage NIR magnitudes of star #3 are J = 14.67, H = 14.38
and K = 14.37, all with uncertainties of ∼ 0.03 mag. The cali-
brated magnitudes are in good agreement with the 2MASS val-
ues, which are J = 14.633 ± 0.037, H = 14.362 ± 0.056 and
K = 14.311 ±0.062. Star #3 was used to calibrate the TNG pho-
tometry. No color terms were applied. The NIR photometry of
SN 2003du is given in Table 5.
Eleven low-resolution NIR spectra of SN 2003du were ob-
tained at UKIRT and TNG (Table 6). At UKIRT, the spectral
range was covered by using different instrument settings. At
TNG an AMICI prism was used as disperser. In this mode the
whole NIR spectral range is provided in one exposure at the ex-
pense of having very low resolving power (≤ 100). Both sets of
observations were performed in ABBA sequences, where A and
B denote two different positions along the slit. After bias/dark
and flat field corrections, for each pair of AB images, the B im-
age was subtracted from the A image. The negative spectrum
was shifted to the position of the positive one and subtracted
from it. This resulted in an image with the sum of the spectra
but minus the sky background. All such images were summed
into a single image and the 1D spectra were then optimally ex-
tracted. We note that the optimal extraction algorithm has to be
applied on images where the pixel levels are given in the form of
actual detected counts, and so it will not work quite correctly if
applied to background-subtracted images. Special care was thus
taken to calculate the optimal extraction weights correctly. The
Table 4. Additional photometry SN 2003du.
JD Phase B V Telescope
2452765.38 −1.0 13.45 (0.01) 13.61 (0.01) 1
2452768.33 +2.0 13.49 (0.02) 13.57 (0.02) 1
2452775.38 +9.0 13.95 (0.01) 13.83 (0.01) 1
2452782.37 +16.0 14.65 (0.05) 14.17 (0.02) 2
2452786.33 +20.0 14.99 (0.06) 14.43 (0.02) 2
2452792.31 +25.9 · · · 14.73 (0.06) 3
1 – 70-cm Moscow reflector + CCD Pictor 416; 2 – 30-cm Moscow
refractor + CCD AP-7p; 3 – 38-cm Crimean reflector + CCD ST-7;
UKIRT spectra were wavelength calibrated with arc-lamp spec-
tra, while for the TNG spectra a tabulated dispersion solution
relating pixel number to wavelength was used. The dispersion of
the UKIRT spectra ranges from ∼ 5 Å pixel−1 to ∼ 25 Å pixel−1,
while for the TNG spectra, the dispersion is in the ∼ 30 Å pixel−1
– ∼ 100 Å pixel−1 range.
The A5 V star AS-24 (Hunt et al., 1998) and the F7 V star
BS5581 (from the list of UKIRT standard stars) were observed
at TNG and UKIRT respectively. The standard stars were ob-
served close in time and airmass to the SN observations. The SN
spectra were first divided by the spectra of the comparison stars
to remove the strong telluric absorption features. The result was
multiplied by a model spectrum of the appropriate spectral type,
smoothed to the instrumental resolution, to remove any residual
features due to the absorption lines of the standard, simultane-
ously providing the relative flux calibration. The UKIRT spec-
tra from the different instrument settings that did not overlap
were combined using the SN 2003du photometry and average
NIR color indices of normal SNe Ia.
3. Results
3.1. Light curves
The UBVRIJHK light curves (LCs) of SN 2003du are shown
in Fig. 4. The light curves morphology resemble that of a nor-
mal SN Ia with a well-pronounced secondary maximum in the
I-band and a shoulder in the R-band. The J-band also shows
a strong rise towards a secondary maximum. Comparison with
the photometry of Leonard et al. (2005) and Anupama et al.
6 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
−15 −10 −5 0 5 10
Asiago
Calar Alto
S−corrected
a) color−termcorrected + 0.1
40 50 60 70 80 90
S−corrected
color−term
corrected + 0.1
−10 0 10 20 30 40
Days from Bmax
   NOT    Asiago   Calar Alto
   NOT    BAO
   S−corrected
Fig. 3. Comparison between the S-corrected and color-term corrected a-
b B − V color index and c I-band magnitude. The color-term corrected
B − V data are shifted by 0.1 mag. A polynomial fit to the S-corrected
B − V data is overplotted. To highlight the differences the fit is also
plotted shifted by 0.1 mag.
Table 5. NIR photometry of SN 2003du. The observations on 10.5 and
11.5 days are from NOT. The other four are from TNG.
JD Phase J H K
[day]
2452755.41 −11.5 14.96 (0.04) 15.02 (0.04) 15.02 (0.04)
2452768.68 +1.7 14.42 (0.04) 14.66 (0.04) 14.38 (0.04)
2452773.43 +6.5 14.92 (0.04) 14.77 (0.04) 14.53 (0.04)
2452777.46 +10.5 15.67 (0.04) 14.86 (0.04) 14.70 (0.04)
2452778.51 +11.5 15.84 (0.04) 14.86 (0.04) 14.75 (0.04)
2452782.58 +15.6 16.12 (0.04) 14.85 (0.04) 14.65 (0.04)
(2005) reveals fairly good consistency. However, systematic dif-
ferences between the data sets do exist and our photometry is
generally brighter. This is probably due to the differences in the
comparison star calibrations, as well as to the fact that our pho-
tometry was S-corrected, unlike those of Leonard et al. (2005)
and Anupama et al. (2005). To estimate the differences we fit-
ted a smoothing spline function to our data and computed the
mean difference and its standard deviation from Leonard et al.
(2005) and Anupama et al. (2005) photometry. The difference
slightly varies with the SN phase. Up to 30 days after maximum
light the mean differences and standard deviations in BVRI are,
respectively, 0.068 ± 0.030, 0.046 ± 0.029, 0.047 ± 0.022 and
Table 6. Log of the NIR spectroscopy
Date (UT) JD Phase Coverage Telescopea
[day] [µm]
2003 Apr 25 2452754.89 −11.5 0.8-2.5 UK-1
2003 Apr 25 2452755.47 −10.9 0.75-2.45 TNG
2003 May 01 2452760.89 −5.5 0.8-2.5 UK-1
2003 May 04 2452763.88 −2.5 1.42-2.4 UK-2
2003 May 08 2452768.68 +2.3 0.9-2.3 TNG
2003 May 10 2452769.79 +3.4 1.39-2.50 UK-2
2003 May 11 2452770.90 +4.5 0.8-2.5 UK-1
2003 May 19 2452778.80 +12.4 1.48-2.30 UK-2
2003 May 22 2452782.58 +16.2 0.9-2.48 TNG
2003 May 27 2452786.77 +20.4 0.8-2.5 UK-1,2
2003 Jun 06 2452796.80 +30.4 0.8-2.5 UK-1,2
aTNG = TNG + NICS, UK-1/2 = UKIRT + CGS4/UIST
0.042±0.037 mag with Anupama et al. (2005) and 0.026±0.025,
0.026±0.015, 0.014±0.015 and 0.071±0.030 mag with Leonard
et al. (2005). The difference with the Anupama et al. (2005) U-
band photometry is 0.007 ± 0.085 mag.
We fitted the B-band template of Nugent et al. (2002) to the
data to determine the B-band light curve parameters. This pro-
vided the time of B maximum light tBmax (JD)=2452766.38 (2003
May 6.88 UT), stretch factor sB = 0.988±0.003 and peak magni-
tude Bmax = 13.49 ± 0.02 mag. The peak VRI magnitudes were
estimated by fitting low-order polynomials to the data around
maximum, giving Vmax = 13.57± 0.02, Rmax = 13.57± 0.02 and
Imax = 13.83 ± 0.02 mag. The U-band maximum was estimated
by fitting our own template derived from the SNe published by
Jha et al. (2006a): Umax = 13.00 ± 0.05 mag. The optical pho-
tometric coverage around 15 days after Bmax is rather sparse.
However, the B-band template matches the observed photome-
try very well, thus we are able to use this to determine the decline
rate parameter. We find ∆m15 = 1.02±0.05. BVRI template light
curves with ∆m15 = 1.02 were also generated using the data and
the method described by Prieto et al. (2006). These light curves
are also shown in Fig. 4, shifted to match SN 2003du peak mag-
nitudes. The resemblance between SN 2003du light curves and
the templates is excellent.
The NIR templates from Krisciunas et al. (2004b) were fitted
to the first three JHK photometric points (Fig. 4) to estimate the
peak magnitudes: Jmax = 14.21, Hmax = 14.56 and Kmax = 14.29
mag. The rms around the fits are fairly small 0.03, 0.02 and 0.04
mag, respectively, but because the LCs are undersampled the un-
certainties in the peak magnitudes should exceed these values.
To derive the templates, Krisciunas et al. (2004b) fitted third-
order polynomials to the photometry of a number of SNe. The
rms around the fits are 0.062, 0.080 and 0.075 mag for J, H and
K, respectively. These numbers were added in quadrature to the
rms around the fits to the SN 2003du data to obtain the uncer-
tainties of the JHK peak magnitudes, 0.07, 0.08 and 0.09 mag,
respectively.
The entire light curves are shown in the inset of Fig. 4. The
late-time HS T data from Leonard et al. (2005) are also shown
(open symbols); these are consistent with our ground based pho-
tometry. After ∼ +180 days the magnitudes of SN 2003du de-
cline linearly, following the expected form of an exponential ra-
dioactive decay chain. The decline rates in magnitudes per 100
days in UBVRI-bands (as determined by linear least-squares fit-
ting) are 1.62 ± 0.12, 1.47 ± 0.02, 1.46 ± 0.02, 1.70 ± 0.06 and
1.00 ±0.03, respectively. The decline rates in the B- and V-bands
are virtually the same. The I-band decline on the other hand is
much slower than in the other bands. Many other normal SNe Ia
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 7
0 50 100 150
Days from Bmax
0 50 100 150 200 250 300 350 400 450 500
Days after Bmax
Fig. 4. UBVRIJHK light curves of SN 2003du. The error bars are not plotted because they are typically smaller than the plot symbols. For the
BVRI bands the filled and the open symbols are the S-corrected and non-S-corrected photometry, respectively. The open symbols for J band are
synthetic photometry from the combined optical-NIR spectra. Overplotted are the B-band template of Nugent et al. (2002), the JHK templates
from Krisciunas et al. (2004b) (solid lines), as well as our U-band template derived from Jha et al. (2006a) data (dashed line). The dotted lines are
a light curve template with ∆m15 = 1.02 calculated as described in Prieto et al. (2006) using a program provided by the authors. Inset: The full
light curves. The late-time HS T data from Leonard et al. (2005) are also shown with the open symbols. The linear fits to the late-time photometry
are also shown.
(e.g., Lair et al., 2006) and the peculiar SN 2000cx (Sollerman
et al., 2004) also show similar behavior.
3.2. Reddening in the host galaxy
Figure 5 shows that the time evolution of the color indices (CIs)
of SN 2003du closely follows the reddening corrected CIs of
normal SNe such as 1990N, 1998aq, and 1998bu, as well as the
Nobili et al. (2003) templates. This implies that SN 2003du was
probably not reddened within its host galaxy. Nevertheless, the
reddening in the host galaxy was estimated with three different
methods. The CIs of SN 2003du were first corrected for the small
Milky Way reddening of E(B−V) = 0.01 (Schlegel et al., 1998)
assuming RV = 3.1.
i) Phillips et al. (1999) use the observed Bmax − Vmax and
Vmax−Imax indices, and the evolution of B−V between 30 and 90
days after maximum to derive E(B− V). The first two quantities
are weak functions of ∆m15. The time evolution of B−V (known
as the Lira relation) seems to hold for the majority of SNe Ia
(Phillips et al., 1999; Jha et al., 2006b). Following Phillips et al.
(1999), for SN 2003du we obtain E(B − V)max = −0.01 ± 0.04,
E(V − I)max = 0.07 ± 0.05 and E(B − V)tail = 0.05 ± 0.07.
8 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
Lira−Phillips relation
2003du
1990N
1998bu
1998aq
Nobili et al. (2003)
−20 0 20 40 60 80 100
Days from Bmax
−20 0 20 40 60 80 100
Days from Bmax
Fig. 5. The evolution of the optical color indices of SN 2003du, compared with those of other well-observed SNe Ia. When necessary the colors
were de-reddened with the appropriate E(B − V). The Nobili et al. (2003) B − V , V − R and V − I templates are also shown.
The errors indicate the intrinsic accuracy of the three methods as
given in Phillips et al. (1999), viz. 0.03, 0.04 and 0.05, added in
quadrature to the uncertainties of the observed CIs. Note that the
B − V evolution of SN 2003du has a different slope from that of
the Lira relation, leading to rather a large scatter of ∼ 0.07 mag.
We averaged the above estimates of E(B − V)max, 0.8×E(V −
I)max
3 and E(B−V)tail weighted by their respective uncertainties
to obtain the final reddening estimate: E(B−V) = 0.027 ±0.026.
ii) Wang et al. (2003b) introduced a novel method,
CMAGIC, to estimate the brightness and the reddening of
SNe Ia. It is based on the observation that between 5-10 to 30-
35 days after maximum the B magnitude is a linear function of
B − V with a fairly uniform slope. Applying this method, we
obtain E(B − V) = 0.00 ± 0.05.
iii) Krisciunas et al. (2000, 2001, 2004b) have shown that
the intrinsic V − (JHK) CIs of SNe Ia are very uniform and can
be used to estimate the reddening of the host galaxy. Figure 6
shows the V − (JHK) CIs of SN 2003du overplotted with the
unreddened loci for mid- (∆m15 = 1.0 − 1.3) and slow-declining
SNe (∆m15 = 0.8− 1.0) of Krisciunas et al. (2004b). Most of the
V − (HK) data of SN 2003du fall between the two loci. This is
consistent with the fact that its ∆m15 = 1.02 lies between these
two groups of SNe Ia. Although the V − J CI is slightly redder
than the locus, overall the V − (JHK) CIs of SN 2003du suggest
little reddening.
Combining the results of the three estimates we conclude
that SN 2003du suffered negligible reddening within the host
galaxy. The main parameters of SN 2003du that we derived from
photometry are summarized in Table 7.
3 the factor 0.8 serves to convert E(V − I) to E(B − V) assuming the
standard Milky Way extinction law with RV = 3.1.
slow-decliners (∆m15=0.8-1.0)
mid-decliners  (∆m15=1.0-1.3)
-10 0 10 20 30
Days from Bmax
Fig. 6. V − (JHK) color indices of SN 2003du. The unreddened loci
for mid- and slow-declining SNe of Krisciunas et al. (2004b) are over-
plotted. The open symbols are estimates based on synthetic photometry
from the combined optical-NIR spectra.
3.3. Spectroscopy
Our collection of optical spectra of SN 2003du is shown in
Figs. 7 and 8. The spectra marked with an asterisk have been
smoothed using the á trous wavelet transform (Holschneider
et al., 1989). The optical spectral evolution of SN 2003du is
that of a normal SN Ia. In the earliest spectrum at −13 days the
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 9
4000 6000 8000 10000
Rest frame wavelength [Å]
−12.8 *
−10.9
−10.8
−7.8 *
+10.0
+15.1
+17.2
+18.2
+19.0
+21.1
+26.1
+31.2 +34.1
+39.0
+45.2
+51.1
+63.1
+72.0
+84.0
+108.9
+141.4
high−velocity Ca II
HV Ca II
Fig. 7. Evolution of the optical spectra of SN 2003du. The spectra marked with an asterisk were slightly smoothed (see text for details). The
noticeable telluric features are marked with Earth symbols; the connected symbols mark the region of strong telluric absorption.
Si ii λ6355 line is strong and broad (∼ 10000 km s−1 full-width
at half-depth), and the S ii λ5454 and λ5640 lines are well devel-
oped. In the −11 day spectrum the Ca ii H&K and the IR triplet
lines are also very strong. In all the spectra until one week after
maximum light, Si ii λ4129 and λ5972 lines are clearly visible.
Mg ii λ4481, Si iii λλ4553,4568 and the blend of Fe ii, Si ii and
S ii lines around 4500–5000 Å are also prominent. A few days
after Bmax the spectrum starts to be dominated by Fe group ele-
ments and gradually evolves into a nebular spectrum.
The ratio between the depth of the Si ii λ5972 and λ6355
lines, R(Si ii) (Nugent et al., 1995), at maximum is R(Si ii) =
0.22 ± 0.02, typical for normal SN Ia. R(Si ii) does not change
significantly in the pre-maximum spectra, remaining at ∼ 0.2.
In Fig. 9 three of the pre-maximum spectra of SN 2003du are
compared with spectra of other normal SNe Ia observed at sim-
ilar epochs and appropriately de-reddened. For this and other
comparison plots we use published optical spectra of SN 1994D
(Patat et al., 1996; Filippenko, 1997; Meikle et al., 1996),
SN 1990N (Leibundgut et al., 1991), SN 1996X (Salvo et al.,
2001), SN 1999ee (Hamuy et al., 2002), SN 1998aq (Branch
et al., 2003), SN 1998bu (Jha et al., 1999; Hernandez et al.,
2000), SN 2002er (Kotak et al., 2005), SN 2001el (Wang et al.,
10 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
Table 7. Main photometric parameters of SN 2003du from this work.
tBmax [JD] 2452766.38 ± 0.50
tBmax (UT date) May 6.88, 2003
B-band stretch, sB 0.988±0.003
B-band decline rate, ∆m15 1.02±0.05
Peak magnitudes U = 13.00 ± 0.05 B = 13.49 ± 0.02
V = 13.57 ± 0.02 R = 13.57 ± 0.02
I = 13.83 ± 0.02 J = 14.21 ± 0.07
H = 14.56 ± 0.08 K = 14.29 ± 0.09
Late-time decline γU = 1.62 ± 0.12 γB = 1.47 ± 0.02
rate γ [mag/100 days] γV = 1.46 ± 0.02 γR = 1.70 ± 0.06
γI = 1.00 ± 0.03 γBol = 1.40 ± 0.01
E(B − V)host 0.00±0.05
4000 5000 6000 7000 8000
Rest frame wavelength [Å]
+195.9 *
+195.9
+209.3 *
+221.3
+272.3 *
+376.9
SN 1998bu
Fig. 8. Nebular spectra of SN 2003du. The spectra marked with an aster-
isk were slightly smoothed. A nebular spectrum of SN 1998bu is shown
for comparison.
2003a; Mattila et al., 2005) and SN 2005cg (Quimby et al.,
2006). The spectra at about 10 days before maximum show sig-
nificant differences. The spectra have not been taken at exactly
the same phase and the rapid spectral evolution at such early
phases may partly be responsible for the differences. However,
most of the differences are most likely intrinsic. It worths noting
that the weak feature at ∼6300 Å that is visible in the two earliest
spectra of SN 2003du is present in other SNe Ia as well (Fig. 10)
and has been attributed to C ii λ5860 (Mazzali, 2001; Branch
et al., 2003; Garavini et al., 2004, 2005). At one week before
maximum the spectra are more similar to each other. It is inter-
esting to note that at these epochs the largest differences between
the SNe are seen in the strengths and profiles of the Si ii λ6355,
Ca ii H&K and Ca ii IR3 lines. Starting from one week before
maximum the spectra of most SNe Ia are very homogeneous.
The NIR spectra of SN 2003du are shown in Fig. 11. The
earliest spectra at −11.5 and −11 days are rather featureless with
only hints at weak broad P-Cygni profiles. The weak ∼ 1.05µm
absorption could be due to Mg ii λ10926 or He i λ10830 (or a
combination of the two) (Meikle et al., 1996; Mazzali & Lucy,
1998; Branch et al., 2004; Marion et al., 2003). The strength
of this absorption in the earliest two spectra is quite different,
despite the fact that they have been taken only half a day apart.
In the −11.5 days spectrum, however, the absorption is likely
99ee −9d
90N  −14d
03du −12.8d
03du −10.9d
01el −9d
98aq −9d
02er −11d
94D −12d
Early spectra (day −11)
Ca II H&K
Ca II IR3
Si II
4000 6000 8000 10000
Rest frame wavelength [Å]
99ee −7d
90N  −7d
03du −5.8d
98bu −6.5d
98aq −8d
02er −6.3d
94D −7.5d
one week before maximum
Fig. 9. Comparison of optical spectra of normal SNe Ia at two pre-
maximum epochs. The arrows in the lower panel mark the lines whose
velocities have been measured.
enhanced by a noise spike due to the low instrument response at
this wavelength.
In the day −5.5 spectrum an absorption due to Mg ii λ9226
(Marion et al., 2003) is clearly seen. In the earlier IR spec-
tra there are only hints of its presence and it may be just de-
tectable in the optical spectrum at day −11. Our experiments
with the SN spectral synthesis code SYNOW (see for details,
e.g. Branch et al., 2003) show however, that Si iii and possibly
Si ii may contribute to the red part of this line. No other fea-
tures are detected in the 0.9-1.2µm spectral region. In particular,
no C i or O i lines are observed, in accordance with the findings
of Marion et al. (2006). The absorption at ∼ 1.21µm is due to
Ca ii according to Wheeler et al. (1998), but the associated emis-
sion peak at ∼ 1.24 µm was attributed to Fe iii by Rudy et al.
(2002) in SN 2000cx. The 1.6µm absorption seen in the spectra
until maximum light is due to Si ii with a possible contribution
from Mg ii (Wheeler et al., 1998; Marion et al., 2003). The broad
features beyond ∼ 1.7µm lack clear identification. Possible con-
tributors are Si iii at ∼ 2 µm (Wheeler et al., 1998) and Co ii at
∼ 2 − 2.05µm and ∼ 2.3 µm (Marion et al., 2003).
By day +12, two strong emission features at ∼ 1.55µm and
∼ 1.75µm dominate the 1.4-1.8µm spectral region. These two
features are formed by blending of many Fe ii, Co ii and Ni ii
emission lines (Wheeler et al., 1998). Lines of Fe ii, Co ii, Ni ii
and Si ii dominate the spectral region beyond 2 µm. From day
+15, a number of lines, with uncertain identifications also de-
velop in the J band. One can also clearly see how a flux deficit
at ∼ 1.35µm develops. This causes the very deep minimum ob-
served in the J-band light curves of most SNe Ia around 20 days
after maximum.
Figure 12 presents a comparison of several IR spectra of
SN 2003du with those of other normal SNe: SN 1994D (Meikle
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 11
5600 6000 6400
Rest frame wavelength [Å]
03du −12.8
03du −10.9
99ac −15
98aq −9
96X −4
94D −10
90N −14
C II 6580?
Fig. 10. Early spectra of SN 2003du and several other SNe Ia zoomed at
the Si ii 6355 line. The dotted lines mark the weak absorption features
that may be due to C ii λ6580.
et al., 1996), SN 1999ee (Hamuy et al., 2002), SN 1998bu (Jha
et al., 1999; Hernandez et al., 2000; Hamuy et al., 2002), and
SN 2002bo (Benetti et al., 2004). Similarly to the optical, the IR
spectra of normal SNe taken at similar epochs are very homoge-
neous, even the spectra taken 6–12 days before maximum. The
only significant difference is in the J-band, where the Mg ii lines
of SN 2002bo are stronger compared to other SNe.
3.4. Blueshifts of absorption-line minima
We have measured the blueshifts of the absorption-line min-
ima of Si ii λ6355, S ii λ5640 and Si iii λλ4553,4568, which are
thought to be relatively un-blended (Branch et al., 2003), by fit-
ting a Gaussian to the line absorption troughs. In the rest of
the paper we report the velocities that correspond to the mea-
sured blueshifts of the absorption-line minima (unless otherwise
stated) and will refer to these as velocities of the absorption lines.
By convention, these velocities are negative and we say that the
velocity of a line increases from, e.g. −20000 to −10000 km s−1.
The velocities inferred from an explosion model will be reported
as positive numbers.
The velocities of the Si ii λ6355, S ii λ5640 and
Si iii λλ4553,4568 lines are shown in Fig. 13 and it is evi-
dent that the time evolution is very similar to that in other
normal SNe Ia (see, e.g. Benetti et al., 2005). The Si ii λ6355
velocity initially increases rapidly, but 7–5 days before max-
imum the increase rate slows down and the velocity remains
almost constant thereafter. The velocities of the S ii λ5640
and Si iii λλ4553,4568 lines increase at nearly constant rate;
however, there is a hint that the S ii λ5640 velocity remains
constant after maximum, similarly to Si ii λ6355. Benetti et al.
(2005) measured a post-maximum velocity increase rate of
the Si ii λ6355 line to be v̇ = 31 ± 5 km s−1d−1 and classified
SN 2003du as a Low Velocity Gradient SN Ia, along with
other normal and all overluminous SNe Ia. It can be seen
from Fig. 1 in (Benetti et al., 2005) that before maximum the
Si ii λ6355 velocities of SN 2003du are systematically higher by
500-2000 km s−1 compared to all other SNe.
During the SN photospheric epochs the main source of
continuum opacity at the optical wavelengths is electron scat-
tering and following Jeffery et al. (1992) we adopt that the
1.0 1.5 2.0 2.5
Rest frame wavelength [µm]
 −11.5
 −10.9
  −5.5
  −2.5*
  +2.3
  +3.4*
  +4.5
 +12.4*
 +16.2
 +20.4
 +30.4
Mg II + He I?
Mg II
Si II/Mg II?
Ca II
Ca II
Fe III?
Si III?
Co II?
Co II?
Ca II
Fe/Si edge
Fe/Ni/Co
Fe II
Fe/Ni/Co/Si
Fe/Ni/Co/Si?
Fig. 11. NIR spectral evolution of SN 2003du. The spectra marked with
an asterisk have been smoothed (only the J band of the −2.5 days spec-
trum is smoothed).
(continuum) photosphere is at electron scattering optical depth
2/3. However, the velocity gradient in the expanding SN ejecta
causes many weak lines to overlap which gives rise to strong
pseudo-continuum (e.g., Pauldrach et al., 1996), and the so-
called expansion opacity (Karp et al., 1977; Pinto & Eastman,
2000) is an analytical description of this effect. This expan-
sion opacity may exceed electron scattering opacity by orders
of magnitude. The velocity of the pseudo-photosphere thus cre-
ated is wavelength-dependent. Besides, strong absorption lines
may form in a large volume above the continuum photosphere.
For these reasons, the line velocities we measure most likely do
not trace the velocity of the continuum photosphere and should
be interpreted with caution. Lentz et al. (2000) have computed
a grid of photospheric phase atmospheres of SNe Ia with differ-
ent metallicities in the C+O layer and computed non-LTE syn-
thetic spectra. It would be more reasonable for us to compare the
Si ii λ6355 line velocities in SN 2003du with the measurements
from the Lentz et al. (2000) synthetic spectra. The time evolution
is qualitatively similar and in Fig. 13 we also show the measure-
ments for the 1/3 Solar metallicity models, which best follows
the SN 2003du Si ii λ6355 line blueshift.
12 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
1.0 1.5 2.0 2.5
Rest frame wavelength [µm]
03du −11.5
99ee −9
02bo −9.2
94D −8.5
03du −5.5
03du −2.5
98bu −3
03du +2.3
99ee +2
03du +4.5
99ee +5
03du +16.2
98bu +15
Fig. 12. Comparison with NIR spectra of other normal SNe Ia.
Marion et al. (2003) showed that the velocities of lines in
NIR spectra could be used to constrain the location of the tran-
sition region between the layers of explosive carbon and oxygen
burning, and incomplete to complete silicon burning, and hence
place constraints on the explosion models. We measured the ve-
locities of the blue edges of the absorptions at ∼ 0.9 µm and
1.05µm in our optical and IR spectra between −11.5 and +4.5
days. Both lines show constant velocities of ∼ −11000 km s−1
and ∼ −13000 km s−1, respectively, assuming that the lines are
formed by Mg ii λ9226 and Mg ii λ10926. The constant veloc-
ity indicates that the continuum photosphere is well beneath the
Mg-rich layers (Meikle et al., 1996). The velocity of the sharp
edge at ∼ 1.55 µm in the spectra between +10 and +20 days
can be used to estimate the transition between the layers of
incomplete and complete silicon burning. We measure veloci-
ties ≤ −9800 km s−1 which is similar to the results of Marion
et al. (2003) and is also broadly consistent with their refer-
ence explosion model in which Si is completely consumed be-
low ∼ 8500 km s−1. This ties in with the measurements of the
Si ii λ6355 line velocity, which is always ≤ −9300 km s−1.
4. Discussion
4.1. The distance to SN 2003du
We have shown that SN 2003du was a spectroscopically and
photometrically normal SN Ia, and furthermore that it was not
reddened within its host galaxy. The distance to UGC 9391 has
not been measured using direct techniques, and the only avail-
−10 0 10 20 30 40
Days from Bmax
− Si II λ6355
− Si III λ4560
− S II λ5640
Lentz model
1/3 Solar metallicity
Fig. 13. The evolution of the velocity of the absorption lines of
SN 2003du.
able information is from its recession velocity. The observed
velocity is 1914 km s−1, which after correcting for the Local
Group in-fall onto Virgo becomes 2195 km s−1 (from the LEDA
database) or a distance modulus of µ = 32.42 mag on the scale
of H0 = 72 km s
−1,Mpc−1.
Recently, Riess et al. (2005) calibrated the luminosities of
SN 1998aq and SN 1994ae by observing Cepheids in their host
galaxies with the Hubble Space Telescope. Including two other
SNe Ia with Cepheid calibrated distances, they estimated the
absolute magnitude of a typical SN Ia to be MV = −19.20
±0.10(statistical)±0.115(systematic) mag. Meikle (2000) and
Krisciunas et al. (2004a,c) presented evidence that SNe Ia are
standard candles in the NIR and that no correction for the light
curve shape is needed for SNe with ∆m15 < 1.7 mag. Krisciunas
et al. (2004c) derived the following absolute peak JHK mag-
nitudes for H0 = 72 km s
−1,Mpc−1: −18.61,−18.28 and −18.44
mag all with statistical uncertainty of ∼ 0.03 mag. The system-
atic uncertainty of MV is mostly due to the 0.1 mag uncertainty in
the distance to the Large Magellanic Cloud (LMC) and hence it
also affects the NIR absolute magnitudes and the distance mod-
ulus derived from the host galaxy recession velocity (through
H0). The light curve decline rate parameter ∆m15 = 1.02 ± 0.05
and the normal spectral evolution suggest that SN 2003du is very
similar to normal SNe Ia. If one assumes that SN 2003du had the
above-mentioned absolute VJHK magnitudes, a distance mod-
ulus of µ = 32.79 ± 0.04 (or a radial velocity of ∼ 2600 km s−1
with H0 = 72 km s
−1,Mpc−1) is obtained 5. This estimate is the
average of the four individual estimates weighted by their sta-
tistical uncertainties, i.e. the errors of SN 2003du peak VJHK
magnitudes added in quadrature to the statistical uncertainties of
the absolute magnitudes.
The difference between the two distance moduli is 0.37 mag
(it will further increase if the Meikle 2000 absolute NIR mag-
nitudes are used) and indicates that SN 2003du was fainter than
the average of SNe with ∆m15 = 1.02. The 1σ dispersion of
SNe Ia absolute magnitudes in both, optical and IR, is ∼ 0.15
mag (e.g., Phillips et al., 1999; Krisciunas et al., 2004c). The
4 Riess et al. (2005) estimated H0 = 73 km s
−1,Mpc−1 and
MV = −19.17, and we converted their MV to the scale of H0 =
72 km s−1,Mpc−1
5 The absolute JHK magnitudes of Meikle (2000) are by 0.4 mag
brighter than those of Krisciunas et al. (2004c). The distance moduli
derived with the values from the latter paper are consistent with the
estimates of absolute V magnitude from Riess et al. (2005); we therefore
adopt the Krisciunas et al. (2004c) values.
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 13
uniformity and the small dispersion of the V − [JHK] colors
of SNe Ia (Krisciunas et al., 2004b) indicates that the intrinsic
scatter in the VJHK bands is correlated, and so cannot be re-
duced by averaging observations in different bands. Therefore,
the distance modulus we estimate, µ = 32.79 ± 0.04 mag, has
an additional ∼ 0.15 mag uncertainty from the intrinsic disper-
sion of SNe Ia luminosity. The fact that SN 2003du is 0.37 mag
fainter than expected for SNe with ∆m15 ∼ 1.02 may thus be
due to the intrinsic scatter (2.5σ from of the mean). It is also
possible that UGC 9391 may not be in the undisturbed Hubble
flow: if it has vr = 2600 km s
−1 and a peculiar velocity compo-
nent of ∼ 400 km s−1 toward the Earth, it may seem closer than
it really is. UGC 9391 is nearly face-on and the contribution of
the galaxy rotation should be small.
4.2. The bolometric light curve
In order to compute the uvoir ”bolometric” light curve (i.e. the
flux within the 0.2-2.4µm interval) of SN 2003du we proceeded
as follows. First, our U-band template LC was fitted to the U
photometry in order to estimate the U magnitudes when only
BVRI were available. The magnitudes were corrected for the
small Galactic reddening and transformed to flux densities us-
ing the absolute calibration of the UBVRI system by Bessell
et al. (1998). A cubic spline was fitted through the data points
and the resulting fit was integrated numerically over the interval
3500-9000 Å.
Most of the early-time SN Ia luminosity is emitted at optical
wavelengths, however, a non-negligible correction for the flux
emitted outside the optical wavelengths is also needed (see, e.g.
Suntzeff, 1996). The flux emitted beyond 9000 Å was estimated
by integrating the combined optical-NIR spectra of SN 2003du.
The filled circles in Fig. 14a show the time evolution of the ra-
tio of the flux emitted in the 9000-24000Å range to that emit-
ted within 3500-9000 Å. Suntzeff (1996) finds that at +80 days
less than 10% of the flux is emitted in the IR. We estimate from
the photometry of SN 2001el (Krisciunas et al., 2003) that the
contribution of the IR flux is ∼ 25% and ∼ 15% at +28 and
+64 days, respectively. This is consistent with our estimates for
SN 2003du and the findings of Suntzeff (1996), and indicates
that the contribution of the IR flux decreases roughly linearly
between days +30 and +80.
As there are no UV spectra of SN 2003du observed, we used
UV spectra of other SNe Ia to estimate the contribution of the
UV flux. These comprised combined de-reddened UV-optical
spectra of SN 1990N at −14 and −7 days (Leibundgut et al.,
1991), SN 1989B at −5 (Wells et al. 1994 and UV spectra from
the IUE archive), SN 1981B (Branch et al., 1983), SN 1992A
at +5, +9 and +17 (Kirshner et al., 1993), and SN 2001el be-
tween +30 and +66 (from HS T archive). For spectra that did
not cover the full 2000–9000 Å range we extrapolated to 9000 Å
using spectra of SN 2003du. The spectra of SN 2001el were lin-
early extrapolated from ∼ 2900 Å down to 2000 Å assuming that
the flux approached zero at 1000 Å. In Fig. 14a we show the ra-
tios of the fluxes in the 2000–3500Å range to those in the 3500–
9000 Å range (open symbols).
The total contribution of the UV and IR fluxes is plotted as
a dashed line in Fig. 14a, and one can see the particularly large
corrections needed before the B-band maximum and around the
secondary I-band maximum. Beyond +80 days we assumed a
constant IR contribution of 10% and that the UV contribution
decreases linearly from 5% at +80 days to zero at +500 days.
This correction was applied to the optical fluxes to derive the
uvoir fluxes of SN 2003du. These were converted to luminos-
ity assuming a distance modulus µ = 32.79 mag. The uvoir
”bolometric” light curve of SN 2003du is shown in Fig. 14b.
For comparison, we also show the bolometric light curve of
SN 2005cf (Pastorello et al., 2007b), which is very similar to
that of SN 2003du. The maximum uvoir ”bolometric” luminos-
ity of SN 2003du is 1.35(±0.20) × 1043 erg s−1 at ∼ 2 days
before the B-band maximum. Using Arnett’s Rule as formu-
lated by Stritzinger & Leibundgut (2005, their Eq. 7)) we es-
timate the amount of 56Ni synthesized during the explosion,
M56Ni = 0.68 ±0.14 M⊙. The error is a simple propagation of the
uncertainty of the bolometric peak luminosity and the relation
of Stritzinger & Leibundgut (2005). However, Khokhlov et al.
(1993) have shown that the simplifying assumptions made in the
derivation of Arnett’s rule may lead to errors as large as 50%.
Combined with the uncertainty of the distance to SN 2003du,
clearly this estimation of the 56Ni mass is subject to large sys-
tematic uncertainty. Note, however, that Stritzinger et al. (2006)
have analyzed a nebular spectrum and the optical photometry
of SN 2003du, and derived M56Ni ≃ 0.6 M⊙, which is in good
agreement with our estimate. If one accepts a distance modulus
of µ = 32.42 mag (∼ 30.4 Mpc), then the estimated peak lumi-
nosity and M56Ni should be reduced by ∼ 30%.
4.3. Bolometric light curve modeling
To further estimate the amount of 56Ni synthesized we mod-
eled the bolometric light curve of SN 2003du for both distance
moduli µ = 32.42 and µ = 32.79 mag. We used the Monte
Carlo light curve code described by Cappellaro et al. (1997) and
Mazzali et al. (2001). Starting from an explosion model and a
given 56Ni content the code computes the transport and deposi-
tion of the γ-rays and the positrons generated by the decay chain
56Ni→56Co→56Fe in a grey atmosphere. The optical photons
that are generated by the thermalization of the energy carried by
the γ-rays and the positrons are then followed as they propagate
through the SN ejecta. The optical opacity encountered by these
photons is again assumed to be grey and to depend primarily
on the relative abundance of iron-group elements. The opacity
also decreases with time as (td/17)
−3/2, td being the time since
the explosion in days, to mimic the effect of the decreasing tem-
perature. For more details on the adopted parametrization of the
opacity see, e.g. Mazzali et al. (2001). This simple approxima-
tion works well (e.g. Mazzali et al., 2001) but an alternative view
that the opacity depends primarily on temperature has been sug-
gested (Kasen & Woosley, 2007). In Mazzali et al. (2000) the
Monte Carlo code was compared with the results from the radia-
tion hydrodynamics code of Iwamoto et al. (2000), finding very
good agreement.
We followed the approach of Mazzali & Podsiadlowski
(2006), who assumed that stable Fe-group isotopes (e.g. 54Fe,
58Ni) may be present not only in the innermost part of the ejecta
(≤ 0.2 M⊙), but also in the
56Ni zone between ∼ 0.2 M⊙ and
∼ 0.8 M⊙. Mazzali & Podsiadlowski (2006) suggested that the
scatter of SNe Ia luminosity at a given ∆m15 may be reproduced
by changing the ratio of the amount of radioactive 56Ni and the
stable isotopes in the 56Ni zone, while keeping the total mass
of the Fe-group elements constant. This ratio may be sensitive,
for example, to the metallicity of the progenitor white dwarf
(Timmes et al., 2003). The SN Ia light curve width is mainly
determined by the opacity of the ejecta, which in turn is mostly
determined by the total amount (stable and radioactive) of Fe-
group elements synthesized, provided the temperature is above
∼ 104 K (e.g. Khokhlov et al., 1993). The peak luminosity on the
14 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
−20 0 20 40 60 80
model
SN 2005cf
SN 2003du
FIR0.9−2.4µm
FUV<0.35µm
FUV+IR
−10 0 10 20
0 100 200 300 400
Days from Bmax
MC ke+=10
p.i. model
no p.i. model
SN 2003du
Co decay
Fig. 14. a: The ratio between the UV and IR fluxes to the flux within
3500-9000 Å; b: The uvoir bolometric light curves of SN 2003du, SN
2006cf and best model. The inset shows an expansion of the SN 2003du
light curve and model around maximum; c: The entire uvoir bolometric
light curve with the models overplotted.
other hand is determined by the amount of 56Ni. Therefore, if the
fraction of stable Fe-group isotopes is varied within reasonable
limits (∼ 20%) the temperature may not be affected significantly,
and thus the opacity may be effectively unchanged. This would
lead to light curves with the same width, but different luminosi-
ties.
As shown in Fig. 14b, the uvoir ”bolometric” light curve
of SN 2003du is remarkably similar to that of SN 2005cf
(Pastorello et al., 2007b) if µ = 32.79 mag is adopted. Therefore,
a model similar to that adopted for SN 2005cf can be used also
to reproduce the light curve of SN 2003du. In this case the best
fit, shown in Fig. 14b, is obtained for a model with 0.69M⊙ of
56Ni and 0.42M⊙ of stable Fe-group isotopes using the W7 ex-
plosion model (Nomoto et al., 1984) as an input. This estimate
of the amount of 56Ni is in excellent agreement with the esti-
mate derived above using Arnett’s rule. However, mixing out of
a sufficient amount of 56Ni is necessary to reproduce the early
rise of the light curve. This is a feature that is not present in
one-dimensional explosion models, but is often inferred from
SN data. For example, for SN 2002bo, using the abundance dis-
tribution and the amount of 56Ni mixed out as derived from an
abundance tomography experiment (Stehle et al., 2005) gave a
much better reproduction of the bolometric light curve. What is
interpreted as mixing in one-dimensional models may be related
to the presence of high velocity features (Mazzali et al., 2005b),
which affect the early spectra of SN 2003du quite heavily.
If the true distance modulus were µ = 32.42, the light curve
could only be reproduced if the total mass of iron group elements
was the same as above (i.e. 1.11M⊙) but the
56Ni content was
∼ 0.45 M⊙. While this may still be a possibility, with such a low
56Ni mass (less than half of the total Fe-group content) it can be
expected that the heating by radioactive decay is not sufficient to
keep the gas at a sufficiently high temperature (∼ 104K) that the
opacity is unchanged. At lower temperatures, the opacity rapidly
drops (Khokhlov et al., 1993), and thus the light curve would not
be as broad as observed. We therefore suggest that a reasonable
range of distances for SN 2003du is between µ = 32.7 and 33.0
mag, implying a 56Ni mass between 0.6 and 0.8M⊙ for a total
Fe-group elements mass of ∼ 1.1M⊙.
Roughly 200 days after maximum SN Ia ejecta become
transparent to the γ-rays and the main source of energy is the
positrons produced by the decay of 56Co. If the positrons are
fully trapped and deposit all their kinetic energy, the true bolo-
metric LC should have a decline rate of ∼ 1 mag per 100 days.
Larger decline rates are typically found in SNe Ia, and assum-
ing that the optical flux follows the true bolometric flux, this
is usually interpreted as evidence for positron escape (see, e.g.,
Colgate et al., 1980; Cappellaro et al., 1997; Ruiz-Lapuente
& Spruit, 1998; Milne et al., 1999). The uvoir ”bolometric”
luminosity decline rate of SN 2003du after 200 days is 1.4
mag per 100 days. However, late-time NIR observations of few
SNe Ia have recently been published (SN 1998bu – Spyromilio
et al. 2004; SN 2000cx – Sollerman et al. 2004; SN 2004S –
Krisciunas et al. 2007) and indicate that after 300–350 days the
NIR luminosity does not decline but stays nearly constant. The
contribution of the NIR flux therefore increases with time and if
accounted for may lead to decline rates lower than the observed
ones and closer to the full positron trapping value. Motohara
et al. (2006) obtained late-time NIR spectra (1.1-1.8µm) and H-
band photometry of SN 2003du. At +330 days SN 2003du had
an H magnitude of 20.12±0.17 (Motohara et al. private commu-
nication) and we calculate the integrated flux across the H-band
to be ∼ 3% of the optical flux at that epoch. The late-time NIR
spectra of SN 2003du indicate that the integrated J and H band
fluxes are nearly equal, implying that the contribution of the NIR
flux is at least 6%. If we adopt a 10% NIR contribution at +330
days and assume that the total NIR flux did not change after-
wards, we obtain a decline rate of 1.2 mag per 100 days, which
is still larger than the full positron trapping value.
In Fig. 14c we compare the uvoir ”bolometric” LC of
SN 2003du with the two models presented by Sollerman et al.
(2004). The models are in the form of broadband U-to-H mag-
nitudes. For a consistent comparison with SN 2003du we used
only the UBVRI model fluxes to compute the model uvoir LC in
exactly the same way as for SN 2003du. The models are generic,
and have not been tuned to any particular SN. They have been
computed with 0.6M⊙
56Ni and assume full positron trapping,
and differ only in the treatment of the photoionization repre-
senting two extreme cases that the UV photons either escape
or are fully redistributed to lower energies (for more details see
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 15
Sollerman et al. 2004 and references therein). For a comparison
with SN 2003du the models were only re-scaled to a distance
modulus µ = 32.79 mag, and yet they fit the absolute flux level
of the LC of SN 2003du quite well. It is evident from Fig. 14c
that a model with an intermediate treatment of the photoion-
ization could reproduce the SN 2003du light curve. Figure 14c
also shows a model computed with the Monte Carlo code us-
ing the best parameters we estimated above. Only the opacity
to positrons kβ+ was adjusted to fit the late-time decline rate
(Cappellaro et al., 1997). The best value is kβ+ = 10 cm
−2 g−1,
which is well within the range of values found by Cappellaro
et al. (1997).
Both late-time LC models we discussed are based on the
1D W7 explosion model and do not include a contribution from
magnetic fields. However, detailed calculations (Ruiz-Lapuente
& Spruit, 1998; Milne et al., 1999) show that the positron depo-
sition rate is quite sensitive to the magnetic field configuration
in the ejecta and the actual explosion model. Clearly, to fully ex-
ploit the information in the bolometric LC a more detailed study
is needed, but this is beyond the scope of this paper.
4.4. Evolution of Si ii λ6355, Ca ii H&K and IR triplet
Figure 15 shows the pre-maximum evolution of the absorption
lines Si ii λ6355, Ca iiH&K and Ca ii IR3 in SN 2003du (here we
also use a few spectra of SN 2003du from Gerardy et al. 2004
and Anupama et al. 2005) and other SNe Ia. In the −13 days
spectrum of SN 2003du the Si ii λ6355 line is broad and rather
symmetric. In the −11 day spectrum the line is asymmetric and
narrower, but around a week before maximum becomes sym-
metric again and the profile does not change much until max-
imum. The line evolution in SN 1994D is very similar, but is
delayed with respect to SN 2003du: the −13 and −11 day spec-
tra of SN 2003du are most similar to those of SN 1994D at −11
and −9 days. Similar evolution is also observed in SN 2001el,
SN 1990N, SN 1999ee and SN 2005cg, but the pre-maximum
coverage of these SNe is rather sparse. Nevertheless, this profile
evolution may be explained if the Si ii λ6355 line is a blend of
two components. At 10− 14 days before maximum, the strength
of the two components should be nearly equal. The blue compo-
nent then decreases very rapidly, disappearing by ∼ 7 − 5 days
before maximum, while the red component increases in strength.
In SN 2003du, the blue component was last seen in the −7.8 day
spectrum as a weak feature on the blue wing of the line, and in
SN 2001el it may be still present in the −2 day spectrum. The
peculiar flat-bottom line shape in the early spectra of SN 2001el
and SN 1990N is thus due to the blue component extending over
a larger velocity interval compared to other SNe. The −9 day
spectrum of SN 1999ee on the other hand, has a stronger blue
component such that the line is asymmetric with an extended
red wing. Note that Mazzali (2001) and Mazzali et al. (2005b)
find that a two-component model is needed to explain the pe-
culiar Si ii λ6355 line shape in SN 1990N and SN 1999ee, the
high-velocity (HV) component being carbon/silicon and a thin
pure Si shell, respectively. It is also clear that the early-time evo-
lution of the blueshift of the line-profile minimum will be largely
determined by the evolution of relative strength of the two com-
ponents, and therefore will be very difficult to interpret.
Mattila et al. (2005) suggest that the flat-bottomed shape of
Si ii λ6355 in SN 2001el and its disappearance over a few days
can be explained by the effects of scattering within a thin re-
gion moving at the continuum photospheric velocity, thus re-
quiring no absorbing HV material to produce the line shape.
SN 2003du
-12.8
-10.9
SN 1994D
-12.0
-11.0
-10.2
SN 1990N
SN 2001el
SN 1999ee
SN 2005cg
-10.9
SN 2003du
Si II 3850?
-12.0
-11.0
-10.2
Si II    3850?
SN 1994D
SN 1998bu
Si II 3850?
SN 2001el -9
-20000 0
-10.9
SN 2003du
-20000 0
Velocity [km s-1]
SN 1994D
SN 2001el
-20000 0
SN 1998bu
Fig. 15. Comparison of the evolution of Si ii λ6355, Ca ii H&K and Ca ii
IR3 lines in SN 2003du with those of other normal SNe Ia.
Quimby et al. (2006) argue that the triangular shape of the pro-
file in SN 2005cg with an extended blue wing (see, Fig. 15) may
be due to absorption by Si in the HV part of the ejecta. The
line profile may be reproduced if the Si abundance slowly de-
creases toward high velocities, which is typical for the delayed-
detonation models (Khokhlov, 1991). However, these both sug-
gestions may have difficulties to explain asymmetric line pro-
files with a stronger blue component as observed in SN 1999ee.
SN 1999ee is not unique. SN 2005cf, observed by the ESC with
daily sampling starting from 12 days before maximum (Garavini
et al., 2007), shows Si ii λ6355 line that consists of two dis-
tinct components with profile evolution similar to SN 1999ee.
It is therefore likely that the ”peculiar” profiles in SN 2001el,
SN 1990N and SN 2005cg are just snapshots of this common
16 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
evolutionary pattern. In addition, if more SNe Ia like SN 2005cf
and SN 1999ee are found, the suggestion of Quimby et al. (2006)
that the SNe Ia with a flat-bottomed Si ii λ6355 line may consti-
tute a separate sub-class of SNe Ia, possibly produced from dif-
ferent progenitors and/or explosion models can be ruled out.
In the −11 day spectrum of SN 2003du the Ca ii H&K
line is a broad, single absorption with high velocity of
∼ −21000 km s−1. In the −7.8 days spectrum another, less
blueshifted Ca ii H&K component is also visible at velocity of
∼ −10000 km s−1. In the subsequent spectra, the HV compo-
nent decreases in strength, while the low-velocity one grows
stronger. Qualitatively the same evolution of also observed in
SN 1994D. In the near maximum spectra, the HV component
is much weaker, if present at all, in SN 1994D and SN 1998bu
than in SN 2003du and SN 2001el. It can be seen in Fig 15 that
the strength of the HV component in SN 1994D decreases faster
than in SN 2003du and SN 2001el, thus qualitatively following
the evolution of the Si ii λ6355 HV component. On the other
hand, SN 1998bu either lacked HV components altogether, or
they disappeared faster than in SN 1994D. The evolution of the
Ca ii IR3 line is shown for few epochs only, but it is evident
that a strong HV component with velocity of ∼ −21000 km s−1
is also present and that this component disappears at different
time, earliest in SN 1994D, followed by SN 2003du, and latest
in SN 2001el. It is also interesting to note that there is a segrega-
tion of SNe Ia according to Ca iiH&K line profile: (i) SNe with a
single-component line at all epochs, SN 2004S (Krisciunas et al.,
2007), SN 1999ee and SN 2002bo being examples, and (ii) SNe
like SN 2003du and SN 1994D with double-component line af-
ter maximum. In SN 1994D the blue component of the post-
maximum Ca ii H&K-split is already visible in the −9 spectrum
as a weak feature superimposed on the broad HV component,
while in SN 2003du it becomes apparent only around maximum,
possibly because the HV component remains visible longer than
in SN 1994D. Possible identification for this feature is Si ii λ3850
(Nugent et al., 1997; Lentz et al., 2000), which is also supported
by the identification of strong Si ii λ3850 line in the early spec-
trum of SN 2004dt (Wang et al., 2006).
Due to severe line blending it is difficult to quantify the
strength of the HV components at different epochs. However, the
qualitative comparison strongly suggests that the strength of the
HV components in the Si ii λ6355, Ca ii H&K and Ca ii IR3 line
in given SN are correlated and evolve similarly. The HV features
in the Ca ii lines are stronger and more separated from the lower-
velocity components than in the Si ii λ6355 line. Comprehensive
spectral modeling of the line profiles evolution is therefore
needed to verify the two-component hypothesis for Si ii λ6355
and further investigate the HV features (e.g. Mazzali et al.,
2005b). Such an analysis of the SN 2003du spectra will be pre-
sented elsewhere. Currently, there is no consensus on the origin
of the HV features. Interaction of the ejecta with circumstellar
matter close to the SN (e.g. Gerardy et al., 2004) or the clumpy
ejecta structure found in some explosion models (e.g., Mazzali
et al., 2005b; Plewa et al., 2004; Kasen & Plewa, 2005) could
cause the observed HV features. The continuum polarization in
SNe Ia is typically low, but much higher polarization across the
lines including the HV features is often observed, which favors
the clumpy ejecta model rather than a global asymmetry (Wang
et al., 2003a, 2006, 2007; Leonard et al., 2005). The HV features
may thus carry information about the 3D structure of the ejecta
and the environment close to the SN explosion site. Modeling
of time sequences of flux and polarization spectra (e.g., Kasen
et al., 2003; Thomas et al., 2004; Wang et al., 2007) may al-
low us to recover this information and help to impose additional
constraints on the SN Ia explosion and progenitor models.
5. Summary
We present an extensive set of optical and NIR observations of
the bright nearby Type Ia SN 2003du. The observations started
13 days before B-band maximum light, and continued for 480
days after with exceptionally good sampling. The optical pho-
tometry was performed after the background contamination
from the host galaxy had been removed by subtraction of tem-
plate images. The photometry was obtained using a number of
instruments with different filter responses. In order to properly
account for deviations from the standard system responses, the
optical photometry was calibrated by applying S-corrections.
Our observations show that the spectral and photometric
evolution of SN 2003du in both, optical and NIR wavelengths,
closely follow that of the normal SNe Ia. The luminosity decline
rate parameter ∆m15 is found to be 1.02 ±0.05, the ratio between
the depth of the Si ii λ5972 and λ6355 linesR(Si ii) = 0.22 ±0.02
and the velocity of the Si ii λ6355 line is ∼ −10000 km s−1
around maximum light. The analysis of the uvoir light curve sug-
gests that ∼ 0.6− 0.8 M⊙ of
56Ni was synthesized during the ex-
plosion. All this indicates an average normal SN Ia. We also find
that SN 2003du was unreddened in its host galaxy. This property
is important for better understanding of the intrinsic colors of
SNe Ia in order to obtain accurate estimates of the dust extinction
to the high-redshift SNe Ia, which is one of the major systematic
uncertainties in their cosmological use. SN 2003du also showed
strong high-velocity features in Ca ii H&K and Ca ii IR3 lines,
and possibly in Si ii λ6355. The excellent temporal coverage al-
lowed us to compare the time evolution of the line profiles with
other well-observed SNe Ia and we found evidence that the pe-
culiar pre-maximum evolution of Si ii λ6355 line in many SNe Ia
is due to the presence of two blended absorption components.
The well-sampled and carefully calibrated data set we
present is a significant addition to the well-observed SNe Ia and
the data will be made publicly available for further analysis. For
example comprehensive modeling of the extensive spectral data
set, e.g. by the abundance tomography method (Stehle et al.,
2005), may eventually help to achieve a better understanding of
the physics of SNe Ia explosions and their progenitors.
Acknowledgements. This work is partly supported by the European
Community’s Human Potential Program “The Physics of Type Ia Supernovae”,
under contract HPRN-CT-2002-00303. V.S. and A.G. would like to thank the
Göran Gustafsson Foundation for financial support. The work of D.Yu.T. and
N.N.P. was partly supported by the grant RFBR 05-02-17480. The work of S.M.
was supported by a EURYI scheme award.
This work is based on observations collected at the Italian Telescopio
Nazionale Galileo (TNG), Isaac Newton (INT) and William Herschel (WHT)
Telescopes, and Nordic Optical Telescope (NOT), all located at the Spanish
Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de
Canarias (La Palma, Spain), the 1.82m and 1.22m telescopes at Asiago (Italy),
the 2.2m and 3.5m telescopes at Calar Alto (Spain), the United Kingdom
Infrared Telescope (UKIRT) at Hawaii and the 60-cm telescope of the Beijing
Astronomical Observatory (China). We thank the support astronomers of these
telescopes for performing part of the observations. We also thank the director of
the Calar Alto Observatory Roland Gredel for allocating additional time at the
2.2m telescope in May 2003.
We thank all observers that gave up part of their time to observe SN 2003du.
Thomas Augusteijn and Amanda Djupvik are acknowledged for observing dur-
ing two technical nights at the NOT. Observations were also obtained at the
NOT during a student training course in Observational Astronomy provided
by Stockholm Observatory and the NorFA Summer School in Observational
Astronomy. We thank Geir Oye for excellent support and close collaboration dur-
ing this course. We also thank O.A.Burkhanov, S.Yu.Shugarov and I.M.Volkov
for carrying out observations at Maidanak, Slovakia, Moscow and Crimea. We
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 17
thank Cecilia Kozma for making available to us her late-time light curve mod-
els. We thank Aaron Barth for providing us with the spectra of SN 1994D col-
lected by the Alexei Filippenko group at UC Berkeley, and the people who did
the observations: Aaron Barth, Alexei Filippenko, Tomas Matheson, Xiaoming
Fan, Michael Gregg, Vesa Junkkarinen, Brian Espey, Matt Lehnert, Lee Armus,
Graeme Smith, Greg Wirth, David Koo, Abe Oren and Vince Virgilio. We thank
K. Motohara and the co-authors of Motohara et al. (2006) for providing us with
the unpublished late-time NIR magnitudes of SN 2003du.
This work has made use of the NASA/IPAC Extragalactic Database (NED),
the Lyon-Meudon Extragalactic Database (LEDA), NASA’s Astrophysics Data
System, the SIMBAD database operated at CDS, Strasbourg, France, data prod-
ucts from the Two Micron All Sky Survey and the SUSPECT supernova spectral
archive.
References
Alard, C. 2000, A&AS, 144, 363
Alard, C. & Lupton, R. H. 1998, ApJ, 503, 325
Anupama, G. C., Sahu, D. K., & Jose, J. 2005, A&A, 429, 667
Astier, P., Guy, J., Regnault, N., et al. 2006, A&A, 447, 31
Benetti, S., Cappellaro, E., Mazzali, P. A., et al. 2005, ApJ, 623, 1011
Benetti, S., Meikle, P., Stehle, M., et al. 2004, MNRAS, 348, 261
Bessell, M. S. 1990, PASP, 102, 1181
Bessell, M. S. 1995, PASP, 107, 672
Bessell, M. S., Castelli, F., & Plez, B. 1998, A&A, 333, 231
Branch, D., Garnavich, P., Matheson, T., et al. 2003, AJ, 126, 1489
Branch, D., Lacy, C. H., McCall, M. L., et al. 1983, ApJ, 270, 123
Branch, D. & Tammann, G. A. 1992, ARA&A, 30, 359
Branch, D., Thomas, R. C., Baron, E., et al. 2004, ApJ, 606, 413
Cappellaro, E., Mazzali, P. A., Benetti, S., et al. 1997, A&A, 328, 203
Colgate, S. A., Petschek, A. G., & Kriese, J. T. 1980, ApJ, 237, L81
Elias-Rosa, N., Benetti, S., Cappellaro, E., et al. 2006, MNRAS, 369, 1880
Filippenko, A. V. 1982, PASP, 94, 715
Filippenko, A. V. 1997, ARA&A, 35, 309
Garavini, G., Aldering, G., Amadon, A., et al. 2005, AJ, 130, 2278
Garavini, G., Folatelli, G., Goobar, A., et al. 2004, AJ, 128, 387
Garavini, G., Nobili, S., Taubenberger, S., et al. 2007, ArXiv Astrophysics e-
prints
Gerardy, C. L., Höflich, P., Fesen, R. A., et al. 2004, ApJ, 607, 391
Hamuy, M., Maza, J., Pinto, P. A., et al. 2002, AJ, 124, 417
Hamuy, M., Phillips, M. M., Maza, J., et al. 1995, AJ, 109, 1
Hamuy, M., Phillips, M. M., Suntzeff, N. B., et al. 1996, AJ, 112, 2391
Harris, W. E., Fitzgerald, M. P., & Reed, B. C. 1981, PASP, 93, 507
Hernandez, M., Meikle, W. P. S., Aparicio, A., et al. 2000, MNRAS, 319, 223
Hillebrandt, W. & Niemeyer, J. C. 2000, ARA&A, 38, 191
Hoeflich, P., Wheeler, J. C., & Thielemann, F. K. 1998, ApJ, 495, 617
Holschneider, M., Kronland-Martinet, R., Morlet, J., & Tchamitchian, P. 1989,
in Wavelets. Time-Frequency Methods and Phase Space, ed. J.-M. Combes,
A. Grossmann, & P. Tchamitchian, 286
Horne, K. 1986, PASP, 98, 609
Hunt, L. K., Mannucci, F., Testi, L., et al. 1998, AJ, 115, 2594
Iwamoto, K., Nakamura, T., Nomoto, K., et al. 2000, ApJ, 534, 660
Jeffery, D. J., Leibundgut, B., Kirshner, R. P., et al. 1992, ApJ, 397, 304
Jha, S., Garnavich, P. M., Kirshner, R. P., et al. 1999, ApJS, 125, 73
Jha, S., Kirshner, R. P., Challis, P., et al. 2006a, AJ, 131, 527
Jha, S., Riess, A. G., & Kirshner, R. P. 2006b, ArXiv Astrophysics e-prints
Karp, A. H., Lasher, G., Chan, K. L., & Salpeter, E. E. 1977, ApJ, 214, 161
Kasen, D., Nugent, P., Wang, L., et al. 2003, ApJ, 593, 788
Kasen, D. & Plewa, T. 2005, ApJ, 622, L41
Kasen, D. & Woosley, S. E. 2007, ApJ, 656, 661
Khokhlov, A., Mueller, E., & Hoeflich, P. 1993, A&A, 270, 223
Khokhlov, A. M. 1991, A&A, 245, 114
Kirshner, R. P., Jeffery, D. J., Leibundgut, B., et al. 1993, ApJ, 415, 589
Knop, R. A., Aldering, G., Amanullah, R., et al. 2003, ApJ, 598, 102
Kotak, R., Meikle, W. P. S., Pignata, G., et al. 2005, A&A, 436, 1021
Kotak, R., Meikle, W. P. S., & Rodriguez-Gil, P. 2003, IAU Circ., 8122, 3
Krisciunas, K., Garnavich, P. M., Stanishev, V., et al. 2007, AJ, 133, 58
Krisciunas, K., Hastings, N. C., Loomis, K., et al. 2000, ApJ, 539, 658
Krisciunas, K., Phillips, M. M., Stubbs, C., et al. 2001, AJ, 122, 1616
Krisciunas, K., Phillips, M. M., & Suntzeff, N. B. 2004a, ApJ, 602, L81
Krisciunas, K., Phillips, M. M., Suntzeff, N. B., et al. 2004b, AJ, 127, 1664
Krisciunas, K., Suntzeff, N. B., Candia, P., et al. 2003, AJ, 125, 166
Krisciunas, K., Suntzeff, N. B., Phillips, M. M., et al. 2004c, AJ, 128, 3034
Lair, J. C., Leising, M. D., Milne, P. A., & Williams, G. G. 2006, AJ, 132, 2024
Landolt, A. U. 1992, AJ, 104, 340
Leibundgut, B., Kirshner, R. P., Filippenko, A. V., et al. 1991, ApJ, 371, L23
Lentz, E. J., Baron, E., Branch, D., Hauschildt, P. H., & Nugent, P. E. 2000, ApJ,
530, 966
Leonard, D. C., Li, W., Filippenko, A. V., Foley, R. J., & Chornock, R. 2005,
ApJ, 632, 450
Majewski, S. R., Kron, R. G., Koo, D. C., & Bershady, M. A. 1994, PASP, 106,
Marion, G. H., Höflich, P., Vacca, W. D., & Wheeler, J. C. 2003, ApJ, 591, 316
Marion, G. H., Höflich, P., Wheeler, J. C., et al. 2006, ApJ, 645, 1392
Mattila, S., Lundqvist, P., Sollerman, J., et al. 2005, A&A, 443, 649
Mazzali, P. A. 2001, MNRAS, 321, 341
Mazzali, P. A., Benetti, S., Altavilla, G., et al. 2005a, ApJ, 623, L37
Mazzali, P. A., Benetti, S., Stehle, M., et al. 2005b, MNRAS, 357, 200
Mazzali, P. A., Iwamoto, K., & Nomoto, K. 2000, ApJ, 545, 407
Mazzali, P. A. & Lucy, L. B. 1998, MNRAS, 295, 428
Mazzali, P. A., Nomoto, K., Cappellaro, E., et al. 2001, ApJ, 547, 988
Mazzali, P. A. & Podsiadlowski, P. 2006, MNRAS, 369, L19
Meikle, W. P. S. 2000, MNRAS, 314, 782
Meikle, W. P. S., Cumming, R. J., Geballe, T. R., et al. 1996, MNRAS, 281, 263
Milne, P. A., The, L.-S., & Leising, M. D. 1999, ApJS, 124, 503
Motohara, K., Maeda, K., Gerardy, C. L., et al. 2006, ApJ, 652, L101
Nobili, S., Goobar, A., Knop, R., & Nugent, P. 2003, A&A, 404, 901
Nomoto, K., Thielemann, F.-K., & Yokoi, K. 1984, ApJ, 286, 644
Nugent, P., Baron, E., Branch, D., Fisher, A., & Hauschildt, P. H. 1997, ApJ,
485, 812
Nugent, P., Kim, A., & Perlmutter, S. 2002, PASP, 114, 803
Nugent, P., Phillips, M., Baron, E., Branch, D., & Hauschildt, P. 1995, ApJ, 455,
L147+
Pastorello, A., Mazzali, P. A., Pignata, G., et al. 2007a, ArXiv Astrophysics e-
prints
Pastorello, A., Taubenberger, S., Elias-Rosa, N., et al. 2007b, MNRAS, 161
Patat, F., Benetti, S., Cappellaro, E., et al. 1996, MNRAS, 278, 111
Pauldrach, A. W. A., Duschinger, M., Mazzali, P. A., et al. 1996, A&A, 312, 525
Peebles, P. J. & Ratra, B. 2003, Reviews of Modern Physics, 75, 559
Perlmutter, S., Aldering, G., Goldhaber, G., et al. 1999, ApJ, 517, 565
Phillips, M. M. 1993, ApJ, 413, L105
Phillips, M. M., Lira, P., Suntzeff, N. B., et al. 1999, AJ, 118, 1766
Pignata, G., Benetti, S., Buson, L., et al. 2005, in ASP Conf. Ser. 342: 1604-
2004: Supernovae as Cosmological Lighthouses, ed. M. Turatto, S. Benetti,
L. Zampieri, & W. Shea, 266
Pignata, G., Patat, F., Benetti, S., et al. 2004, MNRAS, 355, 178
Pinto, P. A. & Eastman, R. G. 2000, ApJ, 530, 757
Plewa, T., Calder, A. C., & Lamb, D. Q. 2004, ApJ, 612, L37
Prieto, J. L., Rest, A., & Suntzeff, N. B. 2006, ApJ, 647, 501
Pskovskii, I. P. 1977, Soviet Astronomy, 21, 675
Quimby, R., Höflich, P., Kannappan, S. J., et al. 2006, ApJ, 636, 400
Riess, A. G., Filippenko, A. V., Challis, P., et al. 1998, AJ, 116, 1009
Riess, A. G., Li, W., Stetson, P. B., et al. 2005, ApJ, 627, 579
Riess, A. G., Press, W. H., & Kirshner, R. P. 1995, ApJ, 445, L91
Riess, A. G., Strolger, L.-G., Casertano, S., et al. 2007, ApJ, 659, 98
Riess, A. G., Strolger, L.-G., Tonry, J., et al. 2004, ApJ, 607, 665
Röpke, F. K., Gieseler, M., Reinecke, M., Travaglio, C., & Hillebrandt, W. 2006,
A&A, 453, 203
Röpke, F. K. & Hillebrandt, W. 2004, A&A, 420, L1
Rudy, R. J., Lynch, D. K., Mazuk, S., et al. 2002, ApJ, 565, 413
Ruiz-Lapuente, P. & Spruit, H. C. 1998, ApJ, 500, 360
Salvo, M. E., Cappellaro, E., Mazzali, P. A., et al. 2001, MNRAS, 321, 254
Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ, 500, 525
Schwartz, M. & Holvorcem, P. R. 2003, IAU Circ., 8121, 1
Sollerman, J., Lindahl, J., Kozma, C., et al. 2004, A&A, 428, 555
Spyromilio, J., Gilmozzi, R., Sollerman, J., et al. 2004, A&A, 426, 547
Stehle, M., Mazzali, P. A., Benetti, S., & Hillebrandt, W. 2005, MNRAS, 360,
Stetson, P. B. 2000, PASP, 112, 925
Stritzinger, M., Hamuy, M., Suntzeff, N. B., et al. 2002, AJ, 124, 2100
Stritzinger, M. & Leibundgut, B. 2005, A&A, 431
Stritzinger, M., Mazzali, P. A., Sollerman, J., & Benetti, S. 2006, A&A, 460, 793
Stritzinger, M., Suntzeff, N. B., Hamuy, M., et al. 2005, PASP, 117, 810
Suntzeff, N. B. 1996, in IAU Colloq. 145: Supernovae and Supernova Remnants,
ed. R. McCray & Z. Wang, 41
Suntzeff, N. B. 2000, in American Institute of Physics Conference Series, ed.
S. S. Holt & W. W. Zhang, 65–74
Thomas, R. C., Branch, D., Baron, E., et al. 2004, ApJ, 601, 1019
Timmes, F. X., Brown, E. F., & Truran, J. W. 2003, ApJ, 590, L83
Tokunaga, A. T., Simons, D. A., & Vacca, W. D. 2002, PASP, 114, 180
Umeda, H., Nomoto, K., Kobayashi, C., Hachisu, I., & Kato, M. 1999, ApJ, 522,
van Dokkum, P. G. 2001, PASP, 113, 1420
Wade, R. A. & Horne, K. 1988, ApJ, 324, 411
18 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
Wang, L., Baade, D., Höflich, P., et al. 2003a, ApJ, 591, 1110
Wang, L., Baade, D., Höflich, P., et al. 2006, ApJ, 653, 490
Wang, L., Baade, D., & Patat, F. 2007, Science, 315, 212
Wang, L., Goldhaber, G., Aldering, G., & Perlmutter, S. 2003b, ApJ, 590, 944
Wells, L. A., Phillips, M. M., Suntzeff, B., et al. 1994, AJ, 108, 2233
Wheeler, J. C., Hoeflich, P., Harkness, R. P., & Spyromilio, J. 1998, ApJ, 496,
Wood-Vasey, W. M., Miknaitis, G., Stubbs, C. W., et al. 2007, ArXiv
Astrophysics e-prints
Appendix A: S-corrections
A.1. Photometric systems responses
The most important ingredient for computing S-corrections is
the accurate knowledge of the object SED and the response of
the instruments used. Pignata et al. (2004) have calculated the
responses of most of the instruments used by the ESC. However,
we repeated the process for the 5 instruments most frequently
used to observe SN 2003du: AFOSC at Asiago 1.82m telescope,
DOLORES at TNG, ALFOSC at NOT, CAFOS at Calar Alto
2.2m telescope and BAO 60-cm telescope imager, using the new
extensive spectrophotometry of Landolt stars in Stritzinger et al.
(2005). The first four of the five instruments are combined spec-
trographs/imagers with design that allows the grisms, the slits
and the imaging filters to be inserted into the light beam simul-
taneously. This made possible to measure the filter transmissions
in situ as the filters are mounted in the instrument and used dur-
ing the photometric observations. This measurement is straight-
forward and consists of taking spectral flat-fields with and with-
out the filter in the beam. The flat taken with the filter is divided
by the one taken without, giving the filter transmission. Before
doing this, the bias and any reflected light present was carefully
removed. The latter can be important in the blue part of the spec-
trum where the sensitivity of the system is low and the scattered
light can be a significant fraction of the useful signal; this can af-
fect the measured transmission. The wavelength calibration was
done with arc-lamp spectra taken without the filter in the beam.
When filters are introduced in the beam small shifts of the wave-
length solution can be expected. After the measurements we
checked this for few filters at AFOSC at Asiago 1.8m telescope
and did indeed find shifts of a few pixels. Hence, the measured
filter transmissions might be shifted by up to 20–30 Å, but the
shape is accurately determined. Generally, we found good agree-
ment with the filter transmissions available from the instrument
web-pages. However, we found significant discrepancies for the
Calar Alto 2.2m + CAFOS B and I filters, and minor differences
for the TNG+DOLORS I-band. For the U-bands we used the
transmissions available from the instrument web-pages. For the
BAO 60-cm telescope the filter transmissions specified by the
manufacturer were used.
The total system responses were computed by multiplying
the filter transmissions by (a) the CCD quantum efficiency (QE),
(b) the reflectivity of at least two aluminum surfaces, (c) the
continuum transmission of the Earth atmosphere at airmass one
(the extinction laws were provided by the observatories), and
(d) a telluric absorption spectrum, which we derived from the
spectrophotometric standards observed at WHT close to airmass
one. The lens and window transmissions were not included be-
cause this information was unavailable. Synthetic magnitudes
were calculated from Stritzinger et al. (2005) spectrophotometry
of Landolt standard stars, msyn = −2.5 log
f phot
(λ)Rnat(λ)dλ
The difference between the synthetic and the observed photome-
try was fitted as a function of the observed color indices to com-
pute synthetic color-terms (ctsyn), e.g. for B we have
Bstd − Bsyn = ctsyn(Bstd − V std) + const. (A.1)
For the VRI-bands, the ctsyn’s were close to the observed ones
ctobs. In some cases small differences exceeding the uncertainty
were accounted for by shifting the filter transmissions until ctsyn
matched ctosb. Small shifts of up to ∼ 20 − 30 Å were required.
These discrepancies could easily have arisen from the way in
which the transmissions were determined, as discussed above.
For the U and B-bands however, we found large differences
which would have required an unacceptably large shift to cor-
rect for them. The synthetic U and B bands were always too blue.
This is, to some extent, to be expected because the neglected op-
tical elements like lenses or windows, anti-reflection and other
coatings will tend to reduce the system sensitivity shortward of
∼4000 Å. The uncertainty in the CCD QEs and the extinction
laws may also contribute to this effect. To account for the net
effect of these uncertainties we modified the U and B bands by
multiplying them with a smooth monotonic function of wave-
length so that ctsyn matched ctobs. We used the Sigmoid function
F(λ; λ0,∆) =
1 + exp(−(λ − λ0)/∆)
, (A.2)
that changes smoothly from 0 to 1. The parameters λ0 and ∆
control the position and the width of the transition; for small
∆ the Sigmoid function approaches a Heaviside step function
at λ0. We proceeded as follows: λ0 and ∆ were varied in the
wavelength intervals 3200–4200Å and 100–500 Å, respectively,
and the set of parameters that brought the synthetic U and B-
band color-terms into accord with the observed ones was chosen.
Note that independent modification of U and B results in degen-
eracy in the (λ0,∆) parameter space, and it was only when the
U and B-bands were considered together that an unique solution
for λ0 and ∆ could be obtained. As standard Johnson-Cousins
system responses we use the Bessell (1990) filters but following
Stritzinger et al. (2005) we first modified them so that they could
be used with photon fluxes and included the telluric absorptions.
Small shifts were also applied to account for the small color-
terms that are noticeable when compared with the Landolt pho-
tometry. Bessell (1995) suggested correcting Landolt photome-
try to bring it into the original Cousins system. The synthetic
photometry with the original Bessell filters does match the cor-
rected magnitudes. However, for sake of comparability with the
existing SN photometry, we use the original Landolt photometry
and modify the Bessell filters so that the synthetic color-terms
are zero. The constant terms derived from the fits with Eq. A.1
are the filter zero-points for synthetic photometry. The constant
in Eq. 2 is the difference between the zero-point for the Bessell
and natural passbands.
The reconstructed bands are shown in Fig. A.1 together with
the modified Bessell filters, demonstrating the variety of pass-
bands one may encounter at different telescopes. Note particu-
larly the non-standard form of the Calar Alto I-band and NOT
R-band. We note that the reconstructed responses should be re-
garded only as approximations of the real responses. A given
passband can be modified in many ways to match the observed
and the synthetic color-term, and we would consider the pro-
cedure we used as the most appropriate one given the available
information. We also note that fitting the U-band synthetic color-
term is ambiguous. Because of the Balmer discontinuity even
small deviation from the Bessell passband changes U std − U syn
such that it needs no longer be a simple linear function of
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 19
4000 6000 8000 10000
Wavelength [Å]
modified Bessell Asiago            TNG             NOT             Calar Alto                BAO
U          B                V            R                                     I
Fig. A.1. Reconstructed system responses for the five instruments studied compared to the modified Bessell passbands.
U std−Bstd. This also affects the derivation of the observed color-
terms and as a result the U-band photometry should be in general
considered significantly less accurate than other bands.
A.2. Computing the S-corrections
We used our spectra obtained earlier than 110 days after max-
imum, and spectra from Gerardy et al. (2004) and Anupama
et al. (2005) to compute the S-corrections and to transform
the BVRI photometry of SN 2003du into the Johnson-Cousins
system. The TNG, Calar Alto and BAO I-bands extend out to
1.1 µm and to compute the S-corrections, we also used our NIR
spectra of SN 2003du (Sec. 2.3). To compute the BAO I-band S-
corrections between +30 and +63 days we also used NIR spectra
of SN 1999ee (Hamuy et al., 2002) and SN 2000ca (Stanishev et
al., in preparation) taken at ∼ +40 days. The U-band could not
be S-corrected because no UV spectra of SN 2003du were avail-
able.
The relative spectrophotometry of SN 2003du was not al-
ways sufficiently accurate for the purpose of computing S-
corrections. It was thus necessary to slightly modify some of
the spectra so that the synthetic photometry with the modified
Bessell BVRI bands matched the observed one. To achieve that,
the spectra were multiplied by a smooth correction function de-
termined by fitting the ratio between the observed and the syn-
thetic fluxes. When the ratio varied monotonically with wave-
length, a second-order polynomial was used. When a more com-
plex function was required, a spline fit was used. At the first it-
eration the synthetic magnitudes were compared with the linear
color-term corrected magnitudes of SN 2003du, and the spectra
were only modified if the observed and the synthetic color in-
dices differed by more than 0.05 mag for B − V and V − R, and
0.1 mag for V − I. These corrected spectra were used to compute
S-corrected photometry of SN 2003du. The flux correction of the
spectra was then repeated using the S-corrected rather than the
color-term corrected photometry. Spectra were only corrected if
the color discrepancies were greater than 0.03 mag for B − V
and V − R, or 0.05 mag for V − I. New S-corrected photome-
try was then computed and the process repeated to obtain the
final S-corrected photometry and calibrated spectra. A number
of spectra have a wavelength coverage that only allows B and V
synthetic magnitudes to be computed. In these cases, only a sim-
ple linear correction was applied to match the observed B and V
magnitudes.
We note that because the instrumental responses are fairly
close to those of Bessell filters, the S-corrections are almost en-
tirely determined by the SN spectral features and are practically
insensitive to small changes of the SN colors. It was found that
the initial correction of the spectra yielded spectrophotometry
which was already accurate to a few per cent and that the subse-
quent iterations had very little effect on the final calibrated pho-
tometry. We therefore conclude that the few percent uncertain-
ties in the spectrophotometry, which might have arisen from the
way the spectra were corrected, should have little effect on the
final photometry.
List of Objects
‘SN 2003du’ on page 1
‘SN 2003du’ on page 1
‘UGC 9391’ on page 1
‘SN 2003du’ on page 1
‘SN 2003du’ on page 1
‘SN 2003du’ on page 2
‘UGC 9391’ on page 2
‘SN 2003du’ on page 2
‘SN 2002bo’ on page 2
‘SN 2002dj’ on page 2
‘SN 2002er’ on page 2
‘SN 2003cg’ on page 2
‘SN 2004eo’ on page 2
‘SN 2005cf’ on page 2
‘SN 2003du’ on page 2
‘SN 2003du’ on page 2
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22 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
Table 3. Optical photometry SN 2003du. The measurements on the dates marked with ”∗” and all U magnitudes are not S-corrected.
Date (UT) Phase [day] JD U B V R I Telescope
2003-04-25 −11.0 2452755.39 · · · 14.737 (0.018) 14.854 (0.014) 14.728 (0.010) 14.798 (0.017) AS1.8
2003-04-25 −10.8 2452755.61 14.382 (0.011) 14.629 (0.010) 14.774 (0.010) 14.672 (0.010) 14.756 (0.021) NOT
2003-04-29 −7.3 2452759.06 · · · 13.974 (0.014) 14.072 (0.022) 13.963 (0.015) 14.052 (0.017) BAO
2003-04-30 −6.2 2452760.17 · · · 13.820 (0.024) 13.920 (0.012) 13.852 (0.010) 13.936 (0.024) BAO
2003-04-30 −5.8 2452760.54 13.193 (0.034) 13.719 (0.018) 13.860 (0.010) 13.754 (0.010) 13.921 (0.021) TNG
2003-05-02 −4.0 2452762.38 13.077 (0.015) 13.589 (0.021) 13.712 (0.027) 13.639 (0.022) 13.834 (0.023) TNG
2003-05-04 −1.9 2452764.46 · · · 13.496 (0.010) 13.614 (0.018) 13.592 (0.010) 13.841 (0.010) AS1.8
2003-05-05 −1.0 2452765.41 · · · 13.489 (0.012) 13.595 (0.019) 13.569 (0.010) 13.857 (0.011) AS1.8
2003-05-06 +0.0 2452766.40 · · · 13.489 (0.019) 13.566 (0.025) 13.575 (0.011) 13.870 (0.010) AS1.8
2003-05-07 +1.1 2452767.51 · · · 13.506 (0.015) 13.575 (0.014) 13.590 (0.018) 13.927 (0.016) AS1.8
2003-05-09 +3.1 2452769.51 · · · 13.566 (0.010) 13.587 (0.021) 13.600 (0.010) 14.009 (0.010) AS1.8
2003-05-10 +4.2 2452770.61 13.234 (0.014) 13.605 (0.010) 13.620 (0.016) 13.600 (0.010) 13.982 (0.016) CA2.2
2003-05-11 +5.1 2452771.51 13.316 (0.040) 13.643 (0.011) 13.642 (0.017) · · · 14.017 (0.010) CA2.2
2003-05-13 +7.2 2452773.59 13.597 (0.021) 13.764 (0.010) 13.712 (0.010) 13.786 (0.011) 14.205 (0.018) NOT
2003-05-14 +8.2 2452774.56 13.651 (0.017) 13.845 (0.011) 13.758 (0.010) 13.838 (0.010) 14.271 (0.010) NOT
2003-05-15 +9.1 2452775.44 13.749 (0.017) 13.908 (0.010) 13.795 (0.011) 13.908 (0.011) 14.352 (0.015) NOT
2003-05-16 +10.1 2452776.45 13.838 (0.021) 14.004 (0.014) 13.842 (0.010) 13.979 (0.010) 14.443 (0.011) NOT
2003-05-17 +10.7 2452777.08 · · · 14.066 (0.018) 13.862 (0.010) 14.040 (0.011) 14.448 (0.010) BAO
2003-05-22 +15.8 2452782.20 · · · 14.596 (0.013) 14.186 (0.010) 14.342 (0.011) 14.588 (0.017) BAO
2003-05-23 +17.1 2452783.49 · · · 14.722 (0.023) 14.268 (0.028) 14.332 (0.012) 14.626 (0.031) AS1.8
2003-05-24 +18.0 2452784.42 · · · 14.833 (0.014) 14.302 (0.014) 14.350 (0.016) 14.611 (0.010) AS1.8
2003-05-25 +19.0 2452785.37 · · · 14.942 (0.012) 14.350 (0.013) 14.361 (0.012) 14.594 (0.010) AS1.8
2003-05-26 +20.0 2452786.38 · · · 15.043 (0.011) · · · · · · · · · CA2.2
2003-05-27 +21.0 2452787.45 15.144 (0.017) 15.146 (0.014) 14.463 (0.017) 14.392 (0.012) 14.464 (0.018) CA2.2
2003-05-29 +22.8 2452789.20 · · · · · · · · · 14.493 (0.031) 14.451 (0.014) BAO
2003-06-01 +26.1 2452792.51 15.809 (0.023) 15.648 (0.010) 14.724 (0.010) 14.453 (0.019) 14.410 (0.027) TNG
2003-06-06 +31.2 2452797.58 16.172 (0.033) 16.041 (0.011) 15.018 (0.014) 14.658 (0.010) 14.451 (0.019) TNG
2003-06-10 +34.7 2452801.06 · · · 16.363 (0.085) 15.223 (0.047) 14.881 (0.018) 14.540 (0.035) BAO
2003-06-14 +38.7 2452805.04 · · · · · · 15.477 (0.131) 15.140 (0.013) 14.829 (0.024) BAO
2003-06-15 +39.7 2452806.04 · · · 16.472 (0.036) 15.473 (0.011) 15.187 (0.018) 14.929 (0.018) BAO
2003-06-20 +45.1 2452811.51 · · · 16.606 (0.021) 15.676 (0.010) 15.415 (0.017) 15.265 (0.010) AS1.8
2003-06-26 +51.1 2452817.52 16.796 (0.023) 16.727 (0.011) 15.859 (0.015) 15.613 (0.011) 15.584 (0.022) TNG
2003-06-28 +52.7 2452819.04 · · · 16.745 (0.023) 15.892 (0.012) 15.679 (0.018) 15.633 (0.038) BAO
2003-06-30 +54.6 2452821.03 · · · 16.753 (0.039) 15.924 (0.018) 15.776 (0.032) 15.715 (0.039) BAO
2003-07-04 +58.7 2452825.06 · · · 16.835 (0.016) 16.046 (0.019) 15.874 (0.011) 15.920 (0.022) BAO
2003-07-05 +60.0 2452826.38 · · · · · · 16.088 (0.016) 15.926 (0.010) 16.026 (0.019) NOT
2003-07-08 +62.7 2452829.06 · · · · · · 16.159 (0.036) 16.010 (0.017) 16.096 (0.029) BAO
2003-07-08 +63.1 2452829.53 17.004 (0.026) 16.924 (0.011) 16.173 (0.010) 16.036 (0.011) 16.138 (0.017) NOT
2003-07-09 +63.7 2452830.06 · · · · · · · · · · · · 16.194 (0.045) BAO
2003-07-12∗ +66.8 2452833.19 · · · · · · 16.290 (0.020) 16.140 (0.020) 16.270 (0.030) MDK
2003-07-17 +72.0 2452838.33 · · · 17.082 (0.015) 16.410 (0.015) 16.275 (0.010) 16.477 (0.012) AS1.8
2003-08-01 +87.0 2452853.34 · · · 17.319 (0.010) 16.769 (0.011) 16.719 (0.011) 17.010 (0.011) AS1.8
2003-08-22 +108.0 2452874.40 · · · 17.618 (0.030) 17.266 (0.026) 17.309 (0.028) · · · AS1.8
2003-08-23 +109.0 2452875.37 · · · 17.688 (0.011) 17.281 (0.012) 17.379 (0.014) 17.756 (0.018) AS1.8
2003-09-16∗ +132.9 2452899.32 18.763 (0.079) 17.961 (0.022) 17.780 (0.021) 18.040 (0.023) 18.454 (0.075) CA2.2
2003-09-19∗ +136.0 2452902.38 18.844 (0.032) 18.059 (0.012) 17.851 (0.017) 18.077 (0.029) 18.329 (0.020) WHT
2003-09-26∗ +143.0 2452909.34 19.140 (0.072) 18.114 (0.021) 17.956 (0.043) 18.330 (0.062) 18.570 (0.067) CA2.2
2003-11-22∗ +199.2 2452965.62 · · · 18.660 (0.100) 18.670 (0.100) 19.090 (0.120) · · · CRM
2003-11-23∗ +200.3 2452966.63 · · · 18.990 (0.060) 18.930 (0.060) 19.210 (0.110) · · · CRM
2003-11-25∗ +202.2 2452968.61 · · · 18.900 (0.040) 18.950 (0.050) 19.330 (0.110) · · · CRM
2003-12-01∗ +208.3 2452974.63 · · · 19.020 (0.070) 19.090 (0.100) 19.370 (0.120) · · · CRM
2003-12-12∗ +220.4 2452986.75 20.688 (0.038) 19.304 (0.016) 19.313 (0.012) 19.899 (0.041) 19.673 (0.031) CA3.5
2003-12-19∗ +227.4 2452993.75 · · · 19.384 (0.010) 19.419 (0.011) 19.979 (0.044) 19.910 (0.033) CA3.5
2004-05-10∗ +370.2 2453136.62 · · · 21.476 (0.019) 21.453 (0.020) 22.202 (0.044) 21.192 (0.029) WHT
2004-05-11∗ +371.2 2453137.62 22.638 (0.079) 21.531 (0.011) 21.493 (0.018) 22.190 (0.028) 21.320 (0.030) WHT
2004-06-22∗ +413.4 2453179.54 · · · 22.100 (0.044) 22.010 (0.026) 23.010 (0.052) 21.720 (0.038) NOT
2004-08-11∗ +463.0 2453229.43 · · · 22.771 (0.027) 22.827 (0.026) · · · · · · NOT
2004-08-14∗ +466.0 2453232.39 · · · · · · · · · · · · 22.212 (0.048) TNG
AS1.8 – Asiago 1.82m + AFOSC; NOT – Nordic Optical Telescope + ALFOSC; CA2.2 – Calar Alto 2.2m + CAFOS; TNG – Telescopio
Nazionale Galileo + DOLORES; WHT – William Herschel Telescope + PFIP; CA3.5 – Calar Alto 3.5m + LAICA; BAO – Beijing Astronomical
Observatory 60cm + CCD; MDK – Maidanak Observatory 1.5m + SITe CCD; CRM – 60-cm Crimean reflector + CCD.

  An extensive set of optical and NIR photometry and low-resolution spectra the
Type Ia supernova (SN Ia) 2003du was obtained using a number of facilities. The
observations started 13 days before B-band maximum light and continued for 480
days with exceptionally good time sampling. The optical photometry was
calibrated through the S-correction technique.
  The UBVRIJHK light curves and the color indices of SN 2003du closely resemble
those of normal SNe Ia. SN 2003du reached a B-band maximum of 13.49 (+/-0.02)
mag on JD2452766.38 (+/-0.5). We derive a B-band stretch parameter of 0.988
(+/-0.003), which corresponds to dM15=1.02 (+/-0.05), indicative of a SN Ia of
standard luminosity. The reddening in the host galaxy was estimated by three
methods, and was consistently found to be negligible. We estimate a distance
modulus of 32.79 (+/-0.15) mag to the host galaxy, UGC 9391. The peak UVOIR
bolometric luminosity of 1.35(+/-0.20) 10^43 erg/s and Arnett's rule implies
that M(Ni56)=0.68 (+/-0.14)M_sun of Ni56 was synthesized during the explosion.
Modeling of the UVOIR bolometric light curve also indicates M(Ni56) in the
range 0.6-0.8 M_sun. The spectral evolution of SN 2003du at both optical and
NIR wavelengths also closely resembles normal SNe Ia. In particular, the Si II
ratio at maximum R(Si II)=0.22 (+/-0.02) and the time evolution of the
blueshift velocities of the absorption line minima are typical. The pre-maximum
spectra of SN 2003du showed conspicuous high-velocity features in the Ca II H&K
doublet and infrared triplet, and possibly in Si II 6355, lines. We compare the
time evolution of the profiles of these lines with other well-observed SNe Ia
and we suggest that the peculiar pre-maximum evolution of Si II 6355 line in
many SNe Ia is due to the presence of two blended absorption components.

Introduction
Type Ia supernovae (SNe Ia) form a relatively homogeneous
class of objects with only a small scatter in their observed ab-
solute peak magnitudes (∼ 0.3 mag). Moreover, their spectra
⋆ E-mail: vall@physto.se
and light curves are strikingly similar (e.g. Branch & Tammann,
1992). Theoretical investigations strongly suggest that SNe Ia
are thermonuclear explosions of carbon/oxygen white dwarfs
(WD) with masses close to the Chandrasekhar limit ∼ 1.4M⊙
(for a review see Hillebrandt & Niemeyer, 2000). In the fa-
vored model, the WD mass grows via accretion from a com-
http://arxiv.org/abs/0704.1244v1
2 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
panion star until the mass reaches the Chandrasekhar limit and
the WD ignites at (or near) its center. The light curves of SNe Ia
are powered by the energy released from the decay of radioac-
tive 56Ni produced during the explosion (typically a few tenths
of M⊙) and its daughter nuclides, and the scatter of the abso-
lute magnitudes is mostly due to the different amounts of syn-
thesized 56Ni. However, it has been shown that the peak lumi-
nosity of SNe Ia correlates with the luminosity decline rate af-
ter maximum light; the slower the decline, the greater the peak
luminosity (Pskovskii, 1977; Phillips, 1993; Hamuy et al., 1995,
1996; Riess et al., 1995). After correcting for the empirical ”light
curve width – peak luminosity” relation and for the extinction
in the host galaxy, the dispersion of the SN Ia absolute peak
B magnitudes is ∼ 0.14 mag (Phillips et al., 1999). This prop-
erty combined with their high intrinsic luminosity (MV ≃ −19.2
mag), make SNe Ia ideal for measuring relative cosmological
distances.
Observations of SNe Ia out to a redshift of z ∼ 1.0 led to
the surprising discovery that the expansion of the Universe is
accelerating, and that ∼ 70% of the Universe consists of an
unknown constituent with effective negative pressure, dubbed
”dark energy” (Riess et al., 1998; Perlmutter et al., 1999; Knop
et al., 2003; Riess et al., 2004; Astier et al., 2006; Riess et al.,
2007; Wood-Vasey et al., 2007). Currently, the favored model
for dark energy is a non-zero positive cosmological constant Λ
(or vacuum energy), but more exotic models have also been pro-
posed (for a review see Peebles & Ratra, 2003). There are sev-
eral observational programs planned or in progress that aim to
discover and observe hundreds of SNe Ia up to z ∼ 1.7, with
the goal of measuring cosmological parameters with greatly im-
proved accuracy. This will enable distinctions to be made be-
tween the large number of proposed models for dark energy.
Although these programs will be able to greatly reduce the sta-
tistical uncertainties on the measured cosmological parameters,
the output will still be limited by systematic errors due to our
poor knowledge of some aspects of SNe Ia and their environ-
ment. Two of the major concerns are the possible evolution of
the brightness or colors of SNe Ia with redshift and the esti-
mation of the reddening in the host galaxy. There are indica-
tions that the amount of 56Ni synthesized during the explosion
is sensitive to the metallicity, carbon-to-oxygen (C/O) ratio and
the central density of the exploding WD (Hoeflich et al., 1998;
Umeda et al., 1999; Timmes et al., 2003; Röpke & Hillebrandt,
2004; Röpke et al., 2006), although based on three-dimensional
simulations Röpke & Hillebrandt (2004) and Röpke et al. (2006)
found that the C/O ratio has little effect on the 56Ni production.
These quantities may, however, evolve with redshift and might
therefore introduce some evolution of the observed SNe Ia prop-
erties. However, our poor knowledge of the details of the physics
of the explosion, the progenitor systems and how the WD mass
grows to the Chandrasekhar limit (e.g., Hillebrandt & Niemeyer,
2000)) prevents us from accurately estimating the magnitude of
the effect, and the extent to which it could affect the derived
cosmological parameters. The difficulties in accurately estimat-
ing the reddening in the SN host galaxies arise mostly from the
uncertainty in the intrinsic colors of SNe Ia (e.g., Nobili et al.,
2003) and the calibration of the photometry (Suntzeff, 2000),
combined with poor knowledge of the dust properties.
In this paper we present observations of the nearby Type
Ia SN 2003du. It was discovered by The Lick Observatory
and Tenagra Observatory Supernova Searches (Schwartz &
Holvorcem, 2003) in the nearby (recession velocity of 1914
km s−1) SBd galaxy UGC 9391 on 2003 April 22.4 UT. Kotak
et al. (2003) classified SN 2003du as a normal SN Ia at about
two weeks before maximum light and an intensive optical and
NIR observational campaign was initiated by the European
Supernova Collaboration (ESC). The optical and NIR observa-
tions were carried out until 466 and 30 days after B-band max-
imum light, respectively; throughout this paper we define the
phase of the supernova as the time in days from the B-band
maximum. The goal of the ESC is to make progress in our un-
derstanding of the physics of the thermonuclear SN explosions
by collecting and analyzing early-time observations of nearby
SNe Ia. Since 2002 the ESC has obtained via coordinated obser-
vations using a large number of telescopes optical and IR ob-
servations for 15 nearby SNe Ia. First results of the observations
have already been published (SN 2002bo – Benetti et al. 2004,
Stehle et al. 2005; SN 2002dj – Pignata et al. 2005; SN 2002er –
Pignata et al. 2004, Kotak et al. 2005; SN 2003cg – Elias-Rosa
et al. 2006; SN 2004eo – Pastorello et al. 2007a; SN 2005cf –
Pastorello et al. 2007b, Garavini et al. 2007; Benetti et al. 2005;
Mazzali et al. 2005a). Optical observations of SN 2003du have
also been presented by Gerardy et al. (2004), Anupama et al.
(2005) and Leonard et al. (2005).
2. Observations and data reduction
2.1. Optical spectroscopy
The optical spectroscopy log of SN 2003du is given in Table 1.
The spectra were reduced1 following the algorithm of (Horne,
1986). The images were first bias and flat-field corrected. The
1D spectra were then optimally extracted from the 2D images,
simultaneously identifying and removing the cosmic rays and
bad pixels. The spectra were wavelength calibrated using arc-
lamp spectra. The wavelength calibration was checked against
the night-sky emission lines and, when necessary, small addi-
tive corrections were applied. Spectrophotometric standard stars
were used to flux calibrate the SN spectra. Telluric absorp-
tion features were removed from the supernova spectra follow-
ing Wade & Horne (1988). On a number of nights two differ-
ent spectrometer settings were used to cover the whole optical
wavelength range, and the two spectra were combined into a
single spectrum. Most of the spectra have dispersion between
∼ 1 Å pixel−1 and ∼ 5 Å pixel−1, except for the few red spec-
tra taken at Asiago 1.82m telescope, which have a dispersion of
∼ 15 Å pixel−1 and one WHT spectrum with ∼ 0.23 Å pixel−1.
The spectra were obtained with the slit oriented along the
parallactic angle in order to minimize differential losses due to
atmospheric refraction (Filippenko, 1982). Nevertheless the rel-
ative flux calibration was not always sufficiently accurate and
the final flux calibration was achieved by slightly correcting the
spectra to match the observed photometry. This step was done
alongside the calibration of the photometry and is discussed in
detail in the Appendix.
2.2. Optical photometry
The optical photometric observations of SN 2003du were ob-
tained with a number of instruments equipped with broadband
UBVRI filters. The CCD images were bias and flat-field cor-
rected. Cosmic ray hits were identified and cleaned with the
1 All data reduction and calibration was done in IRAF and with
our own programs written in IDL. IRAF is distributed by the
National Optical Astronomy Observatories, which are operated by the
Association of Universities for Research in Astronomy, Inc., under co-
operative agreement with the National Science Foundation.
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 3
Table 1. Log of the optical spectroscopy
Date (UT) JD Phase Wavelength Telescopea
[day] range [Å]
2003 Apr 23 2452753.58 −12.8 4900-7500 INT
2003 Apr 25 2452755.43 −10.9 3450-10400 AS1.8
2003 Apr 25 2452755.58 −10.8 4250-7500 NOT
2003 Apr 28 2452758.54 −7.8 3200-7500 INT
2003 Apr 30 2452760.56 −5.8 3230-8060 TNG
2003 May 02 2452762.39 −4.0 3230-8060 TNG
2003 May 04 2452764.48 −1.9 3436-7776 AS1.8
2003 May 05 2452765.39 −1.0 3500-7776 AS1.8
2003 May 06 2452766.39 +0.0 3447-7776 AS1.8
2003 May 07 2452767.55 +1.2 3500-9590 AS1.8
2003 May 08 2452768.54 +2.2 5860-7060 AS1.2
2003 May 09 2452769.54 +3.2 3500-10010 AS1.8
2003 May 10 2452770.64 +4.3 3300-10000 CA2.2
2003 May 12 2452772.57 +6.2 4680-7017 AS1.2
2003 May 13 2452773.61 +7.2 3300-7200 NOT
2003 May 14 2452774.59 +8.2 3300-7200 NOT
2003 May 15 2452775.48 +9.1 3250-7200 NOT
2003 May 16 2452776.47 +10.0 3260-9800 NOT
2003 May 21 2452781.51 +15.1 3800-6130 AS1.2
2003 May 23 2452783.55 +17.2 3600-10100 AS1.8
2003 May 24 2452784.60 +18.2 4260-6595 AS1.2
2003 May 25 2452785.39 +19.0 3700-7776 AS1.8
2003 May 27 2452787.52 +21.1 3400-8830 CA2.2
2003 Jun 01 2452792.52 +26.1 3240-8060 TNG
2003 Jun 06 2452797.60 +31.2 3240-8060 TNG
2003 Jun 09 2452800.45 +34.1 3500-9500 WHT
2003 Jun 14 2452805.38 +39.0 3700-10000 WHT
2003 Jun 20 2452811.54 +45.2 3880-7770 AS1.8
2003 Jun 26 2452817.52 +51.1 3350-10000 WHT
2003 Jul 08 2452829.44 +63.1 3700-9850 NOT
2003 Jul 17 2452838.41 +72.0 3500-10000 WHT
2003 Jul 29 2452850.42 +84.0 3600-10000 WHT
2003 Aug 23 2452875.32 +108.9 3000-7820 AS1.8
2003 Sep 25 2452907.82 +141.4 3500-8800 CA2.2
2003 Nov 18 2452962.25 +195.9 4370-7050 WHTb
2003 Dec 01 2452975.70 +209.3 3000-7600 CA3.5
2003 Dec 13 2452987.72 +221.3 3500-8820 CA2.2
2004 Feb 02 2453038.71 +272.3 3800-8000 CA3.5
2004 May 17 2453143.30 +376.9 3500-8060 TNG
a AS1.8 = Asiago 1.82m + AFOSC; AS1.2 = Asiago 1.22m + B&C;
TNG = TNG 3.58m + DOLORES; NOT = NOT 2.6m + ALFOSC;
CA2.2 = Calar Alto 2.2m + CAFOS; CA3.5 = Calar Alto 3.5m +
MOSCA; WHT =WHT 4.2m + ISIS; INT = INT 2.5m + IDS
b average of spectra obtained on 17 and 18 Nov. 2003; these spec-
tra cover the ranges 4370–5220 Å and 6200–7050 Å with dispersion
0.23 Å pixel−1.
Laplacian detection algorithm of van Dokkum (2001). The ob-
servations consist of single exposures at early times and dithered
multiple exposures at late epochs. In the latter case, the images
in each filter were combined to form a single image. For the I-
band, we also corrected for fringing in the individual exposures.
The SN lies only 15′′ from the host galaxy nucleus, on a
complex background (Fig. 1). The background contamination
may significantly degrade the photometry, especially at late
epochs when the SN has faded considerably. The approach com-
monly used is to subtract the background using template galaxy
images without the SN, taken either before or a few years af-
ter the SN explosion. The galaxy template, preferably with bet-
ter seeing and signal-to-noise ratio (S/N) than the SN images, is
aligned with the SN image, convolved with a suitable kernel so
that the point-spread functions (PSF) of the two images are the
same, then scaled to match the flux level of the SN image and
Fig. 1. A B-band finding chart of SN 2003du with the comparison stars
labeled by numbers. The image was obtained 87 days after B-band max-
imum.
Table 2. Calibrated magnitudes of the local stars around SN 2003du.
The number in parentheses are the uncertainties in mmag.
Star U B V R I
1 13.864 (39) 13.848 (22) 13.309 (13) 12.960 (13) · · ·
2 15.004 (39) 14.920 (22) 14.310 (14) 13.911 (13) 13.624 (12)
3 16.562 (40) 16.428 (22) 15.792 (13) 15.400 (13) 15.077 (13)
4 16.930 (40) 17.024 (23) 16.462 (14) 16.113 (14) 15.792 (12)
5 18.261 (45) 17.611 (24) 16.251 (14) 15.258 (15) 14.117 (13)
6 18.254 (45) 17.909 (24) 17.011 (15) 16.478 (14) 16.012 (12)
7 17.660 (42) 17.552 (23) 16.893 (14) 16.468 (14) 16.129 (12)
8 17.114 (40) 16.993 (23) 16.307 (15) 15.829 (14) 15.504 (12)
9 17.806 (42) 17.951 (24) 17.518 (15) 17.179 (16) 16.875 (13)
10 17.809 (42) 18.092 (24) 17.675 (16) 17.357 (16) 17.057 (13)
11 17.775 (42) 17.586 (23) 16.874 (15) 16.418 (15) 16.107 (14)
12 18.328 (46) 18.636 (27) 18.158 (18) 17.799 (18) 17.487 (14)
subtracted. The SN flux can then be correctly measured on the
background-subtracted image.
Lacking pre-explosion observations of the host galaxy of
SN 2003du, we constructed template images using observations
which we obtained more than one year after SN maximum light.
The SN magnitudes were measured by PSF-fitting. The small
SN contribution was then subtracted and the images were visu-
ally inspected for over- or under-subtraction (none was noticed).
The best seeing images were then combined to form the tem-
plates. The subtraction of the host galaxy from the ”SN + host”
images was done with Alard’s (Alard & Lupton, 1998; Alard,
2000) optimal image subtraction software, slightly modified and
kindly made available to us by B. Schmidt. When using galaxy
templates built in this way, any improperly subtracted SN light
will introduce systematic errors into the subsequent photometry.
In the case of SN 2003du this should, however, be negligible be-
cause at the epochs used to build the templates, the SN was much
fainter than on the images to which the template subtraction was
applied (at least 2 mag fainter at +220 days and 4–5 mag fainter
over the first three months after maximum). Even if we conser-
vatively assume that the final templates still contained 20% of
4 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
the SN light, the error introduced would be at most 0.03 mag
at +220 days and clearly negligible during the first 3-4 months
after maximum.
The SN magnitudes were measured differentially with re-
spect to the field stars indicated with numbers in Fig. 1. The
instrumental magnitudes were measured by aperture photometry
for observations before September 2003 and by PSF fitting at the
later epochs. The magnitudes of the field stars were calibrated
for two photometric nights at the Nordic Optical Telescope –
May 15 and 16, 2003. On each night, the field of the globular
cluster M92 that includes the standard stars listed in Majewski
et al. (1994) was observed at four airmasses between 1.06 and
1.8. The BVRI magnitudes of the standard stars were taken from
(Stetson, 2000)2, while the U magnitudes were calculated from
the U − B values given in Majewski et al. (1994). The standard
star magnitudes were measured with PSF photometry and aper-
ture corrections were applied to convert the PSF magnitudes to
magnitudes in an aperture with a radius of five times the see-
ing. Following Harris et al. (1981), all measured magnitudes
were fitted simultaneously (with 3σ clipping) to derive linear
transformation equations, with the additional requirement that
the color-terms and the zero-points to be the same for the two
nights. Second-order extinction terms were not included. The
calibrations for the two nights agree very well within the es-
timated photometric (statistical) errors. The weighted average
magnitudes from the calibration in the two nights and the corre-
sponding errors are given in Table 2. Note that the uncertainties
of the calibrated magnitudes are donated by the uncertainty of
the zero-point and not by the statistical uncertainty. A compari-
son between the stars in common with Leonard et al. (2005) and
Anupama et al. (2005) reveals that there are small systematic dif-
ferences between the photometry; ours being generally brighter.
The mean differences with the BVRI photometry of Leonard
et al. (2005) are, respectively, 0.010 ± 0.020, 0.013 ± 0.020,
0.039 ± 0.010 and 0.013 ± 0.027 mag. Excluding star #1 which
is brighter in Anupama et al. (2005) in all bands, the mean dif-
ferences are 0.00±0.05, 0.06±0.01, 0.04±0.01, 0.06±0.02 and
0.015 ± 0.010 mag for the UBVRI bands, respectively. Some of
these differences are non-negligible and we have no explanation
of why they appear in the comparison stars calibrations. This
is clearly worrisome and emphasizes one important source of
systematic errors when different SN data sets are combined and
used to derive cosmological parameters.
Landolt (1992) standard fields were observed to derive the
instrument color-terms (ct), allowing us to transform the pho-
tometry of SN 2003du to the standard Johnson-Cousins system.
The instrumental magnitudes of the standard stars were mea-
sured by aperture photometry with large apertures. All measure-
ments for a given instrument were fitted simultaneously (with
3σ clipping) with linear equations of the form:
U − u = ctU(U − B) + zp , B − b = ctB(B − V) + zp
V − v = ctV (B − V) + zp , R − r = ctR(V − R) + zp (1)
I − i = ctI(V − I) + zp
to determine the cts. The upper-case and lower-case letters de-
note the standard and instrumental magnitudes, respectively.
For each SN image, a zero-point was calculated for each
calibrated star by applying Eqs. 1. The final image ZP and its
uncertainty are, respectively, the average of the individual ZPs
2 Available at http://cadcwww.hia.nrc.ca/standards/ and as
discussed by Stetson (2000) this photometry is essentially in the Landolt
(1992) system.
(with 3σ outliers removed if present) and the standard deviation.
The measured scatter for the brightest stars was always larger
than expected from Poisson statistics. This indicates that there
are additional sources of uncertainties: imperfect flat-fielding,
presence of non-uniform scattered light, CCD non-linearity, etc.
Considering the magnitude scatter of the brightest stars we esti-
mate that these effects contribute ≤ 0.01 mag to the error budget.
Finally, the ZPs were added to the measured SN magnitudes to
obtain the magnitudes in the natural systems of the instruments
used, mnat.
The SN magnitudes can be transformed to a standard photo-
metric system using the color corrections obtained with Eqs. 1.
It is, however, well known that these color corrections do not
work well for SNe and significant systematic differences be-
tween photometry obtained with different instruments are of-
ten observed (Suntzeff, 2000; Stritzinger et al., 2002; Krisciunas
et al., 2003). The reason is that the SN spectral energy distribu-
tion (SED) is very different from that of normal stars. Another
consequence of this is that if a given band is calibrated against
different color indices, e.g. V(B − V) and V(V − R), one would
get the same magnitude for normal stars but slightly different
magnitudes for objects with non-stellar SEDs. This is because
the color-terms are determined with normal stars, but SNe oc-
cupy a different region in the color-color diagrams. The pho-
tometric observations of SN 2003du were collected with many
different instruments and we chose to standardize the photome-
try using the S-correction method described by Stritzinger et al.
(2002) coupled with our very well-sampled spectral sequence
of SN 2003du. The S-correction method assumes that the SED
of the SN and the response of the instruments used for the ob-
servations are both accurately known. Then one can correct the
photometry to any well-defined photometric system by means
of synthetic photometry. If f phot
(λ) is the photon flux of the ob-
ject per unit wavelength, mnat the object magnitude as defined
above, Rnat(λ) the response of the natural system and Rstd(λ) the
response of the standard system, then the object standard mag-
nitude mstd is:
mstd = mnat −2.5 log
(λ)Rstd(λ)dλ
+2.5 log
(λ)Rnat(λ)dλ
+const (2)
The constant in Eq. 2 is such that the correction is zero for A0 V
stars with all color indices zero. This ensures that for normal
stars the synthetic S-correction gives the same results as the lin-
ear color-term corrections (Eq. 1). The constant can be deter-
mined from synthetic photometry of stars for which both pho-
tometry and spectrophotometry is available. The details of the
application of the S-corrections are given in the Appendix. In
Fig. 2 we only show the time evolution of the difference between
the S-correction and the linear color-term correction. Note the
particularly large difference for Calar Alto I, and NOT R and
I-bands, as well as the rather large scatter for the V-band at all
epochs and for the B-band after +20 days.
The final photometry of SN 2003du is given in Table 3. Note
that none of the U-band and part of the BVRI photometry could
be S-corrected. Additional B and V photometry obtained at
Moscow and Crimean Observatories is given in Table 4. Figure 3
shows a comparison between the S-corrected and color-term cor-
rected B − V color index and I magnitudes. It is evident that
in the color-term corrected photometry small systematic differ-
ences between the various setups exist. It is also evident that
the S-correction removes those differences to a large extent, the
exception being the BAO data at early epochs. Significant im-
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 5
−0.06
−0.04
−0.02
B−band
Days from Bmax
Asiago
Calar Alto
−0.06
−0.04
−0.02
0.04 V−band
0 50 100
−0.04
−0.02
R−band
0 50 100
I−band
Fig. 2. Time evolution of the difference be-
tween the S-correction and the linear color-
term correction.
provement is also achieved for the I-band, which required the
largest S-corrections.
2.3. Near infrared photometry and spectroscopy
Near infrared JHK photometry of SN 2003du was obtained on
six nights at TNG and NOT. The two telescopes use identical J
and H filters, but the TNG uses a K′ while the NOT has a Ks
filter (Tokunaga et al., 2002). The observations were reduced in
the standard way, using the XDIMSUM package in IRAF.
The two nights at the NOT were photometric and standard
stars from the list of Hunt et al. (1998) were observed in or-
der to calibrate a local sequence of stars. However, only star
#3 (Fig. 1) could be reliably calibrated because it is the only
one that is faint enough to be in the linear range of the de-
tector and is bright enough to give an adequate S/N. The av-
erage NIR magnitudes of star #3 are J = 14.67, H = 14.38
and K = 14.37, all with uncertainties of ∼ 0.03 mag. The cali-
brated magnitudes are in good agreement with the 2MASS val-
ues, which are J = 14.633 ± 0.037, H = 14.362 ± 0.056 and
K = 14.311 ±0.062. Star #3 was used to calibrate the TNG pho-
tometry. No color terms were applied. The NIR photometry of
SN 2003du is given in Table 5.
Eleven low-resolution NIR spectra of SN 2003du were ob-
tained at UKIRT and TNG (Table 6). At UKIRT, the spectral
range was covered by using different instrument settings. At
TNG an AMICI prism was used as disperser. In this mode the
whole NIR spectral range is provided in one exposure at the ex-
pense of having very low resolving power (≤ 100). Both sets of
observations were performed in ABBA sequences, where A and
B denote two different positions along the slit. After bias/dark
and flat field corrections, for each pair of AB images, the B im-
age was subtracted from the A image. The negative spectrum
was shifted to the position of the positive one and subtracted
from it. This resulted in an image with the sum of the spectra
but minus the sky background. All such images were summed
into a single image and the 1D spectra were then optimally ex-
tracted. We note that the optimal extraction algorithm has to be
applied on images where the pixel levels are given in the form of
actual detected counts, and so it will not work quite correctly if
applied to background-subtracted images. Special care was thus
taken to calculate the optimal extraction weights correctly. The
Table 4. Additional photometry SN 2003du.
JD Phase B V Telescope
2452765.38 −1.0 13.45 (0.01) 13.61 (0.01) 1
2452768.33 +2.0 13.49 (0.02) 13.57 (0.02) 1
2452775.38 +9.0 13.95 (0.01) 13.83 (0.01) 1
2452782.37 +16.0 14.65 (0.05) 14.17 (0.02) 2
2452786.33 +20.0 14.99 (0.06) 14.43 (0.02) 2
2452792.31 +25.9 · · · 14.73 (0.06) 3
1 – 70-cm Moscow reflector + CCD Pictor 416; 2 – 30-cm Moscow
refractor + CCD AP-7p; 3 – 38-cm Crimean reflector + CCD ST-7;
UKIRT spectra were wavelength calibrated with arc-lamp spec-
tra, while for the TNG spectra a tabulated dispersion solution
relating pixel number to wavelength was used. The dispersion of
the UKIRT spectra ranges from ∼ 5 Å pixel−1 to ∼ 25 Å pixel−1,
while for the TNG spectra, the dispersion is in the ∼ 30 Å pixel−1
– ∼ 100 Å pixel−1 range.
The A5 V star AS-24 (Hunt et al., 1998) and the F7 V star
BS5581 (from the list of UKIRT standard stars) were observed
at TNG and UKIRT respectively. The standard stars were ob-
served close in time and airmass to the SN observations. The SN
spectra were first divided by the spectra of the comparison stars
to remove the strong telluric absorption features. The result was
multiplied by a model spectrum of the appropriate spectral type,
smoothed to the instrumental resolution, to remove any residual
features due to the absorption lines of the standard, simultane-
ously providing the relative flux calibration. The UKIRT spec-
tra from the different instrument settings that did not overlap
were combined using the SN 2003du photometry and average
NIR color indices of normal SNe Ia.
3. Results
3.1. Light curves
The UBVRIJHK light curves (LCs) of SN 2003du are shown
in Fig. 4. The light curves morphology resemble that of a nor-
mal SN Ia with a well-pronounced secondary maximum in the
I-band and a shoulder in the R-band. The J-band also shows
a strong rise towards a secondary maximum. Comparison with
the photometry of Leonard et al. (2005) and Anupama et al.
6 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
−15 −10 −5 0 5 10
Asiago
Calar Alto
S−corrected
a) color−termcorrected + 0.1
40 50 60 70 80 90
S−corrected
color−term
corrected + 0.1
−10 0 10 20 30 40
Days from Bmax
   NOT    Asiago   Calar Alto
   NOT    BAO
   S−corrected
Fig. 3. Comparison between the S-corrected and color-term corrected a-
b B − V color index and c I-band magnitude. The color-term corrected
B − V data are shifted by 0.1 mag. A polynomial fit to the S-corrected
B − V data is overplotted. To highlight the differences the fit is also
plotted shifted by 0.1 mag.
Table 5. NIR photometry of SN 2003du. The observations on 10.5 and
11.5 days are from NOT. The other four are from TNG.
JD Phase J H K
[day]
2452755.41 −11.5 14.96 (0.04) 15.02 (0.04) 15.02 (0.04)
2452768.68 +1.7 14.42 (0.04) 14.66 (0.04) 14.38 (0.04)
2452773.43 +6.5 14.92 (0.04) 14.77 (0.04) 14.53 (0.04)
2452777.46 +10.5 15.67 (0.04) 14.86 (0.04) 14.70 (0.04)
2452778.51 +11.5 15.84 (0.04) 14.86 (0.04) 14.75 (0.04)
2452782.58 +15.6 16.12 (0.04) 14.85 (0.04) 14.65 (0.04)
(2005) reveals fairly good consistency. However, systematic dif-
ferences between the data sets do exist and our photometry is
generally brighter. This is probably due to the differences in the
comparison star calibrations, as well as to the fact that our pho-
tometry was S-corrected, unlike those of Leonard et al. (2005)
and Anupama et al. (2005). To estimate the differences we fit-
ted a smoothing spline function to our data and computed the
mean difference and its standard deviation from Leonard et al.
(2005) and Anupama et al. (2005) photometry. The difference
slightly varies with the SN phase. Up to 30 days after maximum
light the mean differences and standard deviations in BVRI are,
respectively, 0.068 ± 0.030, 0.046 ± 0.029, 0.047 ± 0.022 and
Table 6. Log of the NIR spectroscopy
Date (UT) JD Phase Coverage Telescopea
[day] [µm]
2003 Apr 25 2452754.89 −11.5 0.8-2.5 UK-1
2003 Apr 25 2452755.47 −10.9 0.75-2.45 TNG
2003 May 01 2452760.89 −5.5 0.8-2.5 UK-1
2003 May 04 2452763.88 −2.5 1.42-2.4 UK-2
2003 May 08 2452768.68 +2.3 0.9-2.3 TNG
2003 May 10 2452769.79 +3.4 1.39-2.50 UK-2
2003 May 11 2452770.90 +4.5 0.8-2.5 UK-1
2003 May 19 2452778.80 +12.4 1.48-2.30 UK-2
2003 May 22 2452782.58 +16.2 0.9-2.48 TNG
2003 May 27 2452786.77 +20.4 0.8-2.5 UK-1,2
2003 Jun 06 2452796.80 +30.4 0.8-2.5 UK-1,2
aTNG = TNG + NICS, UK-1/2 = UKIRT + CGS4/UIST
0.042±0.037 mag with Anupama et al. (2005) and 0.026±0.025,
0.026±0.015, 0.014±0.015 and 0.071±0.030 mag with Leonard
et al. (2005). The difference with the Anupama et al. (2005) U-
band photometry is 0.007 ± 0.085 mag.
We fitted the B-band template of Nugent et al. (2002) to the
data to determine the B-band light curve parameters. This pro-
vided the time of B maximum light tBmax (JD)=2452766.38 (2003
May 6.88 UT), stretch factor sB = 0.988±0.003 and peak magni-
tude Bmax = 13.49 ± 0.02 mag. The peak VRI magnitudes were
estimated by fitting low-order polynomials to the data around
maximum, giving Vmax = 13.57± 0.02, Rmax = 13.57± 0.02 and
Imax = 13.83 ± 0.02 mag. The U-band maximum was estimated
by fitting our own template derived from the SNe published by
Jha et al. (2006a): Umax = 13.00 ± 0.05 mag. The optical pho-
tometric coverage around 15 days after Bmax is rather sparse.
However, the B-band template matches the observed photome-
try very well, thus we are able to use this to determine the decline
rate parameter. We find ∆m15 = 1.02±0.05. BVRI template light
curves with ∆m15 = 1.02 were also generated using the data and
the method described by Prieto et al. (2006). These light curves
are also shown in Fig. 4, shifted to match SN 2003du peak mag-
nitudes. The resemblance between SN 2003du light curves and
the templates is excellent.
The NIR templates from Krisciunas et al. (2004b) were fitted
to the first three JHK photometric points (Fig. 4) to estimate the
peak magnitudes: Jmax = 14.21, Hmax = 14.56 and Kmax = 14.29
mag. The rms around the fits are fairly small 0.03, 0.02 and 0.04
mag, respectively, but because the LCs are undersampled the un-
certainties in the peak magnitudes should exceed these values.
To derive the templates, Krisciunas et al. (2004b) fitted third-
order polynomials to the photometry of a number of SNe. The
rms around the fits are 0.062, 0.080 and 0.075 mag for J, H and
K, respectively. These numbers were added in quadrature to the
rms around the fits to the SN 2003du data to obtain the uncer-
tainties of the JHK peak magnitudes, 0.07, 0.08 and 0.09 mag,
respectively.
The entire light curves are shown in the inset of Fig. 4. The
late-time HS T data from Leonard et al. (2005) are also shown
(open symbols); these are consistent with our ground based pho-
tometry. After ∼ +180 days the magnitudes of SN 2003du de-
cline linearly, following the expected form of an exponential ra-
dioactive decay chain. The decline rates in magnitudes per 100
days in UBVRI-bands (as determined by linear least-squares fit-
ting) are 1.62 ± 0.12, 1.47 ± 0.02, 1.46 ± 0.02, 1.70 ± 0.06 and
1.00 ±0.03, respectively. The decline rates in the B- and V-bands
are virtually the same. The I-band decline on the other hand is
much slower than in the other bands. Many other normal SNe Ia
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 7
0 50 100 150
Days from Bmax
0 50 100 150 200 250 300 350 400 450 500
Days after Bmax
Fig. 4. UBVRIJHK light curves of SN 2003du. The error bars are not plotted because they are typically smaller than the plot symbols. For the
BVRI bands the filled and the open symbols are the S-corrected and non-S-corrected photometry, respectively. The open symbols for J band are
synthetic photometry from the combined optical-NIR spectra. Overplotted are the B-band template of Nugent et al. (2002), the JHK templates
from Krisciunas et al. (2004b) (solid lines), as well as our U-band template derived from Jha et al. (2006a) data (dashed line). The dotted lines are
a light curve template with ∆m15 = 1.02 calculated as described in Prieto et al. (2006) using a program provided by the authors. Inset: The full
light curves. The late-time HS T data from Leonard et al. (2005) are also shown with the open symbols. The linear fits to the late-time photometry
are also shown.
(e.g., Lair et al., 2006) and the peculiar SN 2000cx (Sollerman
et al., 2004) also show similar behavior.
3.2. Reddening in the host galaxy
Figure 5 shows that the time evolution of the color indices (CIs)
of SN 2003du closely follows the reddening corrected CIs of
normal SNe such as 1990N, 1998aq, and 1998bu, as well as the
Nobili et al. (2003) templates. This implies that SN 2003du was
probably not reddened within its host galaxy. Nevertheless, the
reddening in the host galaxy was estimated with three different
methods. The CIs of SN 2003du were first corrected for the small
Milky Way reddening of E(B−V) = 0.01 (Schlegel et al., 1998)
assuming RV = 3.1.
i) Phillips et al. (1999) use the observed Bmax − Vmax and
Vmax−Imax indices, and the evolution of B−V between 30 and 90
days after maximum to derive E(B− V). The first two quantities
are weak functions of ∆m15. The time evolution of B−V (known
as the Lira relation) seems to hold for the majority of SNe Ia
(Phillips et al., 1999; Jha et al., 2006b). Following Phillips et al.
(1999), for SN 2003du we obtain E(B − V)max = −0.01 ± 0.04,
E(V − I)max = 0.07 ± 0.05 and E(B − V)tail = 0.05 ± 0.07.
8 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
Lira−Phillips relation
2003du
1990N
1998bu
1998aq
Nobili et al. (2003)
−20 0 20 40 60 80 100
Days from Bmax
−20 0 20 40 60 80 100
Days from Bmax
Fig. 5. The evolution of the optical color indices of SN 2003du, compared with those of other well-observed SNe Ia. When necessary the colors
were de-reddened with the appropriate E(B − V). The Nobili et al. (2003) B − V , V − R and V − I templates are also shown.
The errors indicate the intrinsic accuracy of the three methods as
given in Phillips et al. (1999), viz. 0.03, 0.04 and 0.05, added in
quadrature to the uncertainties of the observed CIs. Note that the
B − V evolution of SN 2003du has a different slope from that of
the Lira relation, leading to rather a large scatter of ∼ 0.07 mag.
We averaged the above estimates of E(B − V)max, 0.8×E(V −
I)max
3 and E(B−V)tail weighted by their respective uncertainties
to obtain the final reddening estimate: E(B−V) = 0.027 ±0.026.
ii) Wang et al. (2003b) introduced a novel method,
CMAGIC, to estimate the brightness and the reddening of
SNe Ia. It is based on the observation that between 5-10 to 30-
35 days after maximum the B magnitude is a linear function of
B − V with a fairly uniform slope. Applying this method, we
obtain E(B − V) = 0.00 ± 0.05.
iii) Krisciunas et al. (2000, 2001, 2004b) have shown that
the intrinsic V − (JHK) CIs of SNe Ia are very uniform and can
be used to estimate the reddening of the host galaxy. Figure 6
shows the V − (JHK) CIs of SN 2003du overplotted with the
unreddened loci for mid- (∆m15 = 1.0 − 1.3) and slow-declining
SNe (∆m15 = 0.8− 1.0) of Krisciunas et al. (2004b). Most of the
V − (HK) data of SN 2003du fall between the two loci. This is
consistent with the fact that its ∆m15 = 1.02 lies between these
two groups of SNe Ia. Although the V − J CI is slightly redder
than the locus, overall the V − (JHK) CIs of SN 2003du suggest
little reddening.
Combining the results of the three estimates we conclude
that SN 2003du suffered negligible reddening within the host
galaxy. The main parameters of SN 2003du that we derived from
photometry are summarized in Table 7.
3 the factor 0.8 serves to convert E(V − I) to E(B − V) assuming the
standard Milky Way extinction law with RV = 3.1.
slow-decliners (∆m15=0.8-1.0)
mid-decliners  (∆m15=1.0-1.3)
-10 0 10 20 30
Days from Bmax
Fig. 6. V − (JHK) color indices of SN 2003du. The unreddened loci
for mid- and slow-declining SNe of Krisciunas et al. (2004b) are over-
plotted. The open symbols are estimates based on synthetic photometry
from the combined optical-NIR spectra.
3.3. Spectroscopy
Our collection of optical spectra of SN 2003du is shown in
Figs. 7 and 8. The spectra marked with an asterisk have been
smoothed using the á trous wavelet transform (Holschneider
et al., 1989). The optical spectral evolution of SN 2003du is
that of a normal SN Ia. In the earliest spectrum at −13 days the
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 9
4000 6000 8000 10000
Rest frame wavelength [Å]
−12.8 *
−10.9
−10.8
−7.8 *
+10.0
+15.1
+17.2
+18.2
+19.0
+21.1
+26.1
+31.2 +34.1
+39.0
+45.2
+51.1
+63.1
+72.0
+84.0
+108.9
+141.4
high−velocity Ca II
HV Ca II
Fig. 7. Evolution of the optical spectra of SN 2003du. The spectra marked with an asterisk were slightly smoothed (see text for details). The
noticeable telluric features are marked with Earth symbols; the connected symbols mark the region of strong telluric absorption.
Si ii λ6355 line is strong and broad (∼ 10000 km s−1 full-width
at half-depth), and the S ii λ5454 and λ5640 lines are well devel-
oped. In the −11 day spectrum the Ca ii H&K and the IR triplet
lines are also very strong. In all the spectra until one week after
maximum light, Si ii λ4129 and λ5972 lines are clearly visible.
Mg ii λ4481, Si iii λλ4553,4568 and the blend of Fe ii, Si ii and
S ii lines around 4500–5000 Å are also prominent. A few days
after Bmax the spectrum starts to be dominated by Fe group ele-
ments and gradually evolves into a nebular spectrum.
The ratio between the depth of the Si ii λ5972 and λ6355
lines, R(Si ii) (Nugent et al., 1995), at maximum is R(Si ii) =
0.22 ± 0.02, typical for normal SN Ia. R(Si ii) does not change
significantly in the pre-maximum spectra, remaining at ∼ 0.2.
In Fig. 9 three of the pre-maximum spectra of SN 2003du are
compared with spectra of other normal SNe Ia observed at sim-
ilar epochs and appropriately de-reddened. For this and other
comparison plots we use published optical spectra of SN 1994D
(Patat et al., 1996; Filippenko, 1997; Meikle et al., 1996),
SN 1990N (Leibundgut et al., 1991), SN 1996X (Salvo et al.,
2001), SN 1999ee (Hamuy et al., 2002), SN 1998aq (Branch
et al., 2003), SN 1998bu (Jha et al., 1999; Hernandez et al.,
2000), SN 2002er (Kotak et al., 2005), SN 2001el (Wang et al.,
10 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
Table 7. Main photometric parameters of SN 2003du from this work.
tBmax [JD] 2452766.38 ± 0.50
tBmax (UT date) May 6.88, 2003
B-band stretch, sB 0.988±0.003
B-band decline rate, ∆m15 1.02±0.05
Peak magnitudes U = 13.00 ± 0.05 B = 13.49 ± 0.02
V = 13.57 ± 0.02 R = 13.57 ± 0.02
I = 13.83 ± 0.02 J = 14.21 ± 0.07
H = 14.56 ± 0.08 K = 14.29 ± 0.09
Late-time decline γU = 1.62 ± 0.12 γB = 1.47 ± 0.02
rate γ [mag/100 days] γV = 1.46 ± 0.02 γR = 1.70 ± 0.06
γI = 1.00 ± 0.03 γBol = 1.40 ± 0.01
E(B − V)host 0.00±0.05
4000 5000 6000 7000 8000
Rest frame wavelength [Å]
+195.9 *
+195.9
+209.3 *
+221.3
+272.3 *
+376.9
SN 1998bu
Fig. 8. Nebular spectra of SN 2003du. The spectra marked with an aster-
isk were slightly smoothed. A nebular spectrum of SN 1998bu is shown
for comparison.
2003a; Mattila et al., 2005) and SN 2005cg (Quimby et al.,
2006). The spectra at about 10 days before maximum show sig-
nificant differences. The spectra have not been taken at exactly
the same phase and the rapid spectral evolution at such early
phases may partly be responsible for the differences. However,
most of the differences are most likely intrinsic. It worths noting
that the weak feature at ∼6300 Å that is visible in the two earliest
spectra of SN 2003du is present in other SNe Ia as well (Fig. 10)
and has been attributed to C ii λ5860 (Mazzali, 2001; Branch
et al., 2003; Garavini et al., 2004, 2005). At one week before
maximum the spectra are more similar to each other. It is inter-
esting to note that at these epochs the largest differences between
the SNe are seen in the strengths and profiles of the Si ii λ6355,
Ca ii H&K and Ca ii IR3 lines. Starting from one week before
maximum the spectra of most SNe Ia are very homogeneous.
The NIR spectra of SN 2003du are shown in Fig. 11. The
earliest spectra at −11.5 and −11 days are rather featureless with
only hints at weak broad P-Cygni profiles. The weak ∼ 1.05µm
absorption could be due to Mg ii λ10926 or He i λ10830 (or a
combination of the two) (Meikle et al., 1996; Mazzali & Lucy,
1998; Branch et al., 2004; Marion et al., 2003). The strength
of this absorption in the earliest two spectra is quite different,
despite the fact that they have been taken only half a day apart.
In the −11.5 days spectrum, however, the absorption is likely
99ee −9d
90N  −14d
03du −12.8d
03du −10.9d
01el −9d
98aq −9d
02er −11d
94D −12d
Early spectra (day −11)
Ca II H&K
Ca II IR3
Si II
4000 6000 8000 10000
Rest frame wavelength [Å]
99ee −7d
90N  −7d
03du −5.8d
98bu −6.5d
98aq −8d
02er −6.3d
94D −7.5d
one week before maximum
Fig. 9. Comparison of optical spectra of normal SNe Ia at two pre-
maximum epochs. The arrows in the lower panel mark the lines whose
velocities have been measured.
enhanced by a noise spike due to the low instrument response at
this wavelength.
In the day −5.5 spectrum an absorption due to Mg ii λ9226
(Marion et al., 2003) is clearly seen. In the earlier IR spec-
tra there are only hints of its presence and it may be just de-
tectable in the optical spectrum at day −11. Our experiments
with the SN spectral synthesis code SYNOW (see for details,
e.g. Branch et al., 2003) show however, that Si iii and possibly
Si ii may contribute to the red part of this line. No other fea-
tures are detected in the 0.9-1.2µm spectral region. In particular,
no C i or O i lines are observed, in accordance with the findings
of Marion et al. (2006). The absorption at ∼ 1.21µm is due to
Ca ii according to Wheeler et al. (1998), but the associated emis-
sion peak at ∼ 1.24 µm was attributed to Fe iii by Rudy et al.
(2002) in SN 2000cx. The 1.6µm absorption seen in the spectra
until maximum light is due to Si ii with a possible contribution
from Mg ii (Wheeler et al., 1998; Marion et al., 2003). The broad
features beyond ∼ 1.7µm lack clear identification. Possible con-
tributors are Si iii at ∼ 2 µm (Wheeler et al., 1998) and Co ii at
∼ 2 − 2.05µm and ∼ 2.3 µm (Marion et al., 2003).
By day +12, two strong emission features at ∼ 1.55µm and
∼ 1.75µm dominate the 1.4-1.8µm spectral region. These two
features are formed by blending of many Fe ii, Co ii and Ni ii
emission lines (Wheeler et al., 1998). Lines of Fe ii, Co ii, Ni ii
and Si ii dominate the spectral region beyond 2 µm. From day
+15, a number of lines, with uncertain identifications also de-
velop in the J band. One can also clearly see how a flux deficit
at ∼ 1.35µm develops. This causes the very deep minimum ob-
served in the J-band light curves of most SNe Ia around 20 days
after maximum.
Figure 12 presents a comparison of several IR spectra of
SN 2003du with those of other normal SNe: SN 1994D (Meikle
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 11
5600 6000 6400
Rest frame wavelength [Å]
03du −12.8
03du −10.9
99ac −15
98aq −9
96X −4
94D −10
90N −14
C II 6580?
Fig. 10. Early spectra of SN 2003du and several other SNe Ia zoomed at
the Si ii 6355 line. The dotted lines mark the weak absorption features
that may be due to C ii λ6580.
et al., 1996), SN 1999ee (Hamuy et al., 2002), SN 1998bu (Jha
et al., 1999; Hernandez et al., 2000; Hamuy et al., 2002), and
SN 2002bo (Benetti et al., 2004). Similarly to the optical, the IR
spectra of normal SNe taken at similar epochs are very homoge-
neous, even the spectra taken 6–12 days before maximum. The
only significant difference is in the J-band, where the Mg ii lines
of SN 2002bo are stronger compared to other SNe.
3.4. Blueshifts of absorption-line minima
We have measured the blueshifts of the absorption-line min-
ima of Si ii λ6355, S ii λ5640 and Si iii λλ4553,4568, which are
thought to be relatively un-blended (Branch et al., 2003), by fit-
ting a Gaussian to the line absorption troughs. In the rest of
the paper we report the velocities that correspond to the mea-
sured blueshifts of the absorption-line minima (unless otherwise
stated) and will refer to these as velocities of the absorption lines.
By convention, these velocities are negative and we say that the
velocity of a line increases from, e.g. −20000 to −10000 km s−1.
The velocities inferred from an explosion model will be reported
as positive numbers.
The velocities of the Si ii λ6355, S ii λ5640 and
Si iii λλ4553,4568 lines are shown in Fig. 13 and it is evi-
dent that the time evolution is very similar to that in other
normal SNe Ia (see, e.g. Benetti et al., 2005). The Si ii λ6355
velocity initially increases rapidly, but 7–5 days before max-
imum the increase rate slows down and the velocity remains
almost constant thereafter. The velocities of the S ii λ5640
and Si iii λλ4553,4568 lines increase at nearly constant rate;
however, there is a hint that the S ii λ5640 velocity remains
constant after maximum, similarly to Si ii λ6355. Benetti et al.
(2005) measured a post-maximum velocity increase rate of
the Si ii λ6355 line to be v̇ = 31 ± 5 km s−1d−1 and classified
SN 2003du as a Low Velocity Gradient SN Ia, along with
other normal and all overluminous SNe Ia. It can be seen
from Fig. 1 in (Benetti et al., 2005) that before maximum the
Si ii λ6355 velocities of SN 2003du are systematically higher by
500-2000 km s−1 compared to all other SNe.
During the SN photospheric epochs the main source of
continuum opacity at the optical wavelengths is electron scat-
tering and following Jeffery et al. (1992) we adopt that the
1.0 1.5 2.0 2.5
Rest frame wavelength [µm]
 −11.5
 −10.9
  −5.5
  −2.5*
  +2.3
  +3.4*
  +4.5
 +12.4*
 +16.2
 +20.4
 +30.4
Mg II + He I?
Mg II
Si II/Mg II?
Ca II
Ca II
Fe III?
Si III?
Co II?
Co II?
Ca II
Fe/Si edge
Fe/Ni/Co
Fe II
Fe/Ni/Co/Si
Fe/Ni/Co/Si?
Fig. 11. NIR spectral evolution of SN 2003du. The spectra marked with
an asterisk have been smoothed (only the J band of the −2.5 days spec-
trum is smoothed).
(continuum) photosphere is at electron scattering optical depth
2/3. However, the velocity gradient in the expanding SN ejecta
causes many weak lines to overlap which gives rise to strong
pseudo-continuum (e.g., Pauldrach et al., 1996), and the so-
called expansion opacity (Karp et al., 1977; Pinto & Eastman,
2000) is an analytical description of this effect. This expan-
sion opacity may exceed electron scattering opacity by orders
of magnitude. The velocity of the pseudo-photosphere thus cre-
ated is wavelength-dependent. Besides, strong absorption lines
may form in a large volume above the continuum photosphere.
For these reasons, the line velocities we measure most likely do
not trace the velocity of the continuum photosphere and should
be interpreted with caution. Lentz et al. (2000) have computed
a grid of photospheric phase atmospheres of SNe Ia with differ-
ent metallicities in the C+O layer and computed non-LTE syn-
thetic spectra. It would be more reasonable for us to compare the
Si ii λ6355 line velocities in SN 2003du with the measurements
from the Lentz et al. (2000) synthetic spectra. The time evolution
is qualitatively similar and in Fig. 13 we also show the measure-
ments for the 1/3 Solar metallicity models, which best follows
the SN 2003du Si ii λ6355 line blueshift.
12 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
1.0 1.5 2.0 2.5
Rest frame wavelength [µm]
03du −11.5
99ee −9
02bo −9.2
94D −8.5
03du −5.5
03du −2.5
98bu −3
03du +2.3
99ee +2
03du +4.5
99ee +5
03du +16.2
98bu +15
Fig. 12. Comparison with NIR spectra of other normal SNe Ia.
Marion et al. (2003) showed that the velocities of lines in
NIR spectra could be used to constrain the location of the tran-
sition region between the layers of explosive carbon and oxygen
burning, and incomplete to complete silicon burning, and hence
place constraints on the explosion models. We measured the ve-
locities of the blue edges of the absorptions at ∼ 0.9 µm and
1.05µm in our optical and IR spectra between −11.5 and +4.5
days. Both lines show constant velocities of ∼ −11000 km s−1
and ∼ −13000 km s−1, respectively, assuming that the lines are
formed by Mg ii λ9226 and Mg ii λ10926. The constant veloc-
ity indicates that the continuum photosphere is well beneath the
Mg-rich layers (Meikle et al., 1996). The velocity of the sharp
edge at ∼ 1.55 µm in the spectra between +10 and +20 days
can be used to estimate the transition between the layers of
incomplete and complete silicon burning. We measure veloci-
ties ≤ −9800 km s−1 which is similar to the results of Marion
et al. (2003) and is also broadly consistent with their refer-
ence explosion model in which Si is completely consumed be-
low ∼ 8500 km s−1. This ties in with the measurements of the
Si ii λ6355 line velocity, which is always ≤ −9300 km s−1.
4. Discussion
4.1. The distance to SN 2003du
We have shown that SN 2003du was a spectroscopically and
photometrically normal SN Ia, and furthermore that it was not
reddened within its host galaxy. The distance to UGC 9391 has
not been measured using direct techniques, and the only avail-
−10 0 10 20 30 40
Days from Bmax
− Si II λ6355
− Si III λ4560
− S II λ5640
Lentz model
1/3 Solar metallicity
Fig. 13. The evolution of the velocity of the absorption lines of
SN 2003du.
able information is from its recession velocity. The observed
velocity is 1914 km s−1, which after correcting for the Local
Group in-fall onto Virgo becomes 2195 km s−1 (from the LEDA
database) or a distance modulus of µ = 32.42 mag on the scale
of H0 = 72 km s
−1,Mpc−1.
Recently, Riess et al. (2005) calibrated the luminosities of
SN 1998aq and SN 1994ae by observing Cepheids in their host
galaxies with the Hubble Space Telescope. Including two other
SNe Ia with Cepheid calibrated distances, they estimated the
absolute magnitude of a typical SN Ia to be MV = −19.20
±0.10(statistical)±0.115(systematic) mag. Meikle (2000) and
Krisciunas et al. (2004a,c) presented evidence that SNe Ia are
standard candles in the NIR and that no correction for the light
curve shape is needed for SNe with ∆m15 < 1.7 mag. Krisciunas
et al. (2004c) derived the following absolute peak JHK mag-
nitudes for H0 = 72 km s
−1,Mpc−1: −18.61,−18.28 and −18.44
mag all with statistical uncertainty of ∼ 0.03 mag. The system-
atic uncertainty of MV is mostly due to the 0.1 mag uncertainty in
the distance to the Large Magellanic Cloud (LMC) and hence it
also affects the NIR absolute magnitudes and the distance mod-
ulus derived from the host galaxy recession velocity (through
H0). The light curve decline rate parameter ∆m15 = 1.02 ± 0.05
and the normal spectral evolution suggest that SN 2003du is very
similar to normal SNe Ia. If one assumes that SN 2003du had the
above-mentioned absolute VJHK magnitudes, a distance mod-
ulus of µ = 32.79 ± 0.04 (or a radial velocity of ∼ 2600 km s−1
with H0 = 72 km s
−1,Mpc−1) is obtained 5. This estimate is the
average of the four individual estimates weighted by their sta-
tistical uncertainties, i.e. the errors of SN 2003du peak VJHK
magnitudes added in quadrature to the statistical uncertainties of
the absolute magnitudes.
The difference between the two distance moduli is 0.37 mag
(it will further increase if the Meikle 2000 absolute NIR mag-
nitudes are used) and indicates that SN 2003du was fainter than
the average of SNe with ∆m15 = 1.02. The 1σ dispersion of
SNe Ia absolute magnitudes in both, optical and IR, is ∼ 0.15
mag (e.g., Phillips et al., 1999; Krisciunas et al., 2004c). The
4 Riess et al. (2005) estimated H0 = 73 km s
−1,Mpc−1 and
MV = −19.17, and we converted their MV to the scale of H0 =
72 km s−1,Mpc−1
5 The absolute JHK magnitudes of Meikle (2000) are by 0.4 mag
brighter than those of Krisciunas et al. (2004c). The distance moduli
derived with the values from the latter paper are consistent with the
estimates of absolute V magnitude from Riess et al. (2005); we therefore
adopt the Krisciunas et al. (2004c) values.
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 13
uniformity and the small dispersion of the V − [JHK] colors
of SNe Ia (Krisciunas et al., 2004b) indicates that the intrinsic
scatter in the VJHK bands is correlated, and so cannot be re-
duced by averaging observations in different bands. Therefore,
the distance modulus we estimate, µ = 32.79 ± 0.04 mag, has
an additional ∼ 0.15 mag uncertainty from the intrinsic disper-
sion of SNe Ia luminosity. The fact that SN 2003du is 0.37 mag
fainter than expected for SNe with ∆m15 ∼ 1.02 may thus be
due to the intrinsic scatter (2.5σ from of the mean). It is also
possible that UGC 9391 may not be in the undisturbed Hubble
flow: if it has vr = 2600 km s
−1 and a peculiar velocity compo-
nent of ∼ 400 km s−1 toward the Earth, it may seem closer than
it really is. UGC 9391 is nearly face-on and the contribution of
the galaxy rotation should be small.
4.2. The bolometric light curve
In order to compute the uvoir ”bolometric” light curve (i.e. the
flux within the 0.2-2.4µm interval) of SN 2003du we proceeded
as follows. First, our U-band template LC was fitted to the U
photometry in order to estimate the U magnitudes when only
BVRI were available. The magnitudes were corrected for the
small Galactic reddening and transformed to flux densities us-
ing the absolute calibration of the UBVRI system by Bessell
et al. (1998). A cubic spline was fitted through the data points
and the resulting fit was integrated numerically over the interval
3500-9000 Å.
Most of the early-time SN Ia luminosity is emitted at optical
wavelengths, however, a non-negligible correction for the flux
emitted outside the optical wavelengths is also needed (see, e.g.
Suntzeff, 1996). The flux emitted beyond 9000 Å was estimated
by integrating the combined optical-NIR spectra of SN 2003du.
The filled circles in Fig. 14a show the time evolution of the ra-
tio of the flux emitted in the 9000-24000Å range to that emit-
ted within 3500-9000 Å. Suntzeff (1996) finds that at +80 days
less than 10% of the flux is emitted in the IR. We estimate from
the photometry of SN 2001el (Krisciunas et al., 2003) that the
contribution of the IR flux is ∼ 25% and ∼ 15% at +28 and
+64 days, respectively. This is consistent with our estimates for
SN 2003du and the findings of Suntzeff (1996), and indicates
that the contribution of the IR flux decreases roughly linearly
between days +30 and +80.
As there are no UV spectra of SN 2003du observed, we used
UV spectra of other SNe Ia to estimate the contribution of the
UV flux. These comprised combined de-reddened UV-optical
spectra of SN 1990N at −14 and −7 days (Leibundgut et al.,
1991), SN 1989B at −5 (Wells et al. 1994 and UV spectra from
the IUE archive), SN 1981B (Branch et al., 1983), SN 1992A
at +5, +9 and +17 (Kirshner et al., 1993), and SN 2001el be-
tween +30 and +66 (from HS T archive). For spectra that did
not cover the full 2000–9000 Å range we extrapolated to 9000 Å
using spectra of SN 2003du. The spectra of SN 2001el were lin-
early extrapolated from ∼ 2900 Å down to 2000 Å assuming that
the flux approached zero at 1000 Å. In Fig. 14a we show the ra-
tios of the fluxes in the 2000–3500Å range to those in the 3500–
9000 Å range (open symbols).
The total contribution of the UV and IR fluxes is plotted as
a dashed line in Fig. 14a, and one can see the particularly large
corrections needed before the B-band maximum and around the
secondary I-band maximum. Beyond +80 days we assumed a
constant IR contribution of 10% and that the UV contribution
decreases linearly from 5% at +80 days to zero at +500 days.
This correction was applied to the optical fluxes to derive the
uvoir fluxes of SN 2003du. These were converted to luminos-
ity assuming a distance modulus µ = 32.79 mag. The uvoir
”bolometric” light curve of SN 2003du is shown in Fig. 14b.
For comparison, we also show the bolometric light curve of
SN 2005cf (Pastorello et al., 2007b), which is very similar to
that of SN 2003du. The maximum uvoir ”bolometric” luminos-
ity of SN 2003du is 1.35(±0.20) × 1043 erg s−1 at ∼ 2 days
before the B-band maximum. Using Arnett’s Rule as formu-
lated by Stritzinger & Leibundgut (2005, their Eq. 7)) we es-
timate the amount of 56Ni synthesized during the explosion,
M56Ni = 0.68 ±0.14 M⊙. The error is a simple propagation of the
uncertainty of the bolometric peak luminosity and the relation
of Stritzinger & Leibundgut (2005). However, Khokhlov et al.
(1993) have shown that the simplifying assumptions made in the
derivation of Arnett’s rule may lead to errors as large as 50%.
Combined with the uncertainty of the distance to SN 2003du,
clearly this estimation of the 56Ni mass is subject to large sys-
tematic uncertainty. Note, however, that Stritzinger et al. (2006)
have analyzed a nebular spectrum and the optical photometry
of SN 2003du, and derived M56Ni ≃ 0.6 M⊙, which is in good
agreement with our estimate. If one accepts a distance modulus
of µ = 32.42 mag (∼ 30.4 Mpc), then the estimated peak lumi-
nosity and M56Ni should be reduced by ∼ 30%.
4.3. Bolometric light curve modeling
To further estimate the amount of 56Ni synthesized we mod-
eled the bolometric light curve of SN 2003du for both distance
moduli µ = 32.42 and µ = 32.79 mag. We used the Monte
Carlo light curve code described by Cappellaro et al. (1997) and
Mazzali et al. (2001). Starting from an explosion model and a
given 56Ni content the code computes the transport and deposi-
tion of the γ-rays and the positrons generated by the decay chain
56Ni→56Co→56Fe in a grey atmosphere. The optical photons
that are generated by the thermalization of the energy carried by
the γ-rays and the positrons are then followed as they propagate
through the SN ejecta. The optical opacity encountered by these
photons is again assumed to be grey and to depend primarily
on the relative abundance of iron-group elements. The opacity
also decreases with time as (td/17)
−3/2, td being the time since
the explosion in days, to mimic the effect of the decreasing tem-
perature. For more details on the adopted parametrization of the
opacity see, e.g. Mazzali et al. (2001). This simple approxima-
tion works well (e.g. Mazzali et al., 2001) but an alternative view
that the opacity depends primarily on temperature has been sug-
gested (Kasen & Woosley, 2007). In Mazzali et al. (2000) the
Monte Carlo code was compared with the results from the radia-
tion hydrodynamics code of Iwamoto et al. (2000), finding very
good agreement.
We followed the approach of Mazzali & Podsiadlowski
(2006), who assumed that stable Fe-group isotopes (e.g. 54Fe,
58Ni) may be present not only in the innermost part of the ejecta
(≤ 0.2 M⊙), but also in the
56Ni zone between ∼ 0.2 M⊙ and
∼ 0.8 M⊙. Mazzali & Podsiadlowski (2006) suggested that the
scatter of SNe Ia luminosity at a given ∆m15 may be reproduced
by changing the ratio of the amount of radioactive 56Ni and the
stable isotopes in the 56Ni zone, while keeping the total mass
of the Fe-group elements constant. This ratio may be sensitive,
for example, to the metallicity of the progenitor white dwarf
(Timmes et al., 2003). The SN Ia light curve width is mainly
determined by the opacity of the ejecta, which in turn is mostly
determined by the total amount (stable and radioactive) of Fe-
group elements synthesized, provided the temperature is above
∼ 104 K (e.g. Khokhlov et al., 1993). The peak luminosity on the
14 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
−20 0 20 40 60 80
model
SN 2005cf
SN 2003du
FIR0.9−2.4µm
FUV<0.35µm
FUV+IR
−10 0 10 20
0 100 200 300 400
Days from Bmax
MC ke+=10
p.i. model
no p.i. model
SN 2003du
Co decay
Fig. 14. a: The ratio between the UV and IR fluxes to the flux within
3500-9000 Å; b: The uvoir bolometric light curves of SN 2003du, SN
2006cf and best model. The inset shows an expansion of the SN 2003du
light curve and model around maximum; c: The entire uvoir bolometric
light curve with the models overplotted.
other hand is determined by the amount of 56Ni. Therefore, if the
fraction of stable Fe-group isotopes is varied within reasonable
limits (∼ 20%) the temperature may not be affected significantly,
and thus the opacity may be effectively unchanged. This would
lead to light curves with the same width, but different luminosi-
ties.
As shown in Fig. 14b, the uvoir ”bolometric” light curve
of SN 2003du is remarkably similar to that of SN 2005cf
(Pastorello et al., 2007b) if µ = 32.79 mag is adopted. Therefore,
a model similar to that adopted for SN 2005cf can be used also
to reproduce the light curve of SN 2003du. In this case the best
fit, shown in Fig. 14b, is obtained for a model with 0.69M⊙ of
56Ni and 0.42M⊙ of stable Fe-group isotopes using the W7 ex-
plosion model (Nomoto et al., 1984) as an input. This estimate
of the amount of 56Ni is in excellent agreement with the esti-
mate derived above using Arnett’s rule. However, mixing out of
a sufficient amount of 56Ni is necessary to reproduce the early
rise of the light curve. This is a feature that is not present in
one-dimensional explosion models, but is often inferred from
SN data. For example, for SN 2002bo, using the abundance dis-
tribution and the amount of 56Ni mixed out as derived from an
abundance tomography experiment (Stehle et al., 2005) gave a
much better reproduction of the bolometric light curve. What is
interpreted as mixing in one-dimensional models may be related
to the presence of high velocity features (Mazzali et al., 2005b),
which affect the early spectra of SN 2003du quite heavily.
If the true distance modulus were µ = 32.42, the light curve
could only be reproduced if the total mass of iron group elements
was the same as above (i.e. 1.11M⊙) but the
56Ni content was
∼ 0.45 M⊙. While this may still be a possibility, with such a low
56Ni mass (less than half of the total Fe-group content) it can be
expected that the heating by radioactive decay is not sufficient to
keep the gas at a sufficiently high temperature (∼ 104K) that the
opacity is unchanged. At lower temperatures, the opacity rapidly
drops (Khokhlov et al., 1993), and thus the light curve would not
be as broad as observed. We therefore suggest that a reasonable
range of distances for SN 2003du is between µ = 32.7 and 33.0
mag, implying a 56Ni mass between 0.6 and 0.8M⊙ for a total
Fe-group elements mass of ∼ 1.1M⊙.
Roughly 200 days after maximum SN Ia ejecta become
transparent to the γ-rays and the main source of energy is the
positrons produced by the decay of 56Co. If the positrons are
fully trapped and deposit all their kinetic energy, the true bolo-
metric LC should have a decline rate of ∼ 1 mag per 100 days.
Larger decline rates are typically found in SNe Ia, and assum-
ing that the optical flux follows the true bolometric flux, this
is usually interpreted as evidence for positron escape (see, e.g.,
Colgate et al., 1980; Cappellaro et al., 1997; Ruiz-Lapuente
& Spruit, 1998; Milne et al., 1999). The uvoir ”bolometric”
luminosity decline rate of SN 2003du after 200 days is 1.4
mag per 100 days. However, late-time NIR observations of few
SNe Ia have recently been published (SN 1998bu – Spyromilio
et al. 2004; SN 2000cx – Sollerman et al. 2004; SN 2004S –
Krisciunas et al. 2007) and indicate that after 300–350 days the
NIR luminosity does not decline but stays nearly constant. The
contribution of the NIR flux therefore increases with time and if
accounted for may lead to decline rates lower than the observed
ones and closer to the full positron trapping value. Motohara
et al. (2006) obtained late-time NIR spectra (1.1-1.8µm) and H-
band photometry of SN 2003du. At +330 days SN 2003du had
an H magnitude of 20.12±0.17 (Motohara et al. private commu-
nication) and we calculate the integrated flux across the H-band
to be ∼ 3% of the optical flux at that epoch. The late-time NIR
spectra of SN 2003du indicate that the integrated J and H band
fluxes are nearly equal, implying that the contribution of the NIR
flux is at least 6%. If we adopt a 10% NIR contribution at +330
days and assume that the total NIR flux did not change after-
wards, we obtain a decline rate of 1.2 mag per 100 days, which
is still larger than the full positron trapping value.
In Fig. 14c we compare the uvoir ”bolometric” LC of
SN 2003du with the two models presented by Sollerman et al.
(2004). The models are in the form of broadband U-to-H mag-
nitudes. For a consistent comparison with SN 2003du we used
only the UBVRI model fluxes to compute the model uvoir LC in
exactly the same way as for SN 2003du. The models are generic,
and have not been tuned to any particular SN. They have been
computed with 0.6M⊙
56Ni and assume full positron trapping,
and differ only in the treatment of the photoionization repre-
senting two extreme cases that the UV photons either escape
or are fully redistributed to lower energies (for more details see
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 15
Sollerman et al. 2004 and references therein). For a comparison
with SN 2003du the models were only re-scaled to a distance
modulus µ = 32.79 mag, and yet they fit the absolute flux level
of the LC of SN 2003du quite well. It is evident from Fig. 14c
that a model with an intermediate treatment of the photoion-
ization could reproduce the SN 2003du light curve. Figure 14c
also shows a model computed with the Monte Carlo code us-
ing the best parameters we estimated above. Only the opacity
to positrons kβ+ was adjusted to fit the late-time decline rate
(Cappellaro et al., 1997). The best value is kβ+ = 10 cm
−2 g−1,
which is well within the range of values found by Cappellaro
et al. (1997).
Both late-time LC models we discussed are based on the
1D W7 explosion model and do not include a contribution from
magnetic fields. However, detailed calculations (Ruiz-Lapuente
& Spruit, 1998; Milne et al., 1999) show that the positron depo-
sition rate is quite sensitive to the magnetic field configuration
in the ejecta and the actual explosion model. Clearly, to fully ex-
ploit the information in the bolometric LC a more detailed study
is needed, but this is beyond the scope of this paper.
4.4. Evolution of Si ii λ6355, Ca ii H&K and IR triplet
Figure 15 shows the pre-maximum evolution of the absorption
lines Si ii λ6355, Ca iiH&K and Ca ii IR3 in SN 2003du (here we
also use a few spectra of SN 2003du from Gerardy et al. 2004
and Anupama et al. 2005) and other SNe Ia. In the −13 days
spectrum of SN 2003du the Si ii λ6355 line is broad and rather
symmetric. In the −11 day spectrum the line is asymmetric and
narrower, but around a week before maximum becomes sym-
metric again and the profile does not change much until max-
imum. The line evolution in SN 1994D is very similar, but is
delayed with respect to SN 2003du: the −13 and −11 day spec-
tra of SN 2003du are most similar to those of SN 1994D at −11
and −9 days. Similar evolution is also observed in SN 2001el,
SN 1990N, SN 1999ee and SN 2005cg, but the pre-maximum
coverage of these SNe is rather sparse. Nevertheless, this profile
evolution may be explained if the Si ii λ6355 line is a blend of
two components. At 10− 14 days before maximum, the strength
of the two components should be nearly equal. The blue compo-
nent then decreases very rapidly, disappearing by ∼ 7 − 5 days
before maximum, while the red component increases in strength.
In SN 2003du, the blue component was last seen in the −7.8 day
spectrum as a weak feature on the blue wing of the line, and in
SN 2001el it may be still present in the −2 day spectrum. The
peculiar flat-bottom line shape in the early spectra of SN 2001el
and SN 1990N is thus due to the blue component extending over
a larger velocity interval compared to other SNe. The −9 day
spectrum of SN 1999ee on the other hand, has a stronger blue
component such that the line is asymmetric with an extended
red wing. Note that Mazzali (2001) and Mazzali et al. (2005b)
find that a two-component model is needed to explain the pe-
culiar Si ii λ6355 line shape in SN 1990N and SN 1999ee, the
high-velocity (HV) component being carbon/silicon and a thin
pure Si shell, respectively. It is also clear that the early-time evo-
lution of the blueshift of the line-profile minimum will be largely
determined by the evolution of relative strength of the two com-
ponents, and therefore will be very difficult to interpret.
Mattila et al. (2005) suggest that the flat-bottomed shape of
Si ii λ6355 in SN 2001el and its disappearance over a few days
can be explained by the effects of scattering within a thin re-
gion moving at the continuum photospheric velocity, thus re-
quiring no absorbing HV material to produce the line shape.
SN 2003du
-12.8
-10.9
SN 1994D
-12.0
-11.0
-10.2
SN 1990N
SN 2001el
SN 1999ee
SN 2005cg
-10.9
SN 2003du
Si II 3850?
-12.0
-11.0
-10.2
Si II    3850?
SN 1994D
SN 1998bu
Si II 3850?
SN 2001el -9
-20000 0
-10.9
SN 2003du
-20000 0
Velocity [km s-1]
SN 1994D
SN 2001el
-20000 0
SN 1998bu
Fig. 15. Comparison of the evolution of Si ii λ6355, Ca ii H&K and Ca ii
IR3 lines in SN 2003du with those of other normal SNe Ia.
Quimby et al. (2006) argue that the triangular shape of the pro-
file in SN 2005cg with an extended blue wing (see, Fig. 15) may
be due to absorption by Si in the HV part of the ejecta. The
line profile may be reproduced if the Si abundance slowly de-
creases toward high velocities, which is typical for the delayed-
detonation models (Khokhlov, 1991). However, these both sug-
gestions may have difficulties to explain asymmetric line pro-
files with a stronger blue component as observed in SN 1999ee.
SN 1999ee is not unique. SN 2005cf, observed by the ESC with
daily sampling starting from 12 days before maximum (Garavini
et al., 2007), shows Si ii λ6355 line that consists of two dis-
tinct components with profile evolution similar to SN 1999ee.
It is therefore likely that the ”peculiar” profiles in SN 2001el,
SN 1990N and SN 2005cg are just snapshots of this common
16 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
evolutionary pattern. In addition, if more SNe Ia like SN 2005cf
and SN 1999ee are found, the suggestion of Quimby et al. (2006)
that the SNe Ia with a flat-bottomed Si ii λ6355 line may consti-
tute a separate sub-class of SNe Ia, possibly produced from dif-
ferent progenitors and/or explosion models can be ruled out.
In the −11 day spectrum of SN 2003du the Ca ii H&K
line is a broad, single absorption with high velocity of
∼ −21000 km s−1. In the −7.8 days spectrum another, less
blueshifted Ca ii H&K component is also visible at velocity of
∼ −10000 km s−1. In the subsequent spectra, the HV compo-
nent decreases in strength, while the low-velocity one grows
stronger. Qualitatively the same evolution of also observed in
SN 1994D. In the near maximum spectra, the HV component
is much weaker, if present at all, in SN 1994D and SN 1998bu
than in SN 2003du and SN 2001el. It can be seen in Fig 15 that
the strength of the HV component in SN 1994D decreases faster
than in SN 2003du and SN 2001el, thus qualitatively following
the evolution of the Si ii λ6355 HV component. On the other
hand, SN 1998bu either lacked HV components altogether, or
they disappeared faster than in SN 1994D. The evolution of the
Ca ii IR3 line is shown for few epochs only, but it is evident
that a strong HV component with velocity of ∼ −21000 km s−1
is also present and that this component disappears at different
time, earliest in SN 1994D, followed by SN 2003du, and latest
in SN 2001el. It is also interesting to note that there is a segrega-
tion of SNe Ia according to Ca iiH&K line profile: (i) SNe with a
single-component line at all epochs, SN 2004S (Krisciunas et al.,
2007), SN 1999ee and SN 2002bo being examples, and (ii) SNe
like SN 2003du and SN 1994D with double-component line af-
ter maximum. In SN 1994D the blue component of the post-
maximum Ca ii H&K-split is already visible in the −9 spectrum
as a weak feature superimposed on the broad HV component,
while in SN 2003du it becomes apparent only around maximum,
possibly because the HV component remains visible longer than
in SN 1994D. Possible identification for this feature is Si ii λ3850
(Nugent et al., 1997; Lentz et al., 2000), which is also supported
by the identification of strong Si ii λ3850 line in the early spec-
trum of SN 2004dt (Wang et al., 2006).
Due to severe line blending it is difficult to quantify the
strength of the HV components at different epochs. However, the
qualitative comparison strongly suggests that the strength of the
HV components in the Si ii λ6355, Ca ii H&K and Ca ii IR3 line
in given SN are correlated and evolve similarly. The HV features
in the Ca ii lines are stronger and more separated from the lower-
velocity components than in the Si ii λ6355 line. Comprehensive
spectral modeling of the line profiles evolution is therefore
needed to verify the two-component hypothesis for Si ii λ6355
and further investigate the HV features (e.g. Mazzali et al.,
2005b). Such an analysis of the SN 2003du spectra will be pre-
sented elsewhere. Currently, there is no consensus on the origin
of the HV features. Interaction of the ejecta with circumstellar
matter close to the SN (e.g. Gerardy et al., 2004) or the clumpy
ejecta structure found in some explosion models (e.g., Mazzali
et al., 2005b; Plewa et al., 2004; Kasen & Plewa, 2005) could
cause the observed HV features. The continuum polarization in
SNe Ia is typically low, but much higher polarization across the
lines including the HV features is often observed, which favors
the clumpy ejecta model rather than a global asymmetry (Wang
et al., 2003a, 2006, 2007; Leonard et al., 2005). The HV features
may thus carry information about the 3D structure of the ejecta
and the environment close to the SN explosion site. Modeling
of time sequences of flux and polarization spectra (e.g., Kasen
et al., 2003; Thomas et al., 2004; Wang et al., 2007) may al-
low us to recover this information and help to impose additional
constraints on the SN Ia explosion and progenitor models.
5. Summary
We present an extensive set of optical and NIR observations of
the bright nearby Type Ia SN 2003du. The observations started
13 days before B-band maximum light, and continued for 480
days after with exceptionally good sampling. The optical pho-
tometry was performed after the background contamination
from the host galaxy had been removed by subtraction of tem-
plate images. The photometry was obtained using a number of
instruments with different filter responses. In order to properly
account for deviations from the standard system responses, the
optical photometry was calibrated by applying S-corrections.
Our observations show that the spectral and photometric
evolution of SN 2003du in both, optical and NIR wavelengths,
closely follow that of the normal SNe Ia. The luminosity decline
rate parameter ∆m15 is found to be 1.02 ±0.05, the ratio between
the depth of the Si ii λ5972 and λ6355 linesR(Si ii) = 0.22 ±0.02
and the velocity of the Si ii λ6355 line is ∼ −10000 km s−1
around maximum light. The analysis of the uvoir light curve sug-
gests that ∼ 0.6− 0.8 M⊙ of
56Ni was synthesized during the ex-
plosion. All this indicates an average normal SN Ia. We also find
that SN 2003du was unreddened in its host galaxy. This property
is important for better understanding of the intrinsic colors of
SNe Ia in order to obtain accurate estimates of the dust extinction
to the high-redshift SNe Ia, which is one of the major systematic
uncertainties in their cosmological use. SN 2003du also showed
strong high-velocity features in Ca ii H&K and Ca ii IR3 lines,
and possibly in Si ii λ6355. The excellent temporal coverage al-
lowed us to compare the time evolution of the line profiles with
other well-observed SNe Ia and we found evidence that the pe-
culiar pre-maximum evolution of Si ii λ6355 line in many SNe Ia
is due to the presence of two blended absorption components.
The well-sampled and carefully calibrated data set we
present is a significant addition to the well-observed SNe Ia and
the data will be made publicly available for further analysis. For
example comprehensive modeling of the extensive spectral data
set, e.g. by the abundance tomography method (Stehle et al.,
2005), may eventually help to achieve a better understanding of
the physics of SNe Ia explosions and their progenitors.
Acknowledgements. This work is partly supported by the European
Community’s Human Potential Program “The Physics of Type Ia Supernovae”,
under contract HPRN-CT-2002-00303. V.S. and A.G. would like to thank the
Göran Gustafsson Foundation for financial support. The work of D.Yu.T. and
N.N.P. was partly supported by the grant RFBR 05-02-17480. The work of S.M.
was supported by a EURYI scheme award.
This work is based on observations collected at the Italian Telescopio
Nazionale Galileo (TNG), Isaac Newton (INT) and William Herschel (WHT)
Telescopes, and Nordic Optical Telescope (NOT), all located at the Spanish
Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de
Canarias (La Palma, Spain), the 1.82m and 1.22m telescopes at Asiago (Italy),
the 2.2m and 3.5m telescopes at Calar Alto (Spain), the United Kingdom
Infrared Telescope (UKIRT) at Hawaii and the 60-cm telescope of the Beijing
Astronomical Observatory (China). We thank the support astronomers of these
telescopes for performing part of the observations. We also thank the director of
the Calar Alto Observatory Roland Gredel for allocating additional time at the
2.2m telescope in May 2003.
We thank all observers that gave up part of their time to observe SN 2003du.
Thomas Augusteijn and Amanda Djupvik are acknowledged for observing dur-
ing two technical nights at the NOT. Observations were also obtained at the
NOT during a student training course in Observational Astronomy provided
by Stockholm Observatory and the NorFA Summer School in Observational
Astronomy. We thank Geir Oye for excellent support and close collaboration dur-
ing this course. We also thank O.A.Burkhanov, S.Yu.Shugarov and I.M.Volkov
for carrying out observations at Maidanak, Slovakia, Moscow and Crimea. We
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 17
thank Cecilia Kozma for making available to us her late-time light curve mod-
els. We thank Aaron Barth for providing us with the spectra of SN 1994D col-
lected by the Alexei Filippenko group at UC Berkeley, and the people who did
the observations: Aaron Barth, Alexei Filippenko, Tomas Matheson, Xiaoming
Fan, Michael Gregg, Vesa Junkkarinen, Brian Espey, Matt Lehnert, Lee Armus,
Graeme Smith, Greg Wirth, David Koo, Abe Oren and Vince Virgilio. We thank
K. Motohara and the co-authors of Motohara et al. (2006) for providing us with
the unpublished late-time NIR magnitudes of SN 2003du.
This work has made use of the NASA/IPAC Extragalactic Database (NED),
the Lyon-Meudon Extragalactic Database (LEDA), NASA’s Astrophysics Data
System, the SIMBAD database operated at CDS, Strasbourg, France, data prod-
ucts from the Two Micron All Sky Survey and the SUSPECT supernova spectral
archive.
References
Alard, C. 2000, A&AS, 144, 363
Alard, C. & Lupton, R. H. 1998, ApJ, 503, 325
Anupama, G. C., Sahu, D. K., & Jose, J. 2005, A&A, 429, 667
Astier, P., Guy, J., Regnault, N., et al. 2006, A&A, 447, 31
Benetti, S., Cappellaro, E., Mazzali, P. A., et al. 2005, ApJ, 623, 1011
Benetti, S., Meikle, P., Stehle, M., et al. 2004, MNRAS, 348, 261
Bessell, M. S. 1990, PASP, 102, 1181
Bessell, M. S. 1995, PASP, 107, 672
Bessell, M. S., Castelli, F., & Plez, B. 1998, A&A, 333, 231
Branch, D., Garnavich, P., Matheson, T., et al. 2003, AJ, 126, 1489
Branch, D., Lacy, C. H., McCall, M. L., et al. 1983, ApJ, 270, 123
Branch, D. & Tammann, G. A. 1992, ARA&A, 30, 359
Branch, D., Thomas, R. C., Baron, E., et al. 2004, ApJ, 606, 413
Cappellaro, E., Mazzali, P. A., Benetti, S., et al. 1997, A&A, 328, 203
Colgate, S. A., Petschek, A. G., & Kriese, J. T. 1980, ApJ, 237, L81
Elias-Rosa, N., Benetti, S., Cappellaro, E., et al. 2006, MNRAS, 369, 1880
Filippenko, A. V. 1982, PASP, 94, 715
Filippenko, A. V. 1997, ARA&A, 35, 309
Garavini, G., Aldering, G., Amadon, A., et al. 2005, AJ, 130, 2278
Garavini, G., Folatelli, G., Goobar, A., et al. 2004, AJ, 128, 387
Garavini, G., Nobili, S., Taubenberger, S., et al. 2007, ArXiv Astrophysics e-
prints
Gerardy, C. L., Höflich, P., Fesen, R. A., et al. 2004, ApJ, 607, 391
Hamuy, M., Maza, J., Pinto, P. A., et al. 2002, AJ, 124, 417
Hamuy, M., Phillips, M. M., Maza, J., et al. 1995, AJ, 109, 1
Hamuy, M., Phillips, M. M., Suntzeff, N. B., et al. 1996, AJ, 112, 2391
Harris, W. E., Fitzgerald, M. P., & Reed, B. C. 1981, PASP, 93, 507
Hernandez, M., Meikle, W. P. S., Aparicio, A., et al. 2000, MNRAS, 319, 223
Hillebrandt, W. & Niemeyer, J. C. 2000, ARA&A, 38, 191
Hoeflich, P., Wheeler, J. C., & Thielemann, F. K. 1998, ApJ, 495, 617
Holschneider, M., Kronland-Martinet, R., Morlet, J., & Tchamitchian, P. 1989,
in Wavelets. Time-Frequency Methods and Phase Space, ed. J.-M. Combes,
A. Grossmann, & P. Tchamitchian, 286
Horne, K. 1986, PASP, 98, 609
Hunt, L. K., Mannucci, F., Testi, L., et al. 1998, AJ, 115, 2594
Iwamoto, K., Nakamura, T., Nomoto, K., et al. 2000, ApJ, 534, 660
Jeffery, D. J., Leibundgut, B., Kirshner, R. P., et al. 1992, ApJ, 397, 304
Jha, S., Garnavich, P. M., Kirshner, R. P., et al. 1999, ApJS, 125, 73
Jha, S., Kirshner, R. P., Challis, P., et al. 2006a, AJ, 131, 527
Jha, S., Riess, A. G., & Kirshner, R. P. 2006b, ArXiv Astrophysics e-prints
Karp, A. H., Lasher, G., Chan, K. L., & Salpeter, E. E. 1977, ApJ, 214, 161
Kasen, D., Nugent, P., Wang, L., et al. 2003, ApJ, 593, 788
Kasen, D. & Plewa, T. 2005, ApJ, 622, L41
Kasen, D. & Woosley, S. E. 2007, ApJ, 656, 661
Khokhlov, A., Mueller, E., & Hoeflich, P. 1993, A&A, 270, 223
Khokhlov, A. M. 1991, A&A, 245, 114
Kirshner, R. P., Jeffery, D. J., Leibundgut, B., et al. 1993, ApJ, 415, 589
Knop, R. A., Aldering, G., Amanullah, R., et al. 2003, ApJ, 598, 102
Kotak, R., Meikle, W. P. S., Pignata, G., et al. 2005, A&A, 436, 1021
Kotak, R., Meikle, W. P. S., & Rodriguez-Gil, P. 2003, IAU Circ., 8122, 3
Krisciunas, K., Garnavich, P. M., Stanishev, V., et al. 2007, AJ, 133, 58
Krisciunas, K., Hastings, N. C., Loomis, K., et al. 2000, ApJ, 539, 658
Krisciunas, K., Phillips, M. M., Stubbs, C., et al. 2001, AJ, 122, 1616
Krisciunas, K., Phillips, M. M., & Suntzeff, N. B. 2004a, ApJ, 602, L81
Krisciunas, K., Phillips, M. M., Suntzeff, N. B., et al. 2004b, AJ, 127, 1664
Krisciunas, K., Suntzeff, N. B., Candia, P., et al. 2003, AJ, 125, 166
Krisciunas, K., Suntzeff, N. B., Phillips, M. M., et al. 2004c, AJ, 128, 3034
Lair, J. C., Leising, M. D., Milne, P. A., & Williams, G. G. 2006, AJ, 132, 2024
Landolt, A. U. 1992, AJ, 104, 340
Leibundgut, B., Kirshner, R. P., Filippenko, A. V., et al. 1991, ApJ, 371, L23
Lentz, E. J., Baron, E., Branch, D., Hauschildt, P. H., & Nugent, P. E. 2000, ApJ,
530, 966
Leonard, D. C., Li, W., Filippenko, A. V., Foley, R. J., & Chornock, R. 2005,
ApJ, 632, 450
Majewski, S. R., Kron, R. G., Koo, D. C., & Bershady, M. A. 1994, PASP, 106,
Marion, G. H., Höflich, P., Vacca, W. D., & Wheeler, J. C. 2003, ApJ, 591, 316
Marion, G. H., Höflich, P., Wheeler, J. C., et al. 2006, ApJ, 645, 1392
Mattila, S., Lundqvist, P., Sollerman, J., et al. 2005, A&A, 443, 649
Mazzali, P. A. 2001, MNRAS, 321, 341
Mazzali, P. A., Benetti, S., Altavilla, G., et al. 2005a, ApJ, 623, L37
Mazzali, P. A., Benetti, S., Stehle, M., et al. 2005b, MNRAS, 357, 200
Mazzali, P. A., Iwamoto, K., & Nomoto, K. 2000, ApJ, 545, 407
Mazzali, P. A. & Lucy, L. B. 1998, MNRAS, 295, 428
Mazzali, P. A., Nomoto, K., Cappellaro, E., et al. 2001, ApJ, 547, 988
Mazzali, P. A. & Podsiadlowski, P. 2006, MNRAS, 369, L19
Meikle, W. P. S. 2000, MNRAS, 314, 782
Meikle, W. P. S., Cumming, R. J., Geballe, T. R., et al. 1996, MNRAS, 281, 263
Milne, P. A., The, L.-S., & Leising, M. D. 1999, ApJS, 124, 503
Motohara, K., Maeda, K., Gerardy, C. L., et al. 2006, ApJ, 652, L101
Nobili, S., Goobar, A., Knop, R., & Nugent, P. 2003, A&A, 404, 901
Nomoto, K., Thielemann, F.-K., & Yokoi, K. 1984, ApJ, 286, 644
Nugent, P., Baron, E., Branch, D., Fisher, A., & Hauschildt, P. H. 1997, ApJ,
485, 812
Nugent, P., Kim, A., & Perlmutter, S. 2002, PASP, 114, 803
Nugent, P., Phillips, M., Baron, E., Branch, D., & Hauschildt, P. 1995, ApJ, 455,
L147+
Pastorello, A., Mazzali, P. A., Pignata, G., et al. 2007a, ArXiv Astrophysics e-
prints
Pastorello, A., Taubenberger, S., Elias-Rosa, N., et al. 2007b, MNRAS, 161
Patat, F., Benetti, S., Cappellaro, E., et al. 1996, MNRAS, 278, 111
Pauldrach, A. W. A., Duschinger, M., Mazzali, P. A., et al. 1996, A&A, 312, 525
Peebles, P. J. & Ratra, B. 2003, Reviews of Modern Physics, 75, 559
Perlmutter, S., Aldering, G., Goldhaber, G., et al. 1999, ApJ, 517, 565
Phillips, M. M. 1993, ApJ, 413, L105
Phillips, M. M., Lira, P., Suntzeff, N. B., et al. 1999, AJ, 118, 1766
Pignata, G., Benetti, S., Buson, L., et al. 2005, in ASP Conf. Ser. 342: 1604-
2004: Supernovae as Cosmological Lighthouses, ed. M. Turatto, S. Benetti,
L. Zampieri, & W. Shea, 266
Pignata, G., Patat, F., Benetti, S., et al. 2004, MNRAS, 355, 178
Pinto, P. A. & Eastman, R. G. 2000, ApJ, 530, 757
Plewa, T., Calder, A. C., & Lamb, D. Q. 2004, ApJ, 612, L37
Prieto, J. L., Rest, A., & Suntzeff, N. B. 2006, ApJ, 647, 501
Pskovskii, I. P. 1977, Soviet Astronomy, 21, 675
Quimby, R., Höflich, P., Kannappan, S. J., et al. 2006, ApJ, 636, 400
Riess, A. G., Filippenko, A. V., Challis, P., et al. 1998, AJ, 116, 1009
Riess, A. G., Li, W., Stetson, P. B., et al. 2005, ApJ, 627, 579
Riess, A. G., Press, W. H., & Kirshner, R. P. 1995, ApJ, 445, L91
Riess, A. G., Strolger, L.-G., Casertano, S., et al. 2007, ApJ, 659, 98
Riess, A. G., Strolger, L.-G., Tonry, J., et al. 2004, ApJ, 607, 665
Röpke, F. K., Gieseler, M., Reinecke, M., Travaglio, C., & Hillebrandt, W. 2006,
A&A, 453, 203
Röpke, F. K. & Hillebrandt, W. 2004, A&A, 420, L1
Rudy, R. J., Lynch, D. K., Mazuk, S., et al. 2002, ApJ, 565, 413
Ruiz-Lapuente, P. & Spruit, H. C. 1998, ApJ, 500, 360
Salvo, M. E., Cappellaro, E., Mazzali, P. A., et al. 2001, MNRAS, 321, 254
Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ, 500, 525
Schwartz, M. & Holvorcem, P. R. 2003, IAU Circ., 8121, 1
Sollerman, J., Lindahl, J., Kozma, C., et al. 2004, A&A, 428, 555
Spyromilio, J., Gilmozzi, R., Sollerman, J., et al. 2004, A&A, 426, 547
Stehle, M., Mazzali, P. A., Benetti, S., & Hillebrandt, W. 2005, MNRAS, 360,
Stetson, P. B. 2000, PASP, 112, 925
Stritzinger, M., Hamuy, M., Suntzeff, N. B., et al. 2002, AJ, 124, 2100
Stritzinger, M. & Leibundgut, B. 2005, A&A, 431
Stritzinger, M., Mazzali, P. A., Sollerman, J., & Benetti, S. 2006, A&A, 460, 793
Stritzinger, M., Suntzeff, N. B., Hamuy, M., et al. 2005, PASP, 117, 810
Suntzeff, N. B. 1996, in IAU Colloq. 145: Supernovae and Supernova Remnants,
ed. R. McCray & Z. Wang, 41
Suntzeff, N. B. 2000, in American Institute of Physics Conference Series, ed.
S. S. Holt & W. W. Zhang, 65–74
Thomas, R. C., Branch, D., Baron, E., et al. 2004, ApJ, 601, 1019
Timmes, F. X., Brown, E. F., & Truran, J. W. 2003, ApJ, 590, L83
Tokunaga, A. T., Simons, D. A., & Vacca, W. D. 2002, PASP, 114, 180
Umeda, H., Nomoto, K., Kobayashi, C., Hachisu, I., & Kato, M. 1999, ApJ, 522,
van Dokkum, P. G. 2001, PASP, 113, 1420
Wade, R. A. & Horne, K. 1988, ApJ, 324, 411
18 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
Wang, L., Baade, D., Höflich, P., et al. 2003a, ApJ, 591, 1110
Wang, L., Baade, D., Höflich, P., et al. 2006, ApJ, 653, 490
Wang, L., Baade, D., & Patat, F. 2007, Science, 315, 212
Wang, L., Goldhaber, G., Aldering, G., & Perlmutter, S. 2003b, ApJ, 590, 944
Wells, L. A., Phillips, M. M., Suntzeff, B., et al. 1994, AJ, 108, 2233
Wheeler, J. C., Hoeflich, P., Harkness, R. P., & Spyromilio, J. 1998, ApJ, 496,
Wood-Vasey, W. M., Miknaitis, G., Stubbs, C. W., et al. 2007, ArXiv
Astrophysics e-prints
Appendix A: S-corrections
A.1. Photometric systems responses
The most important ingredient for computing S-corrections is
the accurate knowledge of the object SED and the response of
the instruments used. Pignata et al. (2004) have calculated the
responses of most of the instruments used by the ESC. However,
we repeated the process for the 5 instruments most frequently
used to observe SN 2003du: AFOSC at Asiago 1.82m telescope,
DOLORES at TNG, ALFOSC at NOT, CAFOS at Calar Alto
2.2m telescope and BAO 60-cm telescope imager, using the new
extensive spectrophotometry of Landolt stars in Stritzinger et al.
(2005). The first four of the five instruments are combined spec-
trographs/imagers with design that allows the grisms, the slits
and the imaging filters to be inserted into the light beam simul-
taneously. This made possible to measure the filter transmissions
in situ as the filters are mounted in the instrument and used dur-
ing the photometric observations. This measurement is straight-
forward and consists of taking spectral flat-fields with and with-
out the filter in the beam. The flat taken with the filter is divided
by the one taken without, giving the filter transmission. Before
doing this, the bias and any reflected light present was carefully
removed. The latter can be important in the blue part of the spec-
trum where the sensitivity of the system is low and the scattered
light can be a significant fraction of the useful signal; this can af-
fect the measured transmission. The wavelength calibration was
done with arc-lamp spectra taken without the filter in the beam.
When filters are introduced in the beam small shifts of the wave-
length solution can be expected. After the measurements we
checked this for few filters at AFOSC at Asiago 1.8m telescope
and did indeed find shifts of a few pixels. Hence, the measured
filter transmissions might be shifted by up to 20–30 Å, but the
shape is accurately determined. Generally, we found good agree-
ment with the filter transmissions available from the instrument
web-pages. However, we found significant discrepancies for the
Calar Alto 2.2m + CAFOS B and I filters, and minor differences
for the TNG+DOLORS I-band. For the U-bands we used the
transmissions available from the instrument web-pages. For the
BAO 60-cm telescope the filter transmissions specified by the
manufacturer were used.
The total system responses were computed by multiplying
the filter transmissions by (a) the CCD quantum efficiency (QE),
(b) the reflectivity of at least two aluminum surfaces, (c) the
continuum transmission of the Earth atmosphere at airmass one
(the extinction laws were provided by the observatories), and
(d) a telluric absorption spectrum, which we derived from the
spectrophotometric standards observed at WHT close to airmass
one. The lens and window transmissions were not included be-
cause this information was unavailable. Synthetic magnitudes
were calculated from Stritzinger et al. (2005) spectrophotometry
of Landolt standard stars, msyn = −2.5 log
f phot
(λ)Rnat(λ)dλ
The difference between the synthetic and the observed photome-
try was fitted as a function of the observed color indices to com-
pute synthetic color-terms (ctsyn), e.g. for B we have
Bstd − Bsyn = ctsyn(Bstd − V std) + const. (A.1)
For the VRI-bands, the ctsyn’s were close to the observed ones
ctobs. In some cases small differences exceeding the uncertainty
were accounted for by shifting the filter transmissions until ctsyn
matched ctosb. Small shifts of up to ∼ 20 − 30 Å were required.
These discrepancies could easily have arisen from the way in
which the transmissions were determined, as discussed above.
For the U and B-bands however, we found large differences
which would have required an unacceptably large shift to cor-
rect for them. The synthetic U and B bands were always too blue.
This is, to some extent, to be expected because the neglected op-
tical elements like lenses or windows, anti-reflection and other
coatings will tend to reduce the system sensitivity shortward of
∼4000 Å. The uncertainty in the CCD QEs and the extinction
laws may also contribute to this effect. To account for the net
effect of these uncertainties we modified the U and B bands by
multiplying them with a smooth monotonic function of wave-
length so that ctsyn matched ctobs. We used the Sigmoid function
F(λ; λ0,∆) =
1 + exp(−(λ − λ0)/∆)
, (A.2)
that changes smoothly from 0 to 1. The parameters λ0 and ∆
control the position and the width of the transition; for small
∆ the Sigmoid function approaches a Heaviside step function
at λ0. We proceeded as follows: λ0 and ∆ were varied in the
wavelength intervals 3200–4200Å and 100–500 Å, respectively,
and the set of parameters that brought the synthetic U and B-
band color-terms into accord with the observed ones was chosen.
Note that independent modification of U and B results in degen-
eracy in the (λ0,∆) parameter space, and it was only when the
U and B-bands were considered together that an unique solution
for λ0 and ∆ could be obtained. As standard Johnson-Cousins
system responses we use the Bessell (1990) filters but following
Stritzinger et al. (2005) we first modified them so that they could
be used with photon fluxes and included the telluric absorptions.
Small shifts were also applied to account for the small color-
terms that are noticeable when compared with the Landolt pho-
tometry. Bessell (1995) suggested correcting Landolt photome-
try to bring it into the original Cousins system. The synthetic
photometry with the original Bessell filters does match the cor-
rected magnitudes. However, for sake of comparability with the
existing SN photometry, we use the original Landolt photometry
and modify the Bessell filters so that the synthetic color-terms
are zero. The constant terms derived from the fits with Eq. A.1
are the filter zero-points for synthetic photometry. The constant
in Eq. 2 is the difference between the zero-point for the Bessell
and natural passbands.
The reconstructed bands are shown in Fig. A.1 together with
the modified Bessell filters, demonstrating the variety of pass-
bands one may encounter at different telescopes. Note particu-
larly the non-standard form of the Calar Alto I-band and NOT
R-band. We note that the reconstructed responses should be re-
garded only as approximations of the real responses. A given
passband can be modified in many ways to match the observed
and the synthetic color-term, and we would consider the pro-
cedure we used as the most appropriate one given the available
information. We also note that fitting the U-band synthetic color-
term is ambiguous. Because of the Balmer discontinuity even
small deviation from the Bessell passband changes U std − U syn
such that it needs no longer be a simple linear function of
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 19
4000 6000 8000 10000
Wavelength [Å]
modified Bessell Asiago            TNG             NOT             Calar Alto                BAO
U          B                V            R                                     I
Fig. A.1. Reconstructed system responses for the five instruments studied compared to the modified Bessell passbands.
U std−Bstd. This also affects the derivation of the observed color-
terms and as a result the U-band photometry should be in general
considered significantly less accurate than other bands.
A.2. Computing the S-corrections
We used our spectra obtained earlier than 110 days after max-
imum, and spectra from Gerardy et al. (2004) and Anupama
et al. (2005) to compute the S-corrections and to transform
the BVRI photometry of SN 2003du into the Johnson-Cousins
system. The TNG, Calar Alto and BAO I-bands extend out to
1.1 µm and to compute the S-corrections, we also used our NIR
spectra of SN 2003du (Sec. 2.3). To compute the BAO I-band S-
corrections between +30 and +63 days we also used NIR spectra
of SN 1999ee (Hamuy et al., 2002) and SN 2000ca (Stanishev et
al., in preparation) taken at ∼ +40 days. The U-band could not
be S-corrected because no UV spectra of SN 2003du were avail-
able.
The relative spectrophotometry of SN 2003du was not al-
ways sufficiently accurate for the purpose of computing S-
corrections. It was thus necessary to slightly modify some of
the spectra so that the synthetic photometry with the modified
Bessell BVRI bands matched the observed one. To achieve that,
the spectra were multiplied by a smooth correction function de-
termined by fitting the ratio between the observed and the syn-
thetic fluxes. When the ratio varied monotonically with wave-
length, a second-order polynomial was used. When a more com-
plex function was required, a spline fit was used. At the first it-
eration the synthetic magnitudes were compared with the linear
color-term corrected magnitudes of SN 2003du, and the spectra
were only modified if the observed and the synthetic color in-
dices differed by more than 0.05 mag for B − V and V − R, and
0.1 mag for V − I. These corrected spectra were used to compute
S-corrected photometry of SN 2003du. The flux correction of the
spectra was then repeated using the S-corrected rather than the
color-term corrected photometry. Spectra were only corrected if
the color discrepancies were greater than 0.03 mag for B − V
and V − R, or 0.05 mag for V − I. New S-corrected photome-
try was then computed and the process repeated to obtain the
final S-corrected photometry and calibrated spectra. A number
of spectra have a wavelength coverage that only allows B and V
synthetic magnitudes to be computed. In these cases, only a sim-
ple linear correction was applied to match the observed B and V
magnitudes.
We note that because the instrumental responses are fairly
close to those of Bessell filters, the S-corrections are almost en-
tirely determined by the SN spectral features and are practically
insensitive to small changes of the SN colors. It was found that
the initial correction of the spectra yielded spectrophotometry
which was already accurate to a few per cent and that the subse-
quent iterations had very little effect on the final calibrated pho-
tometry. We therefore conclude that the few percent uncertain-
ties in the spectrophotometry, which might have arisen from the
way the spectra were corrected, should have little effect on the
final photometry.
List of Objects
‘SN 2003du’ on page 1
‘SN 2003du’ on page 1
‘UGC 9391’ on page 1
‘SN 2003du’ on page 1
‘SN 2003du’ on page 1
‘SN 2003du’ on page 2
‘UGC 9391’ on page 2
‘SN 2003du’ on page 2
‘SN 2002bo’ on page 2
‘SN 2002dj’ on page 2
‘SN 2002er’ on page 2
‘SN 2003cg’ on page 2
‘SN 2004eo’ on page 2
‘SN 2005cf’ on page 2
‘SN 2003du’ on page 2
‘SN 2003du’ on page 2
‘SN 2003du’ on page 2
‘SN 2003du’ on page 3
‘SN 2003du’ on page 3
‘SN 2003du’ on page 3
‘SN 2003du’ on page 3
‘M92’ on page 4
‘SN 2003du’ on page 4
‘SN 2003du’ on page 4
‘SN 2003du’ on page 4
‘SN 2003du’ on page 4
‘SN 2003du’ on page 5
‘SN 2003du’ on page 5
‘SN 2003du’ on page 5
‘SN 2003du’ on page 5
20 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
‘SN 2003du’ on page 5
‘SN 2003du’ on page 6
‘SN 2003du’ on page 6
‘SN 2003du’ on page 6
‘SN 2003du’ on page 6
‘SN 2003du’ on page 7
‘SN 2000cx’ on page 7
‘SN 2003du’ on page 7
‘1990N’ on page 7
‘1998aq’ on page 7
‘1998bu’ on page 7
‘SN 2003du’ on page 7
‘SN 2003du’ on page 7
‘SN 2003du’ on page 7
‘SN 2003du’ on page 8
‘SN 2003du’ on page 8
‘SN 2003du’ on page 8
‘SN 2003du’ on page 8
‘SN 2003du’ on page 8
‘SN 2003du’ on page 8
‘SN 2003du’ on page 8
‘SN 2003du’ on page 8
‘SN 2003du’ on page 8
‘SN 2003du’ on page 8
‘SN 2003du’ on page 9
‘SN 2003du’ on page 9
‘SN 1994D’ on page 9
‘SN 1990N’ on page 9
‘SN 1996X’ on page 9
‘SN 1999ee’ on page 9
‘SN 1998aq’ on page 9
‘SN 1998bu’ on page 9
‘SN 2002er’ on page 9
‘SN 2001el’ on page 9
‘SN 2003du’ on page 10
‘SN 2003du’ on page 10
‘SN 1998bu’ on page 10
‘SN 2005cg’ on page 10
‘SN 2003du’ on page 10
‘SN 2003du’ on page 10
‘SN 2000cx’ on page 10
‘SN 2003du’ on page 10
‘SN 1994D’ on page 10
‘SN 2003du’ on page 11
‘SN 1999ee’ on page 11
‘SN 1998bu’ on page 11
‘SN 2002bo’ on page 11
‘SN 2002bo’ on page 11
‘SN 2003du’ on page 11
‘SN 2003du’ on page 11
‘SN 2003du’ on page 11
‘SN 2003du’ on page 11
‘SN 2003du’ on page 11
‘SN 2003du’ on page 12
‘SN 2003du’ on page 12
‘UGC 9391’ on page 12
‘SN 2003du’ on page 12
‘SN 1998aq’ on page 12
‘SN 1994ae’ on page 12
‘SN 2003du’ on page 12
‘SN 2003du’ on page 12
‘SN 2003du’ on page 12
‘SN 2003du’ on page 12
‘SN 2003du’ on page 13
‘UGC 9391’ on page 13
‘UGC 9391’ on page 13
‘SN 2003du’ on page 13
‘SN 2003du’ on page 13
‘SN 2001el’ on page 13
‘SN 2003du’ on page 13
‘SN 2003du’ on page 13
‘SN 1990N’ on page 13
‘SN 1989B’ on page 13
‘SN 1981B’ on page 13
‘SN 1992A’ on page 13
‘SN 2001el’ on page 13
‘SN 2003du’ on page 13
‘SN 2001el’ on page 13
‘SN 2003du’ on page 13
‘SN 2003du’ on page 13
‘SN 2005cf’ on page 13
‘SN 2003du’ on page 13
‘SN 2003du’ on page 13
‘SN 2003du’ on page 13
‘SN 2003du’ on page 13
‘SN 2003du’ on page 13
‘SN 2003du’ on page 14
‘SN 2006cf’ on page 14
‘SN 2003du’ on page 14
‘SN 2003du’ on page 14
‘SN 2005cf’ on page 14
‘SN 2005cf’ on page 14
‘SN 2003du’ on page 14
‘SN 2002bo’ on page 14
‘SN 2003du’ on page 14
‘SN 2003du’ on page 14
‘SN 2003du’ on page 14
‘SN 1998bu’ on page 14
‘SN 2000cx’ on page 14
‘SN 2004S’ on page 14
‘SN 2003du’ on page 14
‘SN 2003du’ on page 14
‘SN 2003du’ on page 14
‘SN 2003du’ on page 14
‘SN 2003du’ on page 14
‘SN 2003du’ on page 14
‘SN 2003du’ on page 15
‘SN 2003du’ on page 15
‘SN 2003du’ on page 15
‘SN 2003du’ on page 15
‘SN 2003du’ on page 15
‘SN 2003du’ on page 15
‘SN 1994D’ on page 15
‘SN 2003du’ on page 15
‘SN 2003du’ on page 15
‘SN 1994D’ on page 15
‘SN 2001el’ on page 15
‘SN 1990N’ on page 15
‘SN 1999ee’ on page 15
‘SN 2005cg’ on page 15
‘SN 2003du’ on page 15
‘SN 2001el’ on page 15
‘SN 2001el’ on page 15
‘SN 1990N’ on page 15
‘SN 1999ee’ on page 15
‘SN 1990N’ on page 15
‘SN 1999ee’ on page 15
‘SN 2001el’ on page 15
Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova 21
‘SN 2003du’ on page 15
‘SN 2005cg’ on page 15
‘SN 1999ee’ on page 15
‘SN 1999ee’ on page 15
‘SN 2005cf’ on page 15
‘SN 1999ee’ on page 15
‘SN 2001el’ on page 15
‘SN 1990N’ on page 15
‘SN 2005cg’ on page 15
‘SN 2005cf’ on page 16
‘SN 1999ee’ on page 16
‘SN 2003du’ on page 16
‘SN 1994D’ on page 16
‘SN 1994D’ on page 16
‘SN 1998bu’ on page 16
‘SN 2003du’ on page 16
‘SN 2001el’ on page 16
‘SN 1994D’ on page 16
‘SN 2003du’ on page 16
‘SN 2001el’ on page 16
‘SN 1998bu’ on page 16
‘SN 1994D’ on page 16
‘SN 1994D’ on page 16
‘SN 2003du’ on page 16
‘SN 2001el’ on page 16
‘SN 2004S’ on page 16
‘SN 1999ee’ on page 16
‘SN 2002bo’ on page 16
‘SN 2003du’ on page 16
‘SN 1994D’ on page 16
‘SN 1994D’ on page 16
‘SN 2003du’ on page 16
‘SN 1994D’ on page 16
‘SN 2004dt’ on page 16
‘SN 2003du’ on page 16
‘SN 2003du’ on page 16
‘SN 2003du’ on page 16
‘SN 2003du’ on page 16
‘SN 2003du’ on page 16
‘SN 2003du’ on page 18
‘SN 2003du’ on page 19
‘SN 2003du’ on page 19
‘SN 1999ee’ on page 19
‘SN 2000ca’ on page 19
‘SN 2003du’ on page 19
‘SN 2003du’ on page 19
‘SN 2003du’ on page 19
‘SN 2003du’ on page 19
‘SN 2003du’ on page 22
22 Stanishev et al.: SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
Table 3. Optical photometry SN 2003du. The measurements on the dates marked with ”∗” and all U magnitudes are not S-corrected.
Date (UT) Phase [day] JD U B V R I Telescope
2003-04-25 −11.0 2452755.39 · · · 14.737 (0.018) 14.854 (0.014) 14.728 (0.010) 14.798 (0.017) AS1.8
2003-04-25 −10.8 2452755.61 14.382 (0.011) 14.629 (0.010) 14.774 (0.010) 14.672 (0.010) 14.756 (0.021) NOT
2003-04-29 −7.3 2452759.06 · · · 13.974 (0.014) 14.072 (0.022) 13.963 (0.015) 14.052 (0.017) BAO
2003-04-30 −6.2 2452760.17 · · · 13.820 (0.024) 13.920 (0.012) 13.852 (0.010) 13.936 (0.024) BAO
2003-04-30 −5.8 2452760.54 13.193 (0.034) 13.719 (0.018) 13.860 (0.010) 13.754 (0.010) 13.921 (0.021) TNG
2003-05-02 −4.0 2452762.38 13.077 (0.015) 13.589 (0.021) 13.712 (0.027) 13.639 (0.022) 13.834 (0.023) TNG
2003-05-04 −1.9 2452764.46 · · · 13.496 (0.010) 13.614 (0.018) 13.592 (0.010) 13.841 (0.010) AS1.8
2003-05-05 −1.0 2452765.41 · · · 13.489 (0.012) 13.595 (0.019) 13.569 (0.010) 13.857 (0.011) AS1.8
2003-05-06 +0.0 2452766.40 · · · 13.489 (0.019) 13.566 (0.025) 13.575 (0.011) 13.870 (0.010) AS1.8
2003-05-07 +1.1 2452767.51 · · · 13.506 (0.015) 13.575 (0.014) 13.590 (0.018) 13.927 (0.016) AS1.8
2003-05-09 +3.1 2452769.51 · · · 13.566 (0.010) 13.587 (0.021) 13.600 (0.010) 14.009 (0.010) AS1.8
2003-05-10 +4.2 2452770.61 13.234 (0.014) 13.605 (0.010) 13.620 (0.016) 13.600 (0.010) 13.982 (0.016) CA2.2
2003-05-11 +5.1 2452771.51 13.316 (0.040) 13.643 (0.011) 13.642 (0.017) · · · 14.017 (0.010) CA2.2
2003-05-13 +7.2 2452773.59 13.597 (0.021) 13.764 (0.010) 13.712 (0.010) 13.786 (0.011) 14.205 (0.018) NOT
2003-05-14 +8.2 2452774.56 13.651 (0.017) 13.845 (0.011) 13.758 (0.010) 13.838 (0.010) 14.271 (0.010) NOT
2003-05-15 +9.1 2452775.44 13.749 (0.017) 13.908 (0.010) 13.795 (0.011) 13.908 (0.011) 14.352 (0.015) NOT
2003-05-16 +10.1 2452776.45 13.838 (0.021) 14.004 (0.014) 13.842 (0.010) 13.979 (0.010) 14.443 (0.011) NOT
2003-05-17 +10.7 2452777.08 · · · 14.066 (0.018) 13.862 (0.010) 14.040 (0.011) 14.448 (0.010) BAO
2003-05-22 +15.8 2452782.20 · · · 14.596 (0.013) 14.186 (0.010) 14.342 (0.011) 14.588 (0.017) BAO
2003-05-23 +17.1 2452783.49 · · · 14.722 (0.023) 14.268 (0.028) 14.332 (0.012) 14.626 (0.031) AS1.8
2003-05-24 +18.0 2452784.42 · · · 14.833 (0.014) 14.302 (0.014) 14.350 (0.016) 14.611 (0.010) AS1.8
2003-05-25 +19.0 2452785.37 · · · 14.942 (0.012) 14.350 (0.013) 14.361 (0.012) 14.594 (0.010) AS1.8
2003-05-26 +20.0 2452786.38 · · · 15.043 (0.011) · · · · · · · · · CA2.2
2003-05-27 +21.0 2452787.45 15.144 (0.017) 15.146 (0.014) 14.463 (0.017) 14.392 (0.012) 14.464 (0.018) CA2.2
2003-05-29 +22.8 2452789.20 · · · · · · · · · 14.493 (0.031) 14.451 (0.014) BAO
2003-06-01 +26.1 2452792.51 15.809 (0.023) 15.648 (0.010) 14.724 (0.010) 14.453 (0.019) 14.410 (0.027) TNG
2003-06-06 +31.2 2452797.58 16.172 (0.033) 16.041 (0.011) 15.018 (0.014) 14.658 (0.010) 14.451 (0.019) TNG
2003-06-10 +34.7 2452801.06 · · · 16.363 (0.085) 15.223 (0.047) 14.881 (0.018) 14.540 (0.035) BAO
2003-06-14 +38.7 2452805.04 · · · · · · 15.477 (0.131) 15.140 (0.013) 14.829 (0.024) BAO
2003-06-15 +39.7 2452806.04 · · · 16.472 (0.036) 15.473 (0.011) 15.187 (0.018) 14.929 (0.018) BAO
2003-06-20 +45.1 2452811.51 · · · 16.606 (0.021) 15.676 (0.010) 15.415 (0.017) 15.265 (0.010) AS1.8
2003-06-26 +51.1 2452817.52 16.796 (0.023) 16.727 (0.011) 15.859 (0.015) 15.613 (0.011) 15.584 (0.022) TNG
2003-06-28 +52.7 2452819.04 · · · 16.745 (0.023) 15.892 (0.012) 15.679 (0.018) 15.633 (0.038) BAO
2003-06-30 +54.6 2452821.03 · · · 16.753 (0.039) 15.924 (0.018) 15.776 (0.032) 15.715 (0.039) BAO
2003-07-04 +58.7 2452825.06 · · · 16.835 (0.016) 16.046 (0.019) 15.874 (0.011) 15.920 (0.022) BAO
2003-07-05 +60.0 2452826.38 · · · · · · 16.088 (0.016) 15.926 (0.010) 16.026 (0.019) NOT
2003-07-08 +62.7 2452829.06 · · · · · · 16.159 (0.036) 16.010 (0.017) 16.096 (0.029) BAO
2003-07-08 +63.1 2452829.53 17.004 (0.026) 16.924 (0.011) 16.173 (0.010) 16.036 (0.011) 16.138 (0.017) NOT
2003-07-09 +63.7 2452830.06 · · · · · · · · · · · · 16.194 (0.045) BAO
2003-07-12∗ +66.8 2452833.19 · · · · · · 16.290 (0.020) 16.140 (0.020) 16.270 (0.030) MDK
2003-07-17 +72.0 2452838.33 · · · 17.082 (0.015) 16.410 (0.015) 16.275 (0.010) 16.477 (0.012) AS1.8
2003-08-01 +87.0 2452853.34 · · · 17.319 (0.010) 16.769 (0.011) 16.719 (0.011) 17.010 (0.011) AS1.8
2003-08-22 +108.0 2452874.40 · · · 17.618 (0.030) 17.266 (0.026) 17.309 (0.028) · · · AS1.8
2003-08-23 +109.0 2452875.37 · · · 17.688 (0.011) 17.281 (0.012) 17.379 (0.014) 17.756 (0.018) AS1.8
2003-09-16∗ +132.9 2452899.32 18.763 (0.079) 17.961 (0.022) 17.780 (0.021) 18.040 (0.023) 18.454 (0.075) CA2.2
2003-09-19∗ +136.0 2452902.38 18.844 (0.032) 18.059 (0.012) 17.851 (0.017) 18.077 (0.029) 18.329 (0.020) WHT
2003-09-26∗ +143.0 2452909.34 19.140 (0.072) 18.114 (0.021) 17.956 (0.043) 18.330 (0.062) 18.570 (0.067) CA2.2
2003-11-22∗ +199.2 2452965.62 · · · 18.660 (0.100) 18.670 (0.100) 19.090 (0.120) · · · CRM
2003-11-23∗ +200.3 2452966.63 · · · 18.990 (0.060) 18.930 (0.060) 19.210 (0.110) · · · CRM
2003-11-25∗ +202.2 2452968.61 · · · 18.900 (0.040) 18.950 (0.050) 19.330 (0.110) · · · CRM
2003-12-01∗ +208.3 2452974.63 · · · 19.020 (0.070) 19.090 (0.100) 19.370 (0.120) · · · CRM
2003-12-12∗ +220.4 2452986.75 20.688 (0.038) 19.304 (0.016) 19.313 (0.012) 19.899 (0.041) 19.673 (0.031) CA3.5
2003-12-19∗ +227.4 2452993.75 · · · 19.384 (0.010) 19.419 (0.011) 19.979 (0.044) 19.910 (0.033) CA3.5
2004-05-10∗ +370.2 2453136.62 · · · 21.476 (0.019) 21.453 (0.020) 22.202 (0.044) 21.192 (0.029) WHT
2004-05-11∗ +371.2 2453137.62 22.638 (0.079) 21.531 (0.011) 21.493 (0.018) 22.190 (0.028) 21.320 (0.030) WHT
2004-06-22∗ +413.4 2453179.54 · · · 22.100 (0.044) 22.010 (0.026) 23.010 (0.052) 21.720 (0.038) NOT
2004-08-11∗ +463.0 2453229.43 · · · 22.771 (0.027) 22.827 (0.026) · · · · · · NOT
2004-08-14∗ +466.0 2453232.39 · · · · · · · · · · · · 22.212 (0.048) TNG
AS1.8 – Asiago 1.82m + AFOSC; NOT – Nordic Optical Telescope + ALFOSC; CA2.2 – Calar Alto 2.2m + CAFOS; TNG – Telescopio
Nazionale Galileo + DOLORES; WHT – William Herschel Telescope + PFIP; CA3.5 – Calar Alto 3.5m + LAICA; BAO – Beijing Astronomical
Observatory 60cm + CCD; MDK – Maidanak Observatory 1.5m + SITe CCD; CRM – 60-cm Crimean reflector + CCD.
