Accepted to the Astronomical Journal
Preprint typeset using LATEX style emulateapj v. 5/2/11

INTEGRAL FIELD SPECTROSCOPY OF SUPERNOVA EXPLOSION SITES: CONSTRAINING MASS ANDMETALLICITY OF THE PROGENITORS - I. TYPE IB AND IC SUPERNOVAE
Hanindyo Kuncarayakti

arXiv:1305.1105v1 [astro-ph.CO] 6 May 2013

Kavli Institute for the Physics and Mathematics of the Universe, the University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583,
Japan
Institute of Astronomy, Graduate School of Science, the University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan and
Department of Astronomy, Graduate School of Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Mamoru Doi
Institute of Astronomy, Graduate School of Science, the University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan andResearch Center for the Early Universe, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Greg Aldering
Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720

Nobuo Arimoto
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan andSubaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 96720

Keiichi Maeda
Kavli Institute for the Physics and Mathematics of the Universe, the University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583,
Japan

Tomoki Morokuma
Institute of Astronomy, Graduate School of Science, the University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan

Rui Pereira
CNRS/IN2P3, Institut de Physique Nucléaire de Lyon, 4 Rue Enrico Fermi, 69622 Villeurbanne Cedex, France

Tomonori Usuda
Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 96720

Yasuhito Hashiba
Institute of Astronomy, Graduate School of Science, the University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan and
Department of Astronomy, Graduate School of Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Accepted to the Astronomical Journal

ABSTRACT
Integral field spectroscopy of 11 type-Ib/c supernova explosion sites in nearby galaxies has beenobtained using UH88/SNIFS and Gemini-N/GMOS. The use of integral field spectroscopy enables us
to obtain both spatial and spectral information of the explosion site, allowing the identification of theparent stellar population of the supernova progenitor star. The spectrum of the parent population
provides metallicity determination via strong-line method and age estimation obtained via comparison
with simple stellar population (SSP) models. We adopt this information as the metallicity and age ofthe supernova progenitor, under the assumption that it was coeval with the parent stellar population.
The age of the star corresponds to its lifetime, which in turn gives the estimate of its initial mass.
With this method we were able to determine both the metallicity and initial (ZAMS) mass of theprogenitor stars of the type Ib and Ic supernovae. We found that on average SN Ic explosion sites are
more metal-rich and younger than SN Ib sites. The initial mass of the progenitors derived from parent
stellar population age suggests that SN Ic have more massive progenitors than SN Ib. In addition,
we also found indication that some of our SN progenitors are less massive than ∼ 25 M⊙ , indicatingthat they may have been stars in a close binary system that have lost their outer envelope via binaryinteractions to produce Ib/c supernovae, instead of single Wolf-Rayet stars. These findings support
the current suggestions that both binary and single progenitor channels are in effect in producing typeIb/c supernovae. This work also demonstrates the power of integral field spectroscopy in investigatingsupernova environments and active star forming regions.

2

Kuncarayakti et al.
Subject headings: supernovae: general — stars: massive
1. INTRODUCTION

A great number of supernovae (SNe) have been observed and new ones are being discovered owing to ongoing transient surveys and monitorings. Despite the large,
growing number of observed events the real nature of theprogenitor of each type of supernova is still not very wellunderstood.
Recently, a number of core-collapse supernovae (CCSNe) have had their progenitor star detected in high resolution pre-explosion images (e.g. Van Dyk et al. (2012);
Fraser et al. (2011); Elias-Rosa et al. (2011); see Smartt(2009) for a review). The detection of the progenitor
in several passbands allows the comparison between observed colors and luminosity of the star with stellar models. While direct detection is obviously desirable, in mostcases only upper luminosity limits could be derived due
to non-detection. This, however, is still useful in constraining the progenitor properties. Comparison withtheoretical models yields the evolutionary stage and position in the Hertzprung-Russel diagram of the star, fromwhich the initial mass could ultimately be derived. Using
this method Smartt et al. (2009) concludes that SNe II-P
arise from red supergiant stars with initial mass between
8.5+1−1.5 and 16.5 ± 1.5 M⊙ .
While the progenitors of SNe II-P have been convincingly detected and characterized, currently no Ib/c progenitor has been detected. It is widely believed that since
SNe Ib/c are deficient in hydrogen and helium, the most
likely candidate for their progenitors would naturally be
the Wolf-Rayet (WR) stars (Crowther 2007). Numerous stellar evolution models have been proposed to characterize the progenitor stars of different SN types (e.g.
Heger et al. 2003; Eldridge & Tout 2004; Georgy et al.
2009) but these predictions are still not very well tested
with observational data. Progenitor discoveries could
provide useful comparisons but the number of data points
is still too small and not very reliable, considering a number of uncertainties such as metallicity assumption andalso the sensitivity of the method to errors in luminosity (determined using host galaxy distance) and the end
state of the evolution of the exploding star. Furthermore,progenitor discoveries ideally should be followed-up by
post-explosion observation to ensure that the purported
progenitor has indeed gone. However, this has not been
done for the majority of the progenitors thus future confirmation of their disappearance is still needed.
Initial mass of a progenitor star is generally consideredas the most influential parameter driving the evolutionof the star. Hydrogen-deficient (type-Ib, Ic) SNe require
progenitors with high mass-loss rate to remove the outerhydrogen envelope of the star, in which metallicity-driven
wind (e.g. Vink et al. 2001) or other mechanism could
play a significant role. Therefore, it is also important
to investigate the metallicity of the progenitor star in
addition to the initial mass. This dependence on metallicity affects the number ratio NIb/c /NII as suggested
by several previous studies (Prantzos & Boissier 2003;
hanindyo.kuncarayakti@ipmu.jp

Boissier & Prantzos 2009; Eldridge et al. 2008). Anotherpossible mechanism of mass loss is via close binary interaction (e.g. Podsiadlowski et al. 1992). Extending thework of Smartt et al. (2009) for SN Ib/c progenitors,
Eldridge et al. (2013) suggest that the non-detection of
SN Ib/c progenitors may be explained by the idea thatprobably most of SN Ib/c progenitors arise from interacting binaries with mass . 20 M⊙ . An example
where binary scenario provides a good alternative explanation to the massive single star progenitor is given by
Crockett et al. (2007) in the case of SN Ic 2002ap. From
analysis of pre-explosion images, they suggest that theprogenitor of SN 2002ap was probably initially a 30–40
M⊙ star with twice the standard mass-loss rate, or in abinary system as a 15–20 M⊙ star.
Anderson et al. (2010) showed that SNe Ib/c occur inhigher metallicity environments than SNe II. High metallicity massive stars tend to explode as SNe Ib/c, thus
higher number ratio NIb/c /NII is expected in highermetallicity environment. While Anderson et al. (2010)
suggest that SN Ib and Ic have similar metallicities,
Modjaz et al. (2011) argue that SN Ic have higher metallicity than Ib. The results of Leloudas et al. (2011), andrecently Sanders et al. (2012), also show indications forhigher metallicity for Ic, but those were not statisticallysignificant. In contrast with this work, all those previous
studies mentioned above used slit spectroscopy to obtain
spectra of the SN explosion sites, from which the site
metallicities were derived.
Considering the limitations of finding SN progenitors
in high-quality pre-explosion images, several alternative
methods have been devised to obtain insights into thenature and possible mass range of the progenitors. A
statistical study by Anderson & James (2008) using correlations of SN positions within host galaxies with Hαemission showed that the association of SNe with recent
star formation follows a SN Ic > Ib > II sequence, indicating a grouping of decreasing progenitor mass. This
result is further reinforced in Anderson et al. (2012); but
see Crowther (2013) for a discussion on how SN association with a nearby HII only constrains the progenitor
mass weakly. Leloudas et al. (2011) suggest that SN Ib/cprogenitors are more massive than 25–30 M⊙ from theage of the youngest stellar population at the explosion
site, estimated using Hα emission line equivalent width.
However, in that case it is likely that multiple stellar
populations have been observed and treated as a single
one since the study used integrated light over a large
region within the spectrograph slit, in some cases ∼ 1
kpc. Some of their targets are also not the exact explosion sites but other regions several kpc away in the hostgalaxy. Therefore, consequently the real parent population might has been contaminated by other populationsof possibly different ages and metallicities. This problem
is also present in similar studies such as Modjaz et al.
(2011) and Sanders et al. (2012). Here we endeavour
to refine the results of those efforts by resolved spectroscopy of the explosion site, with typical spatial resolution of around 70 pc (1” at 15 Mpc). A similar approachhas been employed by Gogarten et al. (2009) to estimate

SN site IFU spectroscopy – Ib/c progenitors
the initial mass of the progenitor of the optical transient
NGC 300 OT2008-1. They probed region ∼50 pc aroundthe transient, and determined the initial progenitor massof 12–25 M⊙ from the analysis of the stellar population
at the site.
In this paper we report the results of our study of
11 nearby Ib/c SN explosion sites, in which the parent stellar populations were detected and used to derive progenitor star’s mass and metallicity. We will use
the terms star cluster, HII region, and OB associationinterchangeably in this paper to refer to the stellar population. As stars are born in clusters (Lada & Lada
2003, also see Bressert et al. (2010) who suggest that
this depends on the adopted cluster definition, which
may change the fraction of stars born in clusters tobe ∼ 45–90%) and there is evidence that all massive stars may be born within clustered environments(Portegies Zwart et al. 2010), it is reasonable to derivea coeval star’s age and metallicity from its parent stellar population. It is not expected that the progenitor
star would have wandered far from the birthplace cluster since they would not have much time to travel before
exploding as a supernova – thus the parent cluster may
be studied to extract useful information on the coeval
SN progenitor star. Typical velocity dispersion inside
a star cluster is a few km/s (Bastian & Goodwin 2006;
Portegies Zwart et al. 2010), which corresponds to abouta few pc/Myr. Therefore a SN progenitor which belongs
to such cluster, if unbound, would only travel typicallya few tens of parsec during its several Myr lifetime. By
studying the host cluster we were able to derive initial
mass and metallicity of the SN progenitors.
We organize the paper as follows. Observation, data
reductions, and the subsequent analysis is presented in
Section 2. Descriptions of each SN explosion sites are
given in Section 3. We discuss our findings in Section 4
and finally a summary is presented in Section 5.
2. DATA ACQUISITION AND ANALYSIS METHOD

We selected our samples from the Asiago Supernova
Database (Barbon et al. 1999). SNe in host galaxies
with radial velocity of 3000 km/s or less were selected
and subsequently careful visual inspections were performed to DSS and SDSS images of the explosion sites
using ALADIN1 . We use equatorial coordinates from the
Asiago database to locate the SN positions in the images. In addition, we also used the published imagesof the SN environment/light echo study by Boffi et al.
(1999) to compare with and identify some SN host clusters. SN classification follows the Asiago database classification; in this paper we present the study of ourSNe Ib/c samples while the type-II SNe are presented
in Kuncarayakti et al. (2013, Paper II).
SNe showing close association with a bright knot wereselected as observation targets. We interpret these knots
as the parent stellar population of the SN progenitor star.
The utilization of broadband images ensure that there isno selection preference towards very young stellar populations, as opposed to if we carried out our selection
using Hα or UV images. Therefore, we expect very little
age bias to be present in our sample explosion site.
1 http://aladin.u-strasbg.fr/aladin.gml

3

We observed 7 of our targets in 2010-2011 using
the SuperNova Integral Field Spectrograph (SNIFS;
Aldering et al. (2002), Lantz et al. (2004)) mounted at
University of Hawaii 2.2 m telescope (UH88) at Mauna
Kea. Table 1 contains the observations of our SN sitetargets. The positional uncertainty of each SN is also
showed; the reasons for each estimates are given in thedescription of each explosion sites.
The integral field spectrograph SNIFS employs a fullyfilled 15 × 15 lenslet array in the integral field unit (IFU),
covering 6.4”×6.4” wide field of view (FoV). The corresponding spatial resolution is 0.43 arcsec per spatial
pixel (spaxel). SNIFS has a photometric channel thatis used to accurately place objects in the IFU. The positional accuracy with which a given (RA, Dec) coordinates is placed on the IFU is around 0.2 arcsec. The
scale and rotation of the SNIFS IFU is well measured
thus should not produce much additional astrometric uncertainty. The spectrograph consists of two arms operating simultaneously to cover the whole optical wavelength range at R ∼ 1000: the blue channel covers
3300 – 5200 Å and the red channel covers 5100 – 9700
Å. SNIFS is operated remotely with a fully-dedicateddata reduction pipeline. The final pipeline result iswavelength- and flux-calibrated (x, y, λ) datacubes. The
description of the pipeline is similar to what is presented
in §4 of Bacon et al. (2001) and is outlined briefly in
Aldering et al. (2006).
Observation of the other 4 targets was carried out
using the Gemini Multi-Object Spectrograph (GMOS)
in IFU mode (Allington-Smith et al. 2002; Hook et al.
2004), with the 8.1 m Gemini North telescope at Mauna
Kea (Program ID GN-2011B-C-6, via Subaru–Gemini
Time Exchange Program). GMOS was used in one-slit
mode, providing a 5” × 3.5” field of view sampled by
the hexagonal lenslet array with one lenslet diameter of0.2”. We used the B600 grating centered at 5400 Å, andalso took identical exposures with the grating centeredat 5450 Å in order to perform spectral dithering to eliminate cosmic rays and cover the gaps of the three CCDs
utilized by GMOS. This enables us to observe continuous spectra from 4000 Å to 6800 Å at R ∼ 1700, thus
covering and resolving prominent spectral lines such as
Hα, Hβ, Hγ, Hδ, [OIII]λλ4959,5007, [NII]λλ6548,6583,
and [SII]λλ6716,6731. Subsequent data reduction was
carried out using the Gemini package in IRAF2 . The
data was reduced to remove instrumental signatures andthen calibrated in wavelength and flux to produce final(x, y, λ) datacubes.
Once the raw SNIFS and GMOS data have been fully
reduced into (x, y, λ) datacubes, object spectrum extraction and analysis were done using IRAF. The datacubes
were treated as stacks of images taken at different wavelengths. The flux density of an object at each wavelength’slice’ was extracted by performing aperture photometry(IRAF/apphot ) on the object at each slice, and arranging the values in the wavelength direction to produce aspectrum. The seeing FWHM was used as the radius of
the circular aperture, or in some cases smaller apertures
2 IRAF is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities
for Research in Astronomy, Inc., under cooperative agreement with
the National Science Foundation.

4

Kuncarayakti et al.

were used due to object proximity to the edge of the
field of view. Sky in SNIFS data was estimated using anannular aperture around the object and subtracted out.
Usually the annulus is larger than the field width thus
effectively only a part of it was being used to measure thesky. GMOS is equipped by another IFU dedicated for simultaneous sky observation during the science exposures,and subtraction was done in the reduction process.
The positions of the objects in each SNIFS wavelength slice were traced, thus compensating the differential atmospheric refraction effect (DAR; Filippenko
1982). This demonstrates the advantage of using integral field spectroscopy (IFS) compared to conventionalslit spectroscopy which is strongly affected by DAR, andwith IFS the effects of DAR could be corrected a posteriori as has been shown by Arribas et al. (1999). The
GMOS dataset was corrected for DAR in the datacube
stage by shifting each wavelength slices, and aperture
photometry of individual slices was done with fixed aperture position for each object.
The final resulting spectra were then analysed using
IRAF/splot. Nebular emission lines were measured byfitting a Gaussian profile. To measure metallicity, only
the nebular emission lines are needed thus the stellar continuum was removed prior to line measurement by fittinga polynomial function. Before measuring line equivalent width, the continuum was normalized also by fitting with a polynomial. Metallicity in terms of oxygen
abundance was derived using the O3N2 and N2 calibrations by Pettini & Pagel (2004, hereafter PP04). Thismethod of metallicity determination uses intensity ratiosof lines closely spaced in wavelength, therefore not sensitive against errors introduced by reddening and flux
calibration.
Following PP04, we adopt 12 + log (O/H) = 8.66 as
the value of the solar oxygen abundance (Asplund et al.
2004). In all of the observed fields Hα and [NII]λ6583
were detected thus enabling N2 determination, while theHβ and [OIII]λ5007 detection required for O3N2 is lessfrequent. In cases where both O3N2 and N2 were detected we adopt the mean value as the metallicity, otherwise the N2 value is adopted. The errors quoted in metallicity in Z⊙ unit are the bounds for the highest and lowest
values of 12+log(O/H) determined from O3N2 and N2.
In cases where only N2 is available, we assign the error of
12+log(O/H) as ±0.18 dex, which is the 1σ uncertainty
in the PP04’s N2 calibration determination. These werethen converted into Z⊙ metallicities to give the highest
and lowest value bounds of metallicity.
Ages of the stellar populations were determined bycomparing the observed Hα equivalent width (EW)with the theoretical values provided by simple stellar population (SSP) model Starburst99 (Leitherer et al.
1999) for each appropriate metallicity. We assume an
instantaneous-burst stellar population with continuous,standard Salpeter IMF (α = 2.35). The evolution of
HαEW with SSP age is presented in Figure 1. HαEW
of a stellar population with continuous star formation is
also shown for comparison. The evolution of Hα is sensitive to the star formation history, while IMF variations
give less important effect especially at SSP age older than
∼ 4 Myr. The error of HαEW were estimated from thesignal-to-noise ratio of the spectral continuum around
Hα. We expect the effect of dust absorption in HαEWFigure 1. Time evolution of Hα equivalent width, Starburst99
SSP. Single-burst model is represented with black line color andcontinuous star formation with purple; both use standard Salpeter
IMF with α = 2.35, Mup = 100 M⊙ . Dotted lines represent singleburst solar-metallicity models with different IMFs: red is for α =3.30, Mup = 100 M⊙ , orange is for α = 2.35, Mup = 30 M⊙ . The
lifetimes of single stars of different initial masses at solar metallicity
according to Padova models are indicated with vertical grey lines.

determination to be minimal due to the very small wavelength range used for EW measurement. The SSP age determined from HαEW is adopted as the lifetime of the coeval progenitor star, and comparison with Padova stellar
evolution models gives the estimated initial mass of a starwith such lifetime. We used models from Bressan et al.
(1993) for solar metallicity (Z = 0.02), and Fagotto et al.
(1994) for 0.4 solar metallicity (Z = 0.008). We definedobserved oxygen abundance of 0.7 (O/H)⊙ , corresponding to 12+log(O/H) = 8.50, as the dividing line between
using the solar-metallicity model or the subsolar one todetermine stellar initial mass. These models extend fromthe zero-age main sequence (ZAMS) to the onset of central carbon burning. This is considered representative of
the stellar lifetime since the time elapsed from carbon
burning to SN is only about a few hundred years, negligible compared to the ∼ 106 − 107 year lifetime of thestar.
We compare Starburst99 model of HαEW against
GALEV(Anders & Fritze-v. Alvensleben
2003;
Kotulla et al. 2009), to check for consistency andpossible systematic effects. Both SSP models consider
the contribution of stellar and nebular continuum tothe output light, but GALEV includes nebular line
emissions. As for the HαEW value as a function of SSPage, Starburst99 provides the tabulation of the values
while GALEV does not. Therefore, individual spectraof GALEV SSP models of different ages were extracted
and then Hα equivalent widths were measured using
IRAF/splot with the same procedure as the one applied
to observational data. The result comparing the twodifferent SSP models is presented in Figure 2. For both
Starburst99 and GALEV we assume an instantaneous
burst of a stellar population with Salpeter IMF at solar
metallicity, using Geneva stellar library. From the plot it
is evident that HαEW may differ by a factor two or more
between the two models. We attribute this difference
partly because of the resolution difference of the model
SED. GALEV SEDs have resolution of 20 Å at Hα,thus the neighboring nitrogen lines ([NII]λλ6548,6583)
were not resolved thus contaminated the Hα in the EW
measurement. However, this EW difference translates

SN site IFU spectroscopy – Ib/c progenitors

5

Table 1
Target SN sites IFU observations
SN

Type

RA2000Dec2000

σα,δ

Galaxy (NSN )d/MpcaObs. dateb

Inst.cExposure

Seeing

1964L
1994I
2000ew
2004gt2007gr2009em
1983N
1984L
1999ec2008bo2009jf

Ic
Ic
Ic
Ic
Ic
Ic
Ib
Ib
Ib
Ib
Ib

11:52:49.09
13:29:54.07
11:40:58.52
12:01:50.37
02:43:27.98
00:34:44.53
13:36:51.23
02:35:30.54
06:16:16.16
18:19:54.41
23:04:52.98+44:07:45.4+47:11:30.5+11:27:55.9−18:52:12.7+37:20:44.7−08:23:57.6−29:54:01.7−07:09:30.3−21:22:09.8+74:34:21.0+12:19:59.5

±2”
±1”
±0.7”
±0.005”±0.02”
±1”
±0.6”
±0.3”
±0.2”
±0.2”
±0.06”NGC 3938 (3)NGC 5194 (4)NGC 3810 (2)NGC 4038 (4)NGC 1058 (3)NGC 157 (1)NGC 5236 (5)NGC 991 (1)NGC 2207 (4)NGC 6643 (2)NGC 7479 (2)

17.4
7.9
17.8
20.9
7.7
19.5
6.9
18.8
31.3
22.1
33.9

2011 Mar 13
2011 Mar 102011 Mar 15
2011 Mar 102011 Sep 29
2011 Sep 29
2011 Mar 11
2011 Sep 29
2011 Mar 10d
2010 Aug 1
2011 Sep 29

S
S
S
S
G
G
S
G
S
S
G

1800 s ×2
1800 s ×2
1800 s ×2
1800 s ×2
1800 s ×4
1800 s ×2
1800 s ×1
2700 s ×2
1800 s ×2
1800 s ×1
1800 s ×4

0.8”
1.1”
0.9”
1.2”
0.5”
0.6”
1.5”
0.6”
1.1”
0.8”
0.5”

a Mean redshift-independent distance from NED (http://ned.ipac.caltech.edu).
b Hawaiian Standard Time (UTC – 10).
c Instrument used: S = SNIFS, G = GMOS.
d Great East Japan Earthquake occurred during the exposure of this object; observation was conducted remotely from Tokyo but fortunately

the earthquake did not introduce any effect to the observation and data.

emission lines, typical of a young stellar population. Figure 3 shows the appearances of the explosion site on the
IFU focal plane and the extracted spectrum of the hostcluster. The measured metallicity is 1.09 solar. Measurement of Hα equivalent width shows that the cluster
is very young, with derived age of 3.3 Myr. The corresponding stellar initial mass of that age at solar metallicity is about 120 M⊙ .
2. SN 1994I site
Figure 2. Comparison of Hα equivalent width evolution fromdifferent SSP models, Starburst99 and GALEV.

into only a small difference in age, in the order of
1–2 Myr. This, eventually, will lead into difference oftypically only about 20–30 % or lower in star initialmass, depending on the region of the age probed by
Hα equivalent width. Therefore, we conclude that the
selection of SSP model does not introduce significant
sytematics to the final result of progenitor star initialmass. In this case, Starburst99 was preferred over
GALEV since it has better temporal resolution.
3. THE EXPLOSION SITES
3.1. SNe Ic sites

1. SN 1964L site
SN 1964L exploded in NGC 3938, a spiral galaxy hosting two other SNe (type II SNe 1961U and 2005ay – seePaper II). This SN is poorly studied and no reference
discussing the nature of the progenitor of this particular object was found in the literature. Blaylock et al.
(2000) recovered the photographic spectra of the SN andclassified it as type-Ic. We found that the cited position of SN 1964L is within 3 arcsec of a bright clusterin the host galaxy. Based on the measurements of the
Palomar survey plates, the position was shown to be accurate to within 2” by Porter (1993). SNIFS data showsthat this source exhibits a blue continuum with strong

SN 1994I is one of the best-studied type-Ic SNe due to its
location in M51, a very well-observed nearby galaxy. It
has often been referred as the ’standard’ SN Ic although
it also exhibited unusual behaviour (e.g. Sauer et al.
2006). Nomoto et al. (1994) suggests that the progenitor of this SN is a 4.0 M⊙ helium star in a binary system rather than a single WR star, which later evolved
into a C+O star and eventually produced a SN Ic explosion. The main sequence initial mass of this star was
estimated as 15 M⊙ . The position of this SN is accurate
within 1”, as estimated by van Dyk (1992) for SNe ofthat era, and later confirmed by the late-time observations of Clocchiatti et al. (2008).
Our SNIFS result shows that the explosion site israther diffuse, the host cluster does not stand out prominently over the stellar background (Figure 4). The extracted spectrum shows faint continuum and a weak Hαline. Metallicity was derived to be 0.83 solar from N2 –this SN is the only SN Ic without an O3N2 determination in our sample since the lines Hβ and [OIII]λ5007
are not detected. The Hα equivalent width corresponds
to an age of 11.0 Myr. This age at solar metallicity corresponds to the lifetime of a 17.9 M⊙ star, which is too
low for a single WR progenitor but quite consistent withthe binary model of Nomoto et al. (1994). This is possibly one of the first strong pieces of evidence of a binary
progenitor channel in SN Ic production.
3. SN 2000ew site
SN 2000ew exploded in NGC 3810 and is the first
SN Ic with detected emission of near-infrared carbon

6

Kuncarayakti et al.

Figure 3. Left panel: SN 1964L site reconstructed IFU FoV. SN position within 1 arcsec error radius is indicated by a circle. Approximate
linear scale corresponding to 2 arcsec is also indicated; this scale is calculated from the host galaxy distance only thus does not take into
account the projection effect and host galaxy inclination. ”SC” indicates the host star cluster. Right panel: extracted spectrum of the starcluster.

Figure 4. IFU FoV and extracted host cluster spectrum for the SN 1994I site. The red end of the spectrum is truncated due to DAR.
Figure annotations are the same as in Figure 3.

monoxide (CO) in the spectrum (Gerardy et al. 2002).
Van Dyk et al. (2003) searched the progenitor star in the
pre-explosion images but found none within their detection limit. Comparing with HST images taken while the
SN is still visible, the derived SN position is accurate
to within 0.7”. However, they discovered that luminous
blue-yellow stars are present in the explosion site, within
1 arcsec of the SN position. The color-magnitude diagram suggests that the environment is very young, . 6
Myr old. Similarly, Maund & Smartt (2005) also failed
to detect the progenitor star in pre-explosion images andderived an age estimate of the environment within 6
arcsec from the SN of ∼ 7 Myr, assuming twice solar
metallicity. Maund & Smartt (2005) estimated progenitor mass between 12 and 40 M⊙ from the environmentage.
Our SNIFS result shows that the cluster coincident
with SN position, indicated as SC-B in Figure 5, is indeed very young with age of 5.8 Myr. This is consistent
with the estimate of Van Dyk et al. (2003). The brighter
neighbouring cluster, SC-A, is slightly older, 6.3 Myr.
Both clusters have similar metallicities of 1.15 and 1.05
solar, respectively. This on-site metallicity measurement
is definitely more reliable compared to the twice-solar
metallicity assumed in the previous studies. The corresponding main sequence initial mass for a 5.8 Myr stellar population at solar metallicity is 33.9 M⊙ , while it is29.5 M⊙ for the 6.3 Myr population.
4. SN 2004gt site
Gal-Yam et al. (2005), and also Maund et al. (2005) reported their efforts in recovering the pre-explosion progenitor of SN 2004gt in the Antennae Galaxy, NGC 4038.
However, the detection results were negative and only upper luminosity limits could be derived for the progenitor
star (positional uncertainty 5 mas). Both investigations

could not rule out a massive Wolf-Rayet star progenitor,
and also allow binary interaction scenario for producing
the stripped-envelope progenitor star. The positional uncertainty of the SN in the HST images was estimated to
be around 5 mas.
Our result with SNIFS shows that SN 2004gt exploded
in a large star cluster complex (Figure 6), identified
as Knot S by Whitmore et al. (2010). We derived themetallicity of Knot S as 12+log(O/H) = 8.71, or 1.12 solar, with age of 5.78 Myr. This result is consistent with
Knot S mean age estimate by Whitmore et al. (2010) of
5.75 Myr. The age of 5.78 Myr corresponds to the lifetime of a star with initial mass of 33.7 M⊙ at solar metallicity. We also detect WR star feature in the spectra at
4650 Å. A metallicity determination of the explosion site
by Modjaz et al. (2011) gave 12+log(O/H) = 8.70+0.00−0.01 ,
using the PP04 O3N2 scale. Our O3N2 determination
yields a higher value, 12+log(O/H) = 8.78. The difference may have come from the different regions being
observed, due to the different spectroscopy techniques(slit vs. IFU). However, if the uncertainty in the PP04
O3N2 calibration of 0.14 dex is considered as the errors
for both determinations, this difference is statistically insignificant, corresponding to only 0.4σ.
5. SN 2007gr site
We used GMOS to observe the explosion site of
SN 2007gr which exploded in the galaxy NGC 1058.
Hunter et al. (2009) reported an extensive observationof the SN at optical and infrared wavelengths, covering
more than 400 days. They showed that the photometricevolution of SN 2007gr is similar to SN 2002ap, an energetic Ic hypernova, but the spectra of the two SNe show
marked differences. Tanaka et al. (2008) performed spectropolarimetric observation of the SN and suggested thata bipolar explosion viewed slightly off-axis may best rep-SN site IFU spectroscopy – Ib/c progenitors

7

Figure 5. IFU FoV and extracted cluster spectra for the SN 2000ew site. Figure annotations are the same as in Figure 3.

Figure 6. IFU FoV and extracted host cluster spectrum for the SN 2004gt site. Figure annotations are the same as in Figure 3.

resent the explosion model of SN 2007gr. A study using
pre-explosion imaging data by Crockett et al. (2008a) reported that the SN exploded very near (∼ 7 pc) a pointlike source in HST images, which they proposed as thecompact host star cluster of the SN progenitor star. The
positional uncertainty of the SN is about 0.02”. Their determination of the compact cluster age using broadband
photometry gives two solutions: 7 and 20–30 Myr assuming solar metallicity, corresponding to turnoff masses of
28 and 12–9 M⊙ , respectively.
GMOS observation of the explosion site was seeinglimited at 0.5”. Despite the excellent seeing condition,
the compact clusters and bright individual stars comprising the OB association resolved in HST images could not
be resolved and they appear collectively as bright knots
in the IFU reconstructed images. We extracted the spectra of each of these five sources, designated SC-A through
SC-E, including the central association where SN 2007gr
exploded (SC-A). We derived the metallicity of SC-A as
1.12 solar, with age of 7.8 Myr, quite consistent withthe 7 Myr solution of Crockett et al. (2008a). This age
corresponds to the lifetime of a 24.4 M⊙ star at solar
metallicity. Modjaz et al. (2011) measured the metallicity at the explosion site to be 12 + log(O/H) = 8.64+0.07−0.09
in PP04 O3N2 scale. Our O3N2 determination yields 12+ log(O/H) = 8.69, which is different with Modjaz et al.
(2011)’s result only by 0.25σ – this is not significantly
different.
Compared to other surrounding knots, SC-A appears
to be older by about 1 Myr. All other knots SC-B
through SC-E have ages between 6.4 and 6.8 Myr, which
may suggest triggered star formation propagating insideout from SC-A. If star formation in the outer clusters
was triggered from SC-A, then the 1 Myr time differenceand ∼ 50 pc projected distance would correspond to a
projected propagation velocity of ∼ 50 km/s. The Hαmap of the region shows shell-like structure surrounding
SC-A and coincident with the other four knots, leaving
a depression in Hα intensity at the position of SC-A –further reinforcing this scenario. In any case, the agesof the other four knots corresponds very well with the
lifetimes of massive stars, around 28–29 M⊙ . Interestingly, SC-E shows relatively lower, sub-solar metallicity(0.85 Z⊙ ) compared to other knots present at the site,which are super-solar (> 1.1 Z ⊙ ).
6. SN 2009em site
The Ic SN 2009em is not well studied, discovered by
Monard (2009) about 2 months after maximum light asconfirmed by Navasardyan & Benetti (2009) and also by
Folatelli & Morrell (2009). The spectrum matches normal type Ic events. There is no other information on
this object available in the literature. We assign positional uncertainty of the SN as 1”, considering that it
is a modern SN. The host galaxy NGC 157 is a granddesign Sc spiral, harbouring no other SN to date except
2009em.
With GMOS we observed the explosion site and detect two clusters. The more prominent cluster, SC-A,
exhibits sub-solar metallicity of 0.76 Z⊙ , with age of 6.8
Myr. The neighbouring fainter cluster SC-B is barely
detected in continuum images but stands out in Hα. It
has nearly twice the metallicity of SC-A, 1.45 solar. The
age of this cluster was derived as 6.3 Myr. The significant difference of the two clusters’ metallicities illustrates
the importance of measuring the metallicity of explosion
sites with fine spatial resolution. The SN itself exploded
at about the same distance from both clusters, but we assigned SC-A as the host cluster since it is the brighter one
and thus more likely to host more progenitor candidates.
The ages of the clusters correspond to the lifetimes of
27.7 and 29.5 M⊙ stars, for SC-A and SC-B respectively.
3.2. SNe Ib sites

1. SN 1983N site
SN 1983N exploded in a nearby large spiral galaxy, M83(NGC 5236). This SN was observed extensively (e.g.

8

Kuncarayakti et al.

Figure 7. IFU FoV and extracted cluster spectra for the SN 2007gr site. The continuum image of the GMOS FoV was made by collapsing
the datacube in wavelength direction, approximately covering the V -band. Figure annotations are the same as in Figure 3.

Figure 8. IFU FoV and extracted cluster spectra for the SN 2009em site. Figure annotations are the same as in Figure 3.

Table 2
Results for SN Ic sites
SN site
1964L
1994I
2000ew
2000ew
2004gt2007gr2007gr2007gr2007gr2007gr2009em2009emObject
SC*
SC*
SC-A
SC-B*
SC*
SC-A*
SC-B
SC-C
SC-D
SC-E
SC-A*
SC-B

Offset/”(pc)a2.6 (220)
2.6 (110)
2.3 (220)
1.2 (110)
1.3 (140)
0.0 (0)1.4 (52)
1.1 (41)
1.6 (59)
1.0 (37)
1.1 (100)
1.0 (94)(O3N2)
8.83
–
8.77
8.85
8.78
8.69
8.96
8.82
8.99
8.65
8.57
8.85

(N2)

12+log(O/H)

Z/Z⊙

8.70
8.58
8.68
8.72
8.71
8.71
8.80
8.75
8.79
8.60
8.54
8.82

1.09+0.39−0.27
0.83+0.43−0.28
1.05+0.23−0.22
1.15+0.40−0.30
1.12+0.20−0.17
1.12+0.03−0.05
1.35+0.64−0.42
1.20+0.25−0.20
1.35+0.79−0.52
0.85−0.14−0.09
0.76+0.05−0.05
1.45+0.10
−0.13

8.57
8.58
8.58
8.59
8.64
8.72
8.63
8.68
8.58
8.54
8.51
8.78

HαEW/Å

Age/Myr

M/M⊙

939.10 ± 84.52
13.34 ± 1.87
68.18 ± 8.18
221.10 ± 35.38
209.60 ± 10.48
15.57 ± 0.96
33.03 ± 3.30
59.62 ± 2.47
50.26 ± 5.03
27.95 ± 1.39
26.88 ± 2.69
68.76 ± 5.09

3.28+0.04−0.04
11.0+0.25−0.75
6.31+0.04−0.04
5.75+0.09−0.09
5.78+0.03−0.03
7.84+0.75−0.25
6.66+0.06−0.05
6.36+0.01−0.02
6.42+0.06−0.04
6.78+0.08−0.05
6.84+0.30−0.09
6.31+0.02−0.03

120−10+1
17.9−0.4+0.8
29.5−0.2+0.1
33.9−0.8+1.0
33.7−0.3+0.2
24.4−2.5+0.8
28.3−0.2+0.1
29.3−0.1+0.1
29.1−0.2+0.1
27.9−0.3+0.2
27.7−1.0+0.4
29.5−0.1+0.1

a Offset between SN and approximate cluster center.
* SN parent cluster.

Gaskell et al. 1986; Weiler et al. 1986; Clocchiatti et al.
1996) and has been suggested to be the prototypical typeIb SNe along with SN 1984L (Porter & Filippenko 1987).
Sramek et al. (1984) reported the first radio detection ofa type I SN of this SN 1983N. Clocchiatti et al. (1996)
reported that their astrometry of the SN position is accurate to within ∼ 0.6”.
Using SNIFS we discovered that the explosion site of
the SN is quite complex, with three detected objects
within the IFU FoV. In the continuum a prominent clus-

ter was detected, but this cluster is overshadowed in Hα
by two bright nearby HII regions (see Figure 9). We
extracted the spectra of SC-A cluster and the HII region north-east of it (SC-B), but failed to do so for the
HII region south-east of the cluster since it is situated at
the edge of the FoV. It is likely that this third cluster issimilar in age with SC-B considering its detectability inHα and nondetection in continuum images. The cluster
SC-A was found to be 7.2 Myr old with 1.02 times solar
metallicity while the HII region SC-B has age of 2.6 Myr

SN site IFU spectroscopy – Ib/c progenitorswith 0.89 solar metallicity. The age of SC-A corresponds
to the lifetime of a 26.4 M⊙ star while the SC-B age isconsidered too young to even produce a supernova.
2. SN 1984L site
SN 1984L exploded in NGC 991, a low surface brightness spiral galaxy. Schlegel & Kirshner (1989) presented
late-time photometry and spectroscopy of the SN, andsuggested that it originated from a roughly 20 M⊙ star.
Later, Swartz & Wheeler (1991) derived an ejecta massof more than 10 M⊙ , which they inferred to be the resultof an explosion of a & 30 M⊙ star. Baron et al. (1993)
put forward the problem in reconciling the early-timelight curve with the spectra of the SN, for which they proposed a solution by suggesting the scenario in which explosion of a very massive star (∼ 50 M⊙ of helium with 2
×1052 erg kinetic energy) produced a massive black hole.
The coordinates given by Schlegel & Kirshner (1989) differ by about 0.3” compared to those of Weiler et al.
(1986). This value is used as the positional uncertainty
of SN 1984L.
Our GMOS observation of the explosion site showsthat the host star cluster of SN 1984L does not exhibit
strong emission lines in its spectrum, indicating intermediate age. We measured the metallicity to be 0.45 solar,
the lowest in our sample. Hα emission equivalent widthis small, giving an age estimate of 18.0 Myr, which corresponds to the lifetime of a 13.5 M⊙ star. This result isinconsistent with previous studies suggesting a high-mass(& 20 M⊙ ) progenitor, but intriguing since the derived
mass of 13.5 M⊙ lies well below the currently accepted
WR star mass limit and within the range of SN II-P
progenitors. With such low metallicity, it is even moredifficult to remove the hydrogen envelope of a single star
via stellar wind mechanism, and as a result the minimum
mass of a star to become a WR star increases. Thus, thisis a strong indication that the SN 1984L progenitor may
have lost its envelope in a close binary system.
3. SN 1999ec site
The Ib SN 1999ec exploded in the interacting spiralgalaxy, NGC 2207. Currently there have been four
recorded SNe that have occurred in this galaxy (SNe1975A, 1999ec, 2003H, 2013ai). Van Dyk et al. (2003)
searched for the progenitor star in pre-explosion images
but found no convincing candidate. Their HST images
show that the SN occurred in an environment of blue,
apparently young stars and clusters. The SN position
uncertainty was ±0.2”.
With SNIFS we detect two large clusters in the SN
vicinity (Figure 11). Both clusters have similar spectra
and are of similar metallicity, with SC-A being 0.71 solar
value and SC-B of 0.74 solar. Also in derived age, bothshow similarity, with SC-A being 5.3 Myr and SC-B being 5.1 Myr. These age estimates at solar metallicity
correspond to the lifetimes of 38.0 and 41.6 M⊙ stars,
respectively. The derived initial mass is high, even compared to the majority of SN Ic progenitors.
4. SN 2008bo site

9

SN 2008bo exploded in a spiral host, NGC 6643. This
SN has been detected in X-ray (Immler et al. 2008;
Immler & Brown 2008) and radio (Stockdale et al. 2008)
wavelengths. The Asiago database assigned the type Ib
for this SN; Navasardyan et al. (2008) reported that the
spectrum shows the characteristics of a stripped-envelope
event but with deep Hα absorption. This resembles the
spectrum of SN 2008ax, a type IIb SN, which shows spectral evolution from type II to Ib. There is no other useful
discussion about the physical nature of the object in theliterature. Stockdale et al. (2008) reported that the radio position of this SN agrees well (∼ 0.2”) with theoptical position. Thus, we assign 0.2” as the positional
uncertainty of this SN.
We observed the explosion site using SNIFS and extracted the spectra of two clusters apparent at thesite (Figure 12). A prominent cluster, SC-A, appears
in all wavelengths while in Hα we detect a faint secondary cluster, SC-B, and some other fainter structuresin the FoV. We performed additional imaging observation of the SN 2008bo site using OPTIC camera at UH88
(Howell & Tonry 2003) in 2011. However, the surrounding fainter structures are not visible in our broadband
images. From SNIFS data SC-A was found to be 13.5
Myr old with 1.20 solar metallicity. We only managed
to extract a part of the spectrum of SC-B but nevertheless recovered the Hα region and derived an age via its
equivalent width, which is 6.4 Myr. The metallicity of
SC-B is derived as 0.85 solar. The 13.5 Myr age corresponds to a star with initial mass of 14.9 M⊙, while 6.4
Myr corresponds to 29.3 M⊙ . The 14.9 M⊙ derived mass
is too small for a star to produce a WR star that may
later explode as a SN Ib, thus it is likely that SN 2008bo
also may have been produced by a progenitor in binary
system.
5. SN 2009jf site
SN 2009jf exploded in one of the two prominent spiral arms of the barred spiral galaxy NGC 7479. It wasan energetic slow-evolving SN, indicating massive ejecta.
Sahu et al. (2011) presented 9-months of optical photometry and spectroscopy monitoring of this SN and suggested the main sequence mass of the progenitor to be& 20–25 M⊙ estimated from the ejecta mass. Further,
Valenti et al. (2011) also reported their 1-year monitoring of SN 2009jf and similarly concluded that the progenitor mass range is within 25–30 M⊙ . Their positional
uncertainty of the SN is in the order of 0.06”.
We observed the explosion site of SN 2009jf using
GMOS, two years after the discovery. The continuum IFU reconstructed image shows only one prominent
source in the field (Figure 13), which are the blended
sources A+B in Valenti et al. (2011). We assigned thedesignation SC-A star cluster for this blended source.
Making use of the capability of IFU we reconstructed
Hα image of the field, and found that clumpy shell-likestructure of ionized gas is present around SC-A. We assigned identification SC-B, SC-C, and SC-D for theseclumps. We found that the metallicity of this complex is
below solar, with SC-A being 0.78 solar value and SC-B,
C, D within 0.63–0.81 solar. The N2 metallicity of SCA in 12+log(O/H) equals 8.55 dex, agrees exactly withthe explosion site metallicity estimate of Sanders et al.

10

Kuncarayakti et al.

Figure 9. IFU FoV and extracted cluster spectra for the SN 1983N site. Figure annotations are the same as in Figure 3. The blue partof SC-B spectrum could not be extracted since it fell outside the FoV due to differential atmospheric refraction.

Figure 10. IFU FoV and extracted host cluster spectrum for the SN 1984L site. Figure annotations are the same as in Figure 3.

Figure 11. IFU FoV and extracted cluster spectra for the SN 1999ec site. Figure annotations are the same as in Figure 3.

Figure 12. IFU FoV and extracted cluster spectra for the SN 2008bo site. Figure annotations are the same as in Figure 3. Only a partof SC-B spectrum could be recovered due to DAR effects.

(2012), using slit spectroscopy of 0.7” slit width. However, they do not mention about the aperture size forspectrum extraction nor the seeing size during the observation. Sanders et al. (2012) determined the age of the
explosion site from Hβ equivalent width to be 9.0 Myr.
The age of SC-A from our determination is quite old,
18.2 Myr which corresponds to the lifetime of a 12.4 M⊙
star. The surrounding clusters are significantly younger,
between 6.0 and 6.4 Myr. These morphological characteristics are similar with what we found at the SN
2007gr explosion site, where the central host cluster inthe complex is older than the surroundings thus suggesting inside-out star formation activity. This formation
scenario has been observed elsewhere (e.g. Adamo et al.

2012), thus suggesting that triggered star formation may
not be uncommon in star formation complexes. Assuming the outer clusters formation was triggered from SC-A,
the projected outward velocity of star formation propagation in this complex is ∼ 300 pc per 12 Myr, or around
25 km/s. This is about half the projected velocity we inferred for the SN 2007gr site.
If the progenitor of SN 2009jf indeed originated in SCA, this would be a third example after SN 1984L and SN
2008bo of low-mass SN progenitor produced by binary
channel. In contrast, the surrounding environment age
is consistent with the lifetime of stars with mass around
30 M⊙ . We note that the progenitor mass inferred fromSN properties is more consistent with the outer envi-

SN site IFU spectroscopy – Ib/c progenitorsronment age rather than the stellar association closest
with the SN position. Valenti et al. (2011) found thatthe color of their source A is consistent with a stellar
population containing stars with maximum stellar massof 8–25 M⊙ , while source B is redder thus presumably
older. This is not inconsistent with our findings whichyield progenitor mass of about 12 M⊙ . However, it ispossible that the star formation history in the immediate vicinity of SN 2009jf is not instantaneous, and theprogenitor star was born from a younger burst comparedto the dominant older surrounding population.
4. DISCUSSIONS

It is very important to determine the metallicity andage of the explosion sites of SNe Ib/c to characterize theirprogenitor stars. Metallicity-driven wind is one widely
accepted scenario to remove the star’s hydrogen envelope
and produce a stripped SN. Our results show that even at
the SN explosion site metallicity variations from place toplace may be present, thus emphasizing the importanceof measuring local metallicity directly with the highest
spatial resolution possible and discouraging metallicity
determinations using proxies. The results are presented
in Tables 3 and 2.
Averaging metallicities of all the 12 objects present at
each explosion sites, we found mean metallicity for the
sample of SN Ic sites as 1.11√± 0.22 (RMS; standard error of the mean/SEM = σ/ N = ±0.06) Z⊙ , while thisvalue is reduced to 1.01 ± 0.17 (SEM = ±0.08) Z⊙ if only
the SN parent clusters are considered. For the case of SN
Ib sites the mean metallicity value is 0.79 ± 0.20 (SEM
= ±0.06) Z⊙ , and 0.83 ± 0.29 (SEM = ±0.13) Z⊙ for
SN Ib host clusters only. Notwithstanding the somewhat
small number of samples (6 SN Ic sites, 12 clusters; 5 SN
Ib sites, 11 clusters), this immediately suggests that SNe
Ic are produced in higher metallicity environments thanSNe Ib. The statistical significance of the difference between SN Ic and Ib host clusters metallicities determinedby the t-test is 1.2σ, while it is 3.7σ if we consider thesite metallicities.
Modjaz et al. (2011) argued that SNe Ic and Ib explode in different metallicity environments with a difference of 0.2 dex in 12+log(O/H), with total number ofsample of N = 35. Their Kolmogorov-Smirnov (KS) test
p-value of the null hypothesis of both SN types camefrom the same population yields 1%. Converting backour solar-unit metallicity values of the host clusters into
12+log(O/H) scale, we found 0.08 dex difference between
SN Ic and Ib explosion sites. The KS test p-value for our
two samples is 59%, which could not rule out the possibility that both samples are from the same population –however this might not be very meaningful considering
the small number statistics. For comparison, other studies by Leloudas et al. (2011, N = 20) and Sanders et al.
(2012, N = 33) also suggest higher metallicity for Ic (albeit not statistically significant), while Anderson et al.
(2010) found no difference between Ib and Ic metallicities (N = 24). The sample of Sanders et al. (2012) was
drawn from untargeted SN surveys, thus is likely to beless biased towards massive, high-metallicity host galaxies compared to a sample drawn from targeted SN surveys. Our result (N = 11) of 1.2σ significance suggeststhat on average SNe Ic are the more metal rich compared11

to SNe Ib, but not statistically significant. Therefore, it
is more closer to the conclusion of Leloudas et al. (2011)
who also found suggestion that SNe Ic are more metalrich compared to SNe Ib, similarly by 0.08 dex.
We note one interesting fact that for SN Ic sites themetallicity derived from O3N2 index is almost always (10out of 11) higher than from N2 index (3.7σ significance),
while it is the opposite for SN Ib sites (2.7σ significance).
Consistently for both SN Ic and Ib sites the measured
metallicity is always higher for SN Ic sites in either O3N2
or N2 scales. The high O3N2 metallicity may be indicative of N/O enhancement (Pérez-Montero & Contini2009). This behavior has been observed in galaxies withhigh O3N2 metallicity as reported by Berg et al. (2011),
and interpreted as galaxies evolving past Wolf-Rayetgalaxy phase as WR stars may elevate the observed N/Oratio.
The age of the SN explosion site provides clue to thelikely mass of the progenitor star. We averaged the ageof all detected clusters in our SN sites and found that SN
Ic sites have younger mean age than SN Ib sites, 6.6 ± 1.7(SEM = ±0.5) Myr compared to 8.6 ± 5.3 (SEM = ±1.6)
Myr. This trend is also present when comparing the agesof the host clusters, with SN Ic hosts averaged 6.7 ± 2.6(SEM = ±1.1) Myr while for SN Ib hosts the age is significantly higher, 12.4 ± 5.9 (SEM = ±2.6) Myr. This
result shows that it is likely that SNe Ic resulted fromhigher-mass progenitors than SNe Ib (2.0σ significance).
Considering the results for individual objects, we alsosuggest that some SN Ib/c progenitors may have originated from close binary systems due to the derived old
age of the host cluster. SN 1994I is one example for
SN Ic with derived old parent cluster age, or low massprogenitor. The derived age of 10.9 Myr corresponds
to the lifetime of a 17.9 M⊙ single star, which is not
massive enough to evolve into a stripped-envelope WR
star thought necessary to produce SN Ic. Therefore, one
likely scenario is that this SN was the explosion of a starin a binary system, whose hydrogen envelope has been
removed by binary interactions. For SNe Ib in our sample we found that this scenario may be applicable to SNe
1984L, 2008bo, and 2009jf. It is also interesting to notethat the binary scenario is significantly more prevalentin our SNe Ib samples (3 out of 5 SNe) compared to SNe
Ic (1 out of 6 SNe), but further investigation with more
samples is necessary to confirm this indication firmly.
It is interesting to note that type IIb SNe, whose spectral evolution showed transition from type II to type Ib,
already show evidence that points to a star in a binary
system as the progenitor. Aldering et al. (1994) showedthat the SED of SN 1993J progenitor could not be fit
with a single star SED; further, Maund et al. (2004)
reported the unambiguous detection of the companion
star with post-explosion observation. Indication of binarity was also found in recent IIb events: SN 2008ax(Crockett et al. 2008b) and SN 2011dh (Bersten et al.
2012). Based on the similarities, it is possible that bothtype IIb and Ib SNe have similar binary progenitors.
With the information on SN host cluster age andmetallicity, we derive the maximum mass of the stars
still present in the cluster. As the most massive stars
dies first, any of the remaining stars would not exceed themass of the SN progenitor exploded just recently. The
age of the cluster is equal to the lifetime of the SN progen-12

Kuncarayakti et al.

Figure 13. IFU FoV and extracted cluster spectra for the SN 2009jf site. Figure annotations are the same as in Figure 3.

Table 3Results for SN Ib sites
SN site
1983N
1983N
1984L
1999ec1999ec2008bo2008bo2009jf2009jf2009jf2009jfObject
SC-A*
SC-B
SC*
SC-A*
SC-B
SC-A*
SC-B
SC-A*
SC-B
SC-C
SC-D

Offset/”(pc)a2.6 (57)
3.0 (66)
1.6 (150)
0.8 (90)
3.3 (370)
3.1 (330)
3.5 (380)
0.0 (0)1.4 (230)
1.0 (160)
1.2 (200)(O3N2)
–
–
–
8.49
8.51
–
–
–
8.42
8.39
8.50

(N2)

12+log(O/H)

Z/Z⊙

8.67
8.61
8.31
8.51
8.53
8.74
8.59
8.55
8.48
8.46
8.57

1.02+0.53−0.34
0.89+0.46−0.30
0.45+0.13−0.16
0.71+0.30−0.30
0.74+0.04
−0.02
+0.62
1.20−0.41
0.85+0.44−0.29
0.78+0.39−0.27
0.66+0.08−0.08
0.63+0.09−0.09
0.81+0.12
−0.12

8.67
8.61
8.31
8.53
8.55
8.74
8.59
8.55
8.53
8.52
8.63

HαEW/Å

Age/Myr

M/M⊙

23.32 ± 4.19
1693 ± 728
2.93 ± 0.49
384.50 ± 46.14
424.10 ± 72.09
3.13 ± 0.53
56.37 ± 48.48
1.38 ± 0.12
140.6 ± 23.90
88.71 ± 9.76
80.36 ± 9.64

7.22+0.27−0.42
2.62+0.65−1.26
18.0+2.18−2.21
5.34+0.15−0.35
5.06+0.40
−0.71
+1.03
13.5−0.40
6.37+5.92−0.24
18.2+0.77−0.52
6.02+0.16−0.16
6.36+0.13−0.08
6.25+0.04−0.05

26.4−0.8+1.4–
13.5−0.9+1.1
38.0−1.5+5.0
41.6−4.8+14.2−0.5
14.9+0.4
29.3−13.0+0.9
12.4−0.5+0.3
34.7−0.9+1.2
32.2−1.0+0.6
29.7−0.2+0.1

a Offset between SN and approximate cluster center.
* SN parent cluster.

itor, and since the lifetime of a single star is mainly governed by its initial mass, the lifetime of the SN progenitor could be used to estimate its initial mass. With thismethod we determined the main-sequence mass of the SN
progenitors in our sample by comparing to Padova stellar
evolution models, adopting the metallicity of the parent
cluster. We used the models by Bressan et al. (1993) for
solar metallicity and Fagotto et al. (1994) for 0.4 solar
metallicity. The resulting mass along with metallicity
information for each SN progenitor is plotted on massmetallicity space in Figure 14. Theoretical predictionsof SN progenitors by Georgy et al. (2009) are overlaid tomake the comparison readily available. It is immediately
apparent that the theoretical models and observational
data points do not agree very well – only one occurrenceof observational data falls into the right theoretical prediction for each Ib/c type (SNe 1983N and 1964L). In
spite of this, we argue that the relative comparison of
the mass of progenitor star of different SN types (i.e.
Ib versus Ic) should be robust regardless of the stellar
evolution model used. We also compare our results ofprogenitor mass and local environment age with otherobservational results using different methods, summarized in Table 4. In general our results do not contra-

dict the findings of other studies, except probably for
SN 1984L. This provides a strong confirmation of thevalidity of our method. However, we note that there isalways probability that we are suffering from projection
effects which may cause apparent association between
the SN and an otherwise unrelated stellar population,
resulting in a chance superposition. This issue is further addressed in Paper II, resulting in a 50% chancesuperposition estimate. Nevertheless our method offers
the current best determination of SN progenitor age andmetallicity from the SN local environment. Median distance of objects in this study is ∼15 Mpc (1” corresponds to 70 pc), or redshift 0.0035 (for H0 = 70 km s−1
Mpc−1 ), the smallest compared to other similar studies.
For example the median redshift (distance) of objects inAnderson et al. (2010) is 0.005 (21 Mpc), Modjaz et al.
(2011) 0.017 (72 Mpc), Leloudas et al. (2011) 0.022 (94Mpc), Sanders et al. (2012) 0.036 (154 Mpc) (Table 8 ofSanders et al. 2012).
In this work we suggest that SNe Ic originate from
more massive progenitors than SNe Ib. The progenitor
mass of SN Ic averages 42.9 ± 38.2 M⊙ , while for SN
Ib the average progenitor mass is 21.0 ± 11.0 M⊙ . The
high O3N2 metallicity of SN Ic sites supports this con-

SN site IFU spectroscopy – Ib/c progenitors

13

Figure 14. SN Ib/c progenitors overplotted on mass-metallicity space; Ic progenitors are indicated with purple triangles and Ib progenitors
are indicated with green diamonds. Theoretical predictions of progenitors of each SN type by Georgy et al. (2009) are drawn as colored
regions.

clusion that SN Ic progenitors have mass within the WR
star range. We note that the large deviation in SN Ic
average progenitor mass is caused by the very high determined mass of SN 1964L, ∼ 120 M⊙ . If we omit thisone SN the average progenitor mass for SN Ic is reduced
to 27.5 ± 6.7 M⊙ – still higher than SN Ib progenitor average and consistent with WR star mass. The statisticalsignificance of the Ib and Ic progenitor mass differenceis 1.3σ, and the inclusion of SN 1964L will slightly reduce it into 1.1σ. Our results also show some examples
where the progenitor may have originated from close binary systems, considering the old age of the parent stellar population. This is consistent with the findings of
Leloudas et al. (2011), which suggests that both single
or binary progenitor scenarios are at work for SN Ib/c

production. Recent finding by Sana et al. (2012) showsthat binary interaction may affect 70% or more of themassive star population.
Considering the two channels of high and low massprogenitors possible for SN Ib/c, it is interesting to compare it with the derived initial masses of the compact
remnants in the Galaxy. Magnetars are believed to beformed by rapidly rotating massive stellar cores, and thismechanism would not work if the star enters the redsupergiant phase where magnetic breaking between thestellar core and envelope may spin down the core rotation. Therefore, a very high mass star (& 40 M⊙ ) thatcan lose a significant portion of its hydrogen envelope
prior to SN is required as the progenitor of magnetars.
Several studies have confirmed this by studying the host

14

Kuncarayakti et al.
Table 4Mass and age of SN Ib/c progenitors from this work, compared with other determinations
SN

Mass (this w.)

Age (this w.)

Mass (ref.)Age (ref.)Method (ref.)

Reference

Ic 1964L
Ic 1994I
Ic 2000ew

120 M⊙
17.9 M⊙–
33.9 M⊙–
33.7 M⊙

3.28 Myr–
5.75 Myr–
5.78 Myr–––. 6 Myr–5.75 Myr––SN properties
environment CMD
nondetection
SC color
nondetection

Ic 2007gr
Ic 2009em
Ib 1983N
Ib 1984L

24.4 M⊙
27.7 M⊙
26.4 M⊙
13.5 M⊙

7.84 Myr
6.84 Myr
7.22 Myr
18.0 MyrIb 1999ec
Ib 2008bo
Ib 2009jf

38.0 M⊙
14.9 M⊙–
12.4–34.7 M⊙
12.4–34.7 M⊙
12.4–34.7 M⊙

5.34 Myr
13.5 Myr
6–18 Myr
–
–
–

–
15 M⊙
–
12–40 M⊙–
& 40 M⊙ , or
low-mass binary
28 or 12-9 M⊙
–
–
20 M⊙
& 30 M⊙& 50 M⊙
MV & −8.7––&20–25 M⊙
25–30 M⊙
.8–25 M⊙

7 or 20–30 Myr
–
–
–
–
–
–
–
9.0 Myr–––

SC color––
SN properties
SN properties
SN properties
nondetection–
site HβEW
SN properties
SN properties
SC color–
Nomoto et al. (1994)
Van Dyk et al. (2003)
Maund & Smartt (2005)
Whitmore et al. (2010)
Maund et al. (2005),
Gal-Yam et al. (2005)
Crockett et al. (2008a)––
Schlegel & Kirshner (1989)
Swartz & Wheeler (1991)
Baron et al. (1993)
Van Dyk et al. (2003)–
Sanders et al. (2012)
Sahu et al. (2011)
Valenti et al. (2011)
Valenti et al. (2011)

Ic 2004gt

Note. — CMD: color-magnitude diagram; SC: star cluster

star clusters of the magnetars (e.g. Muno et al. 2006),
but Davies et al. (2009) showed that the magnetar SGR
1900+14 may have had a low mass progenitor of around17 M⊙ . Therefore, the SN that produced those magnetars should also came from both massive and lower-massstars, and the SN needs to be a stripped-envelope event
to be able to produce rapid core rotation that eventually
gave birth to the magnetar. In context with SN Ib/cprogenitor initial mass derived from our study, the two
results are in line. More samples of both Ib/c SN andmagnetar progenitors would be beneficial to establish afirm connection between the two.
We note that this study is based on the assumptionthat the SN progenitor had been a member of the apparent host star cluster present at the explosion site. While
this assumption might not necessarily be true, we argue
that it is more likely that the associated cluster is thereal parent stellar population of the SN progenitor rather
than the diffuse background stellar population. The hostcluster has been revealed to have very young age, thus the
IMF implies higher probability of having high-mass stars
compared to the background stellar population which issignificantly older than the few Myr age of the prominent
cluster. We discuss the probability of contamination byolder, invisible clusters in the field in Paper II, where
the effect is more important for type II SN progenitors,
which are presumably older than SN Ib/c progenitors.
We also present our mass estimate if we only consider
the high-association cases only, i.e. SNe within 150 pc
of the host cluster center. This 150 pc is about the intermediate size between classical and giant HII regions(Crowther 2013), as most of our clusters are apparentlyof around this size. With this limitation, the mean progenitor mass of SNe Ic reduces to 27.5 ± 6.7 M⊙ , and SN
Ib progenitors to 22.6 ± 12.1 M⊙ . This would not change
the aforementioned conclusion.
5. SUMMARY

We present the results of our investigation of nearby
SNe Ib/c explosion sites using integral field spectroscopy(IFS) technique, performed using UH88/SNIFS and
Gemini/GMOS. Taking advantage of IFS, we spatially
identified star clusters at the explosion sites and extracted their respective spectra for the purpose of analysis. From the spectra we derived the metallicities of theclusters in terms of 12+log(O/H) using the strong line
method, and age using comparison of observed Hα emission equivalent width with theoretical SSP models from
Starburst99.
The method employed in this study offers the best
available determination of SN progenitor natal metallicity, probing a very localized region specifically the parent stellar population from which the SN progenitor wasborn. This minimizes the effect of contamination fromother populations and definitely is more reliable compared to metallicity determinations using proxies. As
metallicity is one important parameter in context of SNe
Ib/c progenitor studies, our result provides an important insight in this field. We found indication that themetallicity of SNe Ic explosion sites is on average higher
than SNe Ib sites, by ∼ 0.1 dex. This result is in accordance with Leloudas et al. (2011) and Sanders et al.
(2012) who also found indication that SN Ic explosion
sites are more metal-rich compared to SN Ib sites, although not statistically significant, and Modjaz et al.
(2011) who suggest the same conclusion with results theyclaim to be statistically significant.
The age of the SN progenitor host cluster is considered as the lifetime of the progenitor star. Comparing
with Padova stellar evolution models, we are able to derive initial mass of SNe Ib/c progenitors from the ages of
their parent star cluster. We found that SNe Ic explosion
sites have younger age than SNe Ib, indicating that theyarise from higher mass progenitors than SNe Ib. The
derived progenitor mass from host cluster age is significantly higher for SN Ic, over 42 M⊙ versus 21 M⊙ for SN
Ib progenitors. We note that these derived average progenitor mass were derived from a sample that includes
sub-WR mass progenitors (. 25 M⊙ ) which may be interpreted as binary progenitors. If we consider the sin-

SN site IFU spectroscopy – Ib/c progenitors
gle progenitors only, SN Ic progenitors average 47.9 M⊙
while SN Ib progenitor mass average is 32.2 M⊙ – still
attesting that SN Ic progenitors are the more massive
ones. Further, if only SNe showing high association withthe parent clusters are considered, the average progenitor mass estimates would reduce to 27.5 and 22.6, for
SNe Ic and Ib respectively.
In general, our findings support the current picture of
stripped envelope (Ib/c) SN progenitors: SNe Ic tend tohave more massive progenitors and more metal-rich thanSNe Ib, and for both SN types interacting massive binarystars may comprise a fraction of the progenitors of the
SNe.

15

(United States), the Science and Technology Facilities
Council (United Kingdom), the National ResearchCouncil (Canada), CONICYT (Chile), the Australian
Research Council (Australia), Ministério da Ciência,
Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnologı́a e Innovación Productiva (Argentina).
The authors wish to recognize and acknowledge the verysignificant cultural role and reverence that the summitof Mauna Kea has always had within the indigenous
Hawaiian community. We are most fortunate to have theopportunity to conduct observations from this mountain.
Facilities:(GMOS).

UH88(SNIFS,OPTIC),

Gemini-N

REFERENCES

We acknowledge the anonymous referee for helpfulcomments and suggestions. H.K. acknowledges generous support from the Japanese government MEXT
(Monbukagakusho) scholarship. Useful help from R.
Pain, S. Rodney, and P. Weilbacher on working with
datacubes is appreciated. We thank G. Leloudas for
carefully reading the draft and providing importantcomments. We also thank J. Sollerman and F. Taddia
for helpful comments on the draft of the manuscript. We
acknowledge excellent support from Gemini Observatory
staffs for our observation. This work is based on thedata collected by using the Gemini Telescope, theopportunity for which was made available by making
use of the inter-observatory time-exchange framework
between Gemini and Subaru Observatories. This work
is based on the data by using the University of Hawaii
88-inch Telescope (UH88), for which the telescope time
was afforded by the funding from National Astronomical
Observatory of Japan. This work was supported inpart by a JSPS core-to core program ”International
Research Network for Dark Energy” and by JSPS
research grants. The work of K.M. is supported byWorld Premier International Research Center Initiative(WPI Initiative), MEXT, Japan, and Gant-in-aid for
Scientific Research (23740141). G.A. was supported by
the Director, Office of Science, Office of High Energy
Physics, of the U.S. Department of Energy underContract No. DE-AC02-05CH11231. SNIFS on theUH 2.2-m telescope is part of the Nearby Supernova
Factory II project, a scientific collaboration among theCentre de Recherche Astronomique de Lyon, Institut dePhysique Nucléaire de Lyon, Laboratoire de Physique
Nucléaire et des Hautes Energies, Lawrence Berkeley
National Laboratory, Yale University, University ofBonn, Max Planck Institute for Astrophysics, Tsinghua
Center for Astrophysics, and the Centre de Physiquedes Particules de Marseille. This research has madeuse of the SIMBAD database and ALADIN, operated
at CDS, Strasbourg, France. This research has madeuse of the NASA/IPAC Extragalactic Database (NED)
which is operated by the Jet Propulsion Laboratory,
California Institute of Technology, under contract with
the National Aeronautics and Space Administration.
Based on observations obtained at the Gemini Observatory, which is operated by the Association of
Universities for Research in Astronomy, Inc., under acooperative agreement with the NSF on behalf of theGemini partnership: the National Science Foundation

Adamo, A., Smith, L. J., Gallagher, J. S., et al. 2012, MNRAS,
426, 1185
Aldering, G., Humphreys, R. M., & Richmond, M. 1994, AJ, 107,
662
Aldering, G., Adam, G., Antilogus, P., et al. 2002, Proc. SPIE,
4836, 61
Aldering, G., Antilogus, P., Bailey, S., et al. 2006, ApJ, 650, 510
Allington-Smith, J., Murray, G., Content, R., et al. 2002, PASP,
114, 892
Anders, P., & Fritze-v. Alvensleben, U. 2003, A&A, 401, 1063
Anderson, J. P., & James, P. A. 2008, MNRAS, 390, 1527
Anderson, J. P., Covarrubias, R. A., James, P. A., Hamuy, M., &Habergham, S. M. 2010, MNRAS, 407, 2660
Anderson, J. P., Habergham, S. M., James, P. A., & Hamuy, M.
2012, MNRAS, 424, 1372
Arribas, S., Mediavilla, E., Garcı́a-Lorenzo, B., del Burgo, C., &Fuensalida, J. J. 1999, A&AS, 136, 189
Asplund, M., Grevesse, N., Sauval, A. J., Allende Prieto, C., &Kiselman, D. 2004, A&A, 417, 751
Bacon, R., Copin, Y., Monnet, G., et al. 2001, MNRAS, 326, 23
Barbon, R., Buondı́, V., Cappellaro, E., & Turatto, M. 1999,
A&AS, 139, 531
Baron, E., Young, T. R., & Branch, D. 1993, ApJ, 409, 417
Bastian, N., & Goodwin, S. P. 2006, MNRAS, 369, L9Berg, D. A., Skillman, E. D., & Marble, A. R. 2011, ApJ, 738, 2
Bersten, M. C., Benvenuto, O. G., Nomoto, K., et al. 2012, ApJ,
757, 31Blaylock, M., Branch, D., Casebeer, D., Millard, J., Baron, E.,
Richardson, D., & Ancheta, C. 2000, PASP, 112, 1439
Boffi, F. R., Sparks, W. B., & Macchetto, F. D. 1999, A&AS, 138,
253
Boissier, S., & Prantzos, N. 2009, A&A, 503, 137
Bressan, A., Fagotto, F., Bertelli, G., & Chiosi, C. 1993, A&AS,
100, 647
Bressert, E., Bastian, N., Gutermuth, R., et al. 2010, MNRAS,
409, L54
Clocchiatti, A., Wheeler, J. C., Benetti, S., & Frueh, M. 1996,
ApJ, 459, 547
Clocchiatti, A., Wheeler, J. C., Kirshner, R. P., et al. 2008,
PASP, 120, 290
Crockett, R. M., Smartt, S. J., Eldridge, J. J., et al. 2007,
MNRAS, 381, 835
Crockett, R. M., Maund, J. R., Smartt, S. J., et al. 2008a, ApJ,
672, L99
Crockett, R. M., Eldridge, J. J., Smartt, S. J., et al. 2008b,
MNRAS, 391, L5
Crowther, P. A. 2007, ARA&A, 45, 177
Crowther, P. A. 2013, MNRAS, 428, 1927
Davies, B., Figer, D. F., Kudritzki, R.-P., et al. 2009, ApJ, 707,
844
Elias-Rosa, N., Van Dyk, S. D., Li, W., et al. 2011, ApJ, 742, 6
Eldridge, J. J., & Tout, C. A. 2004, MNRAS, 353, 87
Eldridge, J. J., Izzard, R. G., & Tout, C. A. 2008, MNRAS, 384,
1109
Eldridge, J. J., Fraser, M., Smartt, S. J., Maund, J. R., &Crockett, R. M. 2013, arXiv:1301.1975

16

Kuncarayakti et al.

Fagotto, F., Bressan, A., Bertelli, G., & Chiosi, C. 1994, A&AS,
105, 29
Filippenko, A. V. 1982, PASP, 94, 715
Folatelli, G., & Morrell, N. 2009, Central Bureau Electronic
Telegrams, 1807, 1
Fraser, M., Ergon, M., Eldridge, J. J., et al. 2011, MNRAS, 417,
1417
Gal-Yam, A., Fox, D. B., Kulkarni, S. R., et al. 2005, ApJ, 630,
L29
Gaskell, C. M., Cappellaro, E., Dinerstein, H. L., et al. 1986,
ApJ, 306, L77
Georgy, C., Meynet, G., Walder, R., Folini, D., & Maeder, A.
2009, A&A, 502, 611
Gerardy, C. L., Fesen, R. A., Nomoto, K., et al. 2002, PASJ, 54,
905
Gogarten, S. M., Dalcanton, J. J., Murphy, J. W., et al. 2009,
ApJ, 703, 300
Heger, A., Fryer, C. L., Woosley, S. E., Langer, N., & Hartmann,
D. H. 2003, ApJ, 591, 288
Hook, I. M., Jørgensen, I., Allington-Smith, J. R., et al. 2004,
PASP, 116, 425
Howell, S. B., & Tonry, J. L. 2003, BAAS, 35, 1235
Hunter, D. J., Valenti, S., Kotak, R., et al. 2009, A&A, 508, 371
Immler, S., Brown, P. J., & Milne, P. 2008, The Astronomer’s
Telegram, 1463, 1
Immler, S., & Brown, P. J. 2008, The Astronomer’s Telegram,
1481, 1
Kuncarayakti, H., Doi, M., Aldering, G., et al. 2013, submitted(Paper II)
Kotulla, R., Fritze, U., Weilbacher, P., & Anders, P. 2009,
MNRAS, 396, 462
Lada, C. J., & Lada, E. A. 2003, ARA&A, 41, 57
Lantz, B., Aldering, G., Antilogus, P., et al. 2004, Proc. SPIE,
5249, 146
Leitherer, C., Schaerer, D., Goldader, J. D., et al. 1999, ApJS,
123, 3
Leloudas, G., Gallazzi, A., Sollerman, J., et al. 2011, A&A, 530,
A95
Maund, J. R., Smartt, S. J., Kudritzki, R. P., Podsiadlowski, P.,& Gilmore, G. F. 2004, Nature, 427, 129
Maund, J. R., & Smartt, S. J. 2005, MNRAS, 360, 288
Maund, J. R., Smartt, S. J., & Schweizer, F. 2005, ApJ, 630, L33
Modjaz, M., Kewley, L., Bloom, J. S., et al. 2011, ApJ, 731, L4
Monard, L. A. G. 2009, Central Bureau Electronic Telegrams,
1798, 1

Muno, M. P., Clark, J. S., Crowther, P. A., et al. 2006, ApJ, 636,
L41
Navasardyan, H., Benetti, S., Harutyunyan, A., et al. 2008,
Central Bureau Electronic Telegrams, 1325, 1
Navasardyan, H., & Benetti, S. 2009, Central Bureau Electronic
Telegrams, 1806, 1
Nomoto, K., Yamaoka, H., Pols, O. R., et al. 1994, Nature, 371,
227
Pastorello, A., Zampieri, L., Turatto, M., et al. 2004, MNRAS,
347, 74Pérez-Montero, E., & Contini, T. 2009, MNRAS, 398, 949
Pettini, M., & Pagel, B. E. J. 2004, MNRAS, 348, L59
Podsiadlowski, P., Joss, P. C., & Hsu, J. J. L. 1992, ApJ, 391, 246
Portegies Zwart, S. F., McMillan, S. L. W., & Gieles, M. 2010,
ARA&A, 48, 431
Porter, A. C., & Filippenko, A. V. 1987, AJ, 93, 1372
Porter, A. C. 1993, PASP, 105, 1250
Prantzos, N., & Boissier, S. 2003, A&A, 406, 259
Sahu, D. K., Gurugubelli, U. K., Anupama, G. C., & Nomoto, K.
2011, MNRAS, 413, 2583
Sana, H., de Mink, S. E., de Koter, A., et al. 2012, Science, 337,
444
Sanders, N. E., Soderberg, A. M., Levesque, E. M., et al. 2012,
ApJ, 758, 132
Sramek, R. A., Panagia, N., & Weiler, K. W. 1984, ApJ, 285, L59
Sauer, D. N., Mazzali, P. A., Deng, J., et al. 2006, MNRAS, 369,
1939
Schlegel, E. M., & Kirshner, R. P. 1989, AJ, 98, 577
Smartt, S. J., Eldridge, J. J., Crockett, R. M., & Maund, J. R.
2009, MNRAS, 395, 1409
Smartt, S. J. 2009, ARA&A, 47, 63
Stockdale, C. J., Weiler, K. W., Immler, S., et al. 2008, The
Astronomer’s Telegram, 1477, 1
Swartz, D. A., & Wheeler, J. C. 1991, ApJ, 379, L13
Tanaka, M., Kawabata, K. S., Maeda, K., Hattori, T., & Nomoto,K. 2008, ApJ, 689, 1191
Valenti, S., Fraser, M., Benetti, S., et al. 2011, MNRAS, 416, 3138
van Dyk, S. D. 1992, AJ, 103, 1788
Van Dyk, S. D., Li, W., & Filippenko, A. V. 2003, PASP, 115, 1
Van Dyk, S. D., Davidge, T. J., Elias-Rosa, N., et al. 2012, AJ,
143, 19
Vink, J. S., de Koter, A., & Lamers, H. J. G. L. M. 2001, A&A,
369, 574
Weiler, K. W., Sramek, R. A., Panagia, N., van der Hulst, J. M.,& Salvati, M. 1986, ApJ, 301, 790
Whitmore, B. C., Chandar, R., Schweizer, F., et al. 2010, AJ,
140, 75