Serb. Astron. J. } 189 (2014), 41 - 51

UDC 524.354–77
Original scientific paper

DOI: 10.2298/SAJ140605001H

RADIO-CONTINUUM EMISSION FROM THE YOUNGGALACTIC SUPERNOVA REMNANT G1.9+0.3
A. Y. De Horta1 , M. D. Filipović1 , E. J. Crawford1 , F. H. Stootman1 , T. G. Pannuti2 ,L. M. Bozzetto1 , J. D. Collier1 , E. R. Sommer1 and A. R. Kosakowski2
1

University of Western Sydney, Locked Bag 1797, Penrith South, DC, NSW 1797, Australia
E–mail: a.dehorta@uws.edu.au, m.filipovic@uws.edu.au, e.crawford@uws.edu.au2Space Science Center, Department of Earth and Space Sciences, Morehead State University,
235 Martindale Drive, Morehead, KY 40351 USA
E–mail: t.pannuti@moreheadstate.edu(Received: June 5, 2014; Accepted: June 18, 2014)

SUMMARY: We present an analysis of a new Australia Telescope Compact Array (ATCA) radio-continuum observation of supernova remnant (SNR) G1.9+0.3,
which at an age of ∼181±25 years is the youngest known in the Galaxy. We
analysed all available radio-continuum observations at 6-cm from the ATCA andVery Large Array. Using this data we estimate an expansion rate for G1.9+0.3
of 0.563%±0.078% per year between 1984 and 2009. We note that in the 1980’s
G1.9+0.3 expanded somewhat slower (0.484% per year) than more recently (0.641%
per year). We estimate that the average spectral index between 20-cm and 6-cm,
across the entire SNR is α=–0.72±0.26 which is typical for younger SNRs. At 6cm, we detect an average of 6% fractionally polarised radio emission with a peakof 17%±3%. The polarised emission follows the contours of the strongest of X-ray
emission. Using the new equipartition formula we estimate a magnetic field strengthof B≈273 µG, which to date, is one of the highest magnetic field strength found for
any SNR and consistent with G1.9+0.3 being a very young remnant.
Key words. ISM: individual objects: G1.9+0.3 – ISM: supernova remnants – radio
continuum: ISM – supernovae: general

1. INTRODUCTION
It is widely accepted that current catalogues
have a distinct deficit of young Galactic supernova
remnants (SNRs), that is, SNRs <2000 years old,with only ∼10 confirmed out of a predicted ∼50 (vanden Bergh and Tammann 1991, Cappellaro 2003).
Of these confirmed SNRs, G1.9+0.3 is of particularinterest as it is believed to be the youngest in the
Milky Way (MW), i.e. ∼ 150 years old (Reynolds etal. 2008, Green et al. 2008, Reynolds et al. 2009,
Carlton et al. 2011a,b).
Originally identified as a probable SNR by
Green and Gull (1984) at 4.9 GHz using the Karl G.
Jansky Very Large Array (VLA), G1.9+0.3 was described as a shell source with an approximate brightness slightly less than that of the Tycho and Kepler
41

A. Y. DE HORTA et al.

SNRs with a spectral index of α ∼ −0.71 . Using the
Molonglo Observatory Synthesis Telescope (MOST)
Galactic Survey data, Gray (1994) confirmed theclassification of G1.9+0.3 as an SNR: the source wasdescribed as featuring a shell-like morphology in theradio with an estimated diameter of 1.0 2. Later,
LaRosa et al. (2000) produced a 90-cm image of
G1.9+0.3 using observations from the VLA. They estimated the 20/90-cm spectral index of the SNR to
be α = −0.93 ± 0.25 and the angular diameter to be
1.0 1. Nord et al. (2004) revisited the data collectedby LaRosa et al. (2000) and – through the application of superior data reduction techniques – measured the diameter of G1.9+0.3 to be <10 and placed
it at a distance of <7.8 kpc. Green (2004) estimates
the diameter of G1.9+0.3 based on 1.49 GHz VLA
observations made in 1985 to be 1.0 2. Most recently,
Roy and Pal (2014) measured the H i absorption distance using known anomalous velocity features near
the Galactic Centre (GC) and found a lower limit on
G1.9+0.3 distance from Sun as 10 kpc, some 2 kpc
further away from the GC. Therefore, multiple radio observations have confirmed that G1.9+0.3 has
the smallest angular diameter for a known Galactic
SNR, indicative of its young age.
Green et al. (2008) re-observed G1.9+0.3 at
4.86 GHz using the VLA after Reynolds et al. (2008)
used 2007 Chandra images to show G1.9+0.3 had expanded significantly since 1985 and its X-ray emission appeared to be predominantly synchrotron innature. By comparing these new VLA observations
with the 1985 VLA observations made at 1.49 GHz,
Green et al. (2008) determined that G1.9+0.3 had
expanded by 15% ± 2% over 23 years (∼0.65% peryear). Using the same VLA observations from 1985
and 1989, Gómez and Rodrı́guez (2009) derived an
expansion rate of 0.46%±0.11% and an age of 220±70
45
years. By comparing 2007 and 2009 Chandra Xray images and utilising a simple uniform-expansion
model, Carlton et al. (2011a,b) find an expansion
rate of 0.642% ± 0.049% yr−1 and a flux increaseof 1.7% ± 1.0% yr−1 , ageing the remnant at 156 ±11 yr assuming no deceleration. Murphy, Gaensler
and Chatterjee (2008) found that G1.9+0.3’s flux
density at 843 MHz increased by 1.22±0.24
0.16 % peryear over the last two decades.

Borkowski et al. (2013) suggest that G1.9+0.3
was likely a Type Ia SNe with the shell of its remnant
in free expansion with a velocity ∼18 000 km s−1 .
The ejecta shows spatial asymmetry with prominent
Fe-group elements in the northern rim. Also, we
point out that Abramowski et al. (2014) reportno γ-ray signal from G1.9+0.3 using observations
from the H.E.S.S. (High Energy Stereoscopic System) Cherenkov telescope array.
The presence of polarised emission and spatial
spectral variations are identified by Farnes (2012),
with flatter spectra identified in the NW and SE of
the remnant.
In this paper, we present the results of ourAustralia Telescope Compact Array (ATCA) radiocontinuum observations of G1.9+0.3 made at 20,
13 and 6 cm in 2009. A comprehensive expansion study is conducted by comparing the new 6cm observations with a previously unpublished 6-cm
ATCA radio-continuum observation, made in 1993,
and three 6-cm VLA observations made in 2008, 1989
and 1984 respectively. We also report on the radiocontinuum spectral energy distribution and polarisation properties of this young SNR.

2. OBSERVATIONAL DATA
G1.9+0.3 was observed at 20, 13 and 6 cm
wavelengths on four days in 2009 (Project C1952).
Two of those days being in January 2009 with theremainder in February 2009. The 20-cm and 13-cm
observations, taken on the 2nd and 3rd day, werecarried out simultaneously as they make use of acommon feed-horn. The 6-cm observations taken on
the 1st and 4th day, used four different frequencies(two per day) to improve multi-frequency synthesis (MFS). For this purpose, the miriad (Sault andKilleen 2008) task mfplan was used to select themost appropriate frequencies. Over the four days
G1.9+0.3 was observed with two separate antennaconfigurations for a total of 29 independent baselines
covering a range of spacings from 31 to 6 000 m. See
Table 1 for complete observational details.

Table 1. 2009 ATCA observations of G1.9+0.3.
Date
ATCA Array
Frequency 1
Frequency 2
Bandwidth
Time on source
Primary Calibrator
Secondary Calibrator
1 Spectral index defined as S ∝ ν α

42

Day 1
03 Jan6C
4.672 GHz
5.440 GHz
128 MHz332 min
J1934-638
J1741-312

Day 2
04 Jan6C
1.384 GHz2.368 GHz
128 MHz458 min
J1934-638
J1751-253

Day 3
06 Feb
EW352
1.384 GHz2.368 GHz
128 MHz509 min
J1934-638
J1751-253

Day 4
07 Feb
EW352
4.544 GHz
5.184 GHz
128 MHz1033 minJ1934-638
J1741-312

RADIO-CONTINUUM EMISSION FROM THE YOUNG GALACTIC SNR G1.9+0.3

ing MFS with uniform weighting and were deconvolved using the miriad (Sault and Killeen 2008)
clean and restor tasks, with self calibration being applied to the 6-cm image only. We note that
our corresponding ATCA flux density measurements
are significantly smaller (∼50%) than the VLA estimates of Green et al. (2008). We can attribute thislarge difference to missing short spacings and poorer
uv coverage of the ATCA images.

Fig. 1.
ATCA 20-cm image of Galactic SNR
G1.9+0.3. The blue ellipse in the lower left corner represents the synthesised beam of 10.00 9 × 5.00 4
at PA=–0.◦ 5. Contours are drawn at 3σ, 5σ, 8σ,
12σ, 17σ, 23σ, 30σ, 38σ 47σ and 57σ (σ =0.22 mJy/beam).

Fig. 3.
ATCA 6-cm image of Galactic SNR
G1.9+0.3. The blue ellipse in the lower left corner represents the synthesised beam of 2.00 8 × 1.00 2
at PA=–0.◦ 5. Contours are drawn at 3σ, 5σ, 8σ,
12σ, 17σ, 23σ, 30σ, 38σ 47σ and 57σ (σ = 0.07
mJy/beam).
3. RESULTS
3.1. G1.9+0.3 Expansion and Age

Fig. 2.
ATCA 13-cm image of Galactic SNR
G1.9+0.3. The blue ellipse in the lower left corner represents the synthesised beam of 6.00 1 × 2.00 9
at PA=–0.◦ 5. Contours are drawn at 3σ, 5σ, 8σ,
12σ, 17σ, 23σ, 30σ, 38σ 47σ and 57σ (σ =0.32 mJy/beam).
In Figs. 1 through 3 we show our new ATCA
2009 images of G1.9+0.3 at 20-cm, 13-cm and 6cm respectively. All these images were formed us-

A simple way to determine the age (in years)of a young SNR is to compare two images of the
SNR taken at different epochs and to measure thepercentage expansion the SNR has undergone over
the time between the observations. Since we knowthat the SNR will have expanded by 100% in the intervening period between the SN explosion and thelater observation, we can apply the simple formula,
Age = 100%/ER, where ER is the percentage expansion the SNR has undergone over the time between
the observations (in years).
Ideally, to most accurately determine the expansion rate of an SNR, one should compare images
from similar observations i.e, at the same wavelengthand having similar, if not identical, uv -coverage, resolution and rms noise.
In the case of G1.9+0.3 the first observations
were made in 1984 using the VLA, with the best image produced from the 6 cm data (Fig. 4, bottom
left). With this in mind, ATCA and VLA archives
43

A. Y. DE HORTA et al.

Table 2. VLA observations of G1.9+0.3.
Date
VLA Array
Frequency
Bandwidth
Time on source
Primary Calibrator
Secondary Calibrator

1984 obs.
26 May 1984
C
4.89 GHz
50 MHz∼10 min
3C286
J1832-105

were searched for all available radio-continuum dataof G1.9+0.3 made at this same wavelength of 6 cm.
For the expansion study carried out in this paper, one ATCA and three VLA observations made at
6-cm were found at different epochs from the original
1984 to 2008.
The archival ATCA observation was taken on
the 10th June 1993 (Project C034; P.I.: A. Gray).
This observation was made in the 6-cm band centred at 4672 and 5440 MHz with a bandwidth (BW)of 128 MHz and the telescope in 6A configuration2 .
Source 1934-638 was used for primary calibrationand source 1748-253 was used for secondary calibration. The observations were done in the so-called”snap-shot” mode, totalling ∼1 hour of integration
spread equally over a 12 hour period. With very few
short baselines and poor uv -coverage, resulting rms
of 0.2 mJy beam−1 is the highest amongst all theanalysed observations. Consequently, the data forthis observation are of very poor quality and, while
the results are still presented here, we exclude measurements from this image in our determination of
expansion rates and age. The archival VLA observations were from the 1984 (Project AG0146), 1989
(Project AB0544) and 2008 (project AG0793), see
Table 2 for details.
All these observations of G1.9+0.3 were reduced and analysed with the miriad (Sault, Teuben
and Wright 1995) and karma (Gooch 1995) software
packages.
As the resolutions of the produced images
varied (due to the various array configuration,observational periods and therefore resultant uv coverage), the resolutions of all the images weresmoothed/convolved to match the image with thelowest resolution (900 × 400 at a PA of 0◦ ), see Fig. 4.
Since the rms noise of the resultant images
also varied (see Table 3), it was decided not to try to
determine the expansion by looking at how the shock
front moved between epochs, but by looking at how
the radially averaged shell profile peak moved from
epoch to epoch.
Using RA=17h 48m 45 .s 4, Dec=−27◦ 100 0600 as
the centre of G1.9+0.3 we produced normalised shell
profiles (Fig. 5), averaged over all angles, for each of
the images shown in Fig. 4.

1989 obs.
23 June 1989
BC
4.89 GHz
50 MHz∼10 min
3C286
J1751-253

2008 obs.
12 March 2008
C
4.89 GHz
50 MHz∼30 min
3C286
J1751-253

Table 3. G1.9+0.3 rms noise (1σ) of 6 cm images
shown in Fig. 4. All five images shown in Fig. 4
have matched resolution of 900 ×400 at a PA of 0◦ .
Telescope

Date

VLA
VLA
ATCA
VLA
ATCA

1984
1989
1993
2008
2009

Image rms
(mJy/beam)
0.09
0.09
0.20
0.06
0.06

From the shell profiles in Fig. 5 we have determined the expansion rate in arc-seconds per year,
percentage expansion per year, the averaged expansion velocity in km s−1 (assuming a distance of
8.5 kpc3 ), and age in years. These results are summarised in Tables 4 though 7, respectively.
Table 4. Expansion rate of G1.9+0.3 in arc-seconds
per year of radially averaged radio-continuum emission peak.

1984
1989
2008
2009

1984
0
0.148
0.189
0.182

1989

2008

2009

0
0.200
0.191

0
0

0

Table 5. % Expansion of G1.9+0.3 per year ofradially averaged radio-continuum emission peak.

1984
1989
2008
2009

1984
0
0.484
0.620
0.598

1989

2008

2009

0
0.641
0.612

0
0

0

2 We combined these two frequencies into a single 1 GHz band, see the image shown in Fig. 4 (middle left).
3 Distance estimates to G1.9+0.3 vary between ∼7.8 kpc (Nord et al.

as the most likely distance – suggested by Reynolds et al. (2008).

442004) and 10 kpc (Roy and Pal 2014). We use 8.5 kpc

RADIO-CONTINUUM EMISSION FROM THE YOUNG GALACTIC SNR G1.9+0.3

Fig. 4. Matched resolution (900 × 400 at a PA of 0◦ ) 6-cm images of Galactic SNR G1.9+0.3 (centred at
RA(J2000)=17h 48m 45 .s 4, Dec(J2000)=−27◦ 100 0600 ) at multiple epochs. Left to right, top to bottom, 2009
ATCA, 2008 VLA, 1993 ATCA, 1989 VLA and 1984 VLA.
45

A. Y. DE HORTA et al.

1984 - 30.50
1989 - 31.25
1993 - 33.00
2008 - 35.00
2009 - 35.00

1

Normalised Flux Density

0.8

0.6

0.4

0.2

0
10

0

20

30

40

50

60

Radius (arcsec)

Fig. 5. Normalised shell profiles averaged over all angles for each image of G1.9+0.3 in Fig. 4.
Table 6. Estimated age of G1.9+0.3 in years.
1984
1989
2008
2009

1984
0
206
161
167

1989

2008

2009

0
156
163

0
0

0

Table 7.
Speed of radially averaged radiocontinuum emission peak in km s−1 of G1.9+0.3.
1984
1989
2008
2009

1984
0
5 950
7 620
7 350

1989

2008

2009

0
8 070
7 710

0
0

0

In Tables 4 and 5 we show the expansion of
G1.9+0.3 over the period between 1984 and 2009.
The mid range expansion over this period (excluding the 1993 observations) is 0.563%±0.078% yr−1
or 0.174±0.026 arcsec yr−1 . However, we notethat between 1984 and 1989, G1.9+0.3 expanded ata somewhat slower rate (0.484% yr−1 ) which was
also estimated by Gómez and Rodrı́guez (2009) at
0.46% ± 0.11% based on 20-cm VLA data from thesame period. Since 1989, G1.9+0.3 appears to expand at a faster rate of up to 0.641% per year which46

is in excellent agreement with the X-ray estimatesof Carlton et al. (2011a,b) of 0.642%±0.049% andGreen et al. (2008) using VLA observations. Thismay be an indication that perhaps the shock has”broken through” to a region of lower density andthus accelerated. The mid range expansion rate derived here, yields an upper age limit of 181±25 years(Table 6) assuming a constant expansion rate since
the SN event. This dates the SN event back to theyear 1828 (±25).
Similarly, the speed at which the radiallyaveraged radio-continuum emission peak is moving(assuming a distance to G1.9+0.3 of 8.5 kpc) issomewhat slower in the 1980’s (∼6 000 km sec−1 )than later, when it speeds up to ∼8 000 km sec−1(Table 7). The speed of radially averaged radiocontinuum emission peak should not be confusedwith the expansion velocity of the SNR shock front,
which has been estimated at ∼18 000 km sec−1 by
Borkowski et al. (2013).
As our determination of the radially averaged
radio-continuum emission peak speed is dependent
on the distance to the SNR we estimate that at thelower end (between 1984 and 1989) the speed varies
between 5 500 km sec−1 (at a distance of 7.8 kpc)
and 7 000 km sec−1 (at a distance of 10 kpc). Morerecently (between 1989 and 2009), the speed varies
between 7 400 km sec−1 (at a distance of 7.8 kpc)
and 9 500 km sec−1 (at a distance of 10 kpc).

RADIO-CONTINUUM EMISSION FROM THE YOUNG GALACTIC SNR G1.9+0.3

Fig. 6. The Spectral Index map of G1.9+0.3 overlaid with 20-cm contours (top left; contours are: 3, 5,
8, 12, 12, 17, 23, 30, 38, 47, 57 × 7.5 × 10−4 Jy/beam), 13-cm contours (top right; contours are: 3, 5, 8,
12, 17, 23, 30, 38, 47, 57 × 6.0 × 10−4 Jy/beam), 6-cm contours (bottom left; contours are: 3, 5, 8, 12, 17,
23, 30 × 5.0 × 10−4 Jy/beam) and 2007 Chandra X-ray contours (bottom right; contours are: 33.57, 67.14,
100.7, 134.3, 167.9, 201.4, 235, 268.6 cts/s).
3.2. G1.9+0.3 Spectral Energy Distribution
By matching the resolutions of our 2009
ATCA images at 6-cm and 13-cm to that of the
20-cm image (10.00 9 × 5.00 4 at PA=–0.◦ 5), a three point
spectral index map was created, allowing for the examination of the spatial spectral variations in theremnant (see Fig. 6). In this map, the colour of eachpixel represents the spectral index α across the threeobservational frequencies.
From this map we can see that the radiocontinuum spectral energy distribution across the
NW and SE regions is flatter (α ∼ −0.5) which isalso following the contours of the strongest of Xray emission (so called ”X-ray ears” of G1.9+0.3; see
Fig. 6 – bottom right). This SED flattening in the
NW and SE is also confirmed by Farnes (2012) in
his VLA observations. The steeper (α ∼ −1) radio spectra is dominant in the Northern region of

G1.9+0.3 corresponding to where the radio emission is the strongest and therefore indicating thesynchrotron radio-continuum emission. We also notethat a somewhat steeper spectral index (α < −1.0) is
dominating the inside part of the SNR, while flatter
spectra is at the edges.
We estimate that the average spectral index
across the entire SNR is α = −0.72 ± 0.26 which isflatter than LaRosa et al. (2000) (α = −0.93 ± 0.25),
however, their estimates are based on 20/90 cm flux
density measurements. This may indicate that thesynchrotron emission may be even more dominant
at higher wavelengths (92 cm). Using Green et al.
(2008) flux density estimates at 20 and 6 cm fromtheir 2008 VLA observations, we estimate the spectral index α = −0.62 ± 0.08 which is in good agreement with our ATCA estimates from approximately
one year later. This steeper spectral index is expected for younger SNRs (Bell et al. 2011), and further confirms its young age.
47

A. Y. DE HORTA et al.

3.3. Polarisation of G1.9+0.3
Since the ATCA observations recorded Stokes
parameters Q, U and V , in addition to total intensity I, we were able to determine the polarisation of
G1.9+0.3. In our 6-cm image (Fig. 7) we show theregions of polarised emission for G1.9+0.3. The electric field vectors follow the shell of the SNR aroundmost of the circumference of the SNR, particularly
along its eastern side.
The maximum fractional polarisation is estimated to be P = 17 ± 3% with a mean of 6%. No
reliable polarisation was detected at 20 or 13 cm.
This might indicate a significant depolarisation in
the remnant, however the polarimetric response of
the ATCA is known to be poor at 13-cm.

ever, it can be seen that this pattern is not strictly
followed around the entire remnant. Given the location of G1.9+0.3, towards the Galactic centre, thisis most likely due to Faraday depolarisation.
Farnes (2012) also detected the presence of polarised emission. Our ATCA polarimetric results alsosuggest that the above observed variation is mostconsistent with an ambient B field perpendicular to
the axis of bilateral symmetry indicated by Farnes(2012). Moreover, Farnes (2012) argues that the increased ordering of the B field in the NW as thestrong Faraday depolarisation must also be present.
Farnes (2012) also argues that an intrinsically radially-oriented field could be provided by asystematic gradient in Rotation Measure (RM) of
140 rad m−2 from N to S and can also explain the
depolarisation that we observe in our ATCA images.
3.4. Magnetic Field of G1.9+0.3

Fig. 7. 6-cm ATCA observations of G1.9+0.3.
The blue ellipse in the lower-left corner represents
the synthesised beam width of 10.00 940 × 5.00 384 at
PA=–0.◦ 5. The length of the vectors represents thefractional polarised intensity at each pixel position,and their orientations indicate the mean PA of theelectric field (averaged over the observing bandwidth,
not corrected for any Faraday rotation). The blueline below the beam ellipse represents the length ofa polarisation vector of 100%. The maximum fractional polarisation is 17% ± 3% with a mean of 6%.
Contours at 2.2, 2.8, 4.4, 6.6, 9.4, 13, 17, 21, 26
and 32 mJy beam−1 ).
Typically, young type Ia SNRs exhibit a radially oriented magnetic field (tangentially oriented
electric field), which is to be expected from RayleighTaylor instabilities in a decelerating remnant (Gull
1975, Chevalier 1976). This is consistent with similarly young Galactic SNRs, as well as in the LMC(e.g. Table 3 in Bozzetto et al. (2014)). As we haveplotted electric field vectors, we would expect them
to be tangential to the circumference of the remnant.
We can see in Fig. 7, the orientation of the electricfield vectors roughly follow this arrangement, how4 http://poincare.matf.bg.ac.rs/∼arbo/eqp/

48

We used the new equipartition formulae derived by Arbutina et al. (2012, 2013) based on
the diffusive shock acceleration (DSA) theory of
Bell (1978) to estimate a magnetic field strength.
These formulae are particularly relevant to magnetic field estimation in SNRs, and yield magnetic
field strengths between those given by the classicalequipartition (Pacholczyk 1970) and revised equipartition (Beck and Krause, 2005) methods. We estimate the magnetic field strength of G1.9+0.3 to be
B ≈ 273 µG and the minimum total energy of thesynchrotron radiation to be Emin ≈ 1.8 × 1048 ergs
(see Arbutina et al. 2012, 2013); and corresponding online calculator4 ). For this estimate, we useda spectral index value of α = −0.72, integrated flux
density S1.425 =0.935 Jy at ν=1.425 GHz (Green etal. 2008), distance D=8.5 kpc, SNR radius of r=4600
and filling factor of 0.33. However, if we additionally assume a shock velocity of 18 000 km s−1(as suggested by Borkowski et al. (2013)) thanthe magnetic field strength of G1.9+0.3 becomessomewhat lower (B ≈ 180 µG) and the minimum total energy of the synchrotron radiation isEmin ≈ 7.6 × 1047 ergs. These estimates are very
similar to Arbutina et al. (2012) estimates ofB ≈ 228 µG and Emin ≈ 9.3 × 1047 ergs.
A large magnetic field strength such as this(273 µG) is expected for a young SNR (Bell 2004).
Indeed, this makes G1.9+0.3 a remnant with one of
the highest estimated magnetic field strengths known
to date. For example, other young Galactic SNRs
(Beck and Krause 2005, Arbutinal et al. 2012 (seetheir Table 1)), such as Cas A (B≈ 1250 µG), Kepler (B≈ 414 µG), G349.7+0.2 (B≈ 523 µG) andTycho (B≈ 285 µG), are known remnants with thestrongest magnetic fields. Also, in a Large Magellanic Cloud (LMC) SNR, J0509-6731 (also remnant
from a Type Ia SN explosion) at about 400 yrs age
has magnetic field strength of 168 µG (Bozzetto et al.

RADIO-CONTINUUM EMISSION FROM THE YOUNG GALACTIC SNR G1.9+0.3

2014), while the magnetic field of LMC SNR J0519–
6902 is 171 µG (Bozzetto et al. 2012). The Small
Magellanic Cloud SNR HFPK 443 (Crawford et al.
2014, in press) has a field strength of 90 µG withnumerous other older remnants falling below thesevalues. It is most likely that G1.9+0.3 is going
through an evolutionary stage where the magnetic
field has been amplified (added to simple compression by the shocks), which may explain such a highmagnetic field value (Telezhinsky et al. 2012). The
amplification of magnetic field is a process driven
by very fast shocks of young SNRs. Because of thestrong amplification of magnetic field, a spectral index of α = −0.72, and the location in the surface
brightness-diameter diagram, this SNR is of younger
age, in free expansion stage, and expanding in a low
density environment.
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4. CONCLUSIONS
Here, we have presented new 6-cm, 13-cm
and 20-cm ATCA observations of Galactic SNR
G1.9+0.3 made in 2009. Using the new 6-cm data
and archival 6-cm data we observe that there are indications that the expansion of G1.9+0.3 accelerated
after 1989. Our results are in a broad agreement withthe estimates of expansion made by Reynolds et al.
(2008), Green et al. (2008), Gómez and Rodrı́guez(2009) and Carlton et al. (2011a,b). We find that at∼ 181 yrs, G1.9+0.3 is indeed very young and most
likely the youngest SNR in the Milky Way. This
very young age is also reinforced by the magnetic
field arrangement and strength we estimate.
We make the following findings:- Expansion rate of 0.484% per year between
1984 and 1989;- Expansion rate of 0.641% per year between
1989 and 2009;- Expansion rate of 0.563%±0.078% per year
between 1984 and 2009;- Age of 181 yrs±25 yrs;
- Average spectral index between 20-cm and 6cm, across the entire SNR is α=–0.72±0.26;- 6% fractionally polarised radio emission witha peak of 17%±3%;- Magnetic field strength B≈273 µG;
Acknowledgements – We used the karma andmiriad software package developed by the ATNF.
The Australia Telescope Compact Array is part of
the Australia Telescope which is funded by the Commonwealth of Australia for operation as a National
Facility managed by CSIRO. The Karl G. Jansky
Very Large Array (VLA). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
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Fig. 8. 1 GHz surface brightness-to-diameter diagram from Berezhko and Völk (2004), with G1.9+0.3
added. The evolutionary tracks are for ISM densities
of NH = 3, 0.3 and 0.003 cm−3 and explosion energies of ESN = 0.25, 1 and 3×1051 erg.
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and Völk 2004) superposed. G1.9+0.3 lies at (D, Σ)= (3.8 pc, 7.5 × 10−20 W m−2 Hz−1 Sr−1 ) in the diagram. Its position on the diagram tentatively suggests that it is in the mid-to-late free expansion phaseof evolution — expanding into a low density environment (nH . 0.3cm−3 ).

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RADIO-CONTINUUM EMISSION FROM THE YOUNG GALACTIC SNR G1.9+0.3

RADIO-KONTINUUM EMISIJA MLADOGGALAKTIQKOG OSTATKA SUPERNOVE G1.9+0.3
A. Y. De Horta1 , M. D. Filipović1 , E. J. Crawford1 , F. H. Stootman1 , T. G. Pannuti2 ,L. M. Bozzetto1 , J. D. Collier1 , E. R. Sommer1 and A. R. Kosakowski2
1

University of Western Sydney, Locked Bag 1797, Penrith South, DC, NSW 1797, Australia
E–mail: a.dehorta@uws.edu.au, m.filipovic@uws.edu.au, e.crawford@uws.edu.au2Space Science Center, Department of Earth and Space Sciences, Morehead State University,
235 Martindale Drive, Morehead, KY 40351 USA
E–mail: t.pannuti@moreheadstate.edu

UDK 524.354–77
Originalni nauqni rad
U ovoj studiji predstavǉamo nova
radio-kontinuum
posmatraǌa
teleskopom
ATCA na 6 cm najmlaeg ostatka supernovih(OS) u naxoj Galaksiji. Analizirana su i
sva dostupna ATCA i VLA posmatraǌa na ovoj
frekvenciji. Ostatak G1.9+0.3 je ∼181±25
godina star i godixǌa stopa rasta mu je
0.563%±0.078% u periodu izmeu 1984. i
1989. Primetili smo da se izmeu 1984. i
1989. ostatak xirio nexto sporije (0.484%
godixǌe) nego posle 1989., kada je ekspanzija

dostigla nivo od 0.641% godixǌe. G1.9+0.3
ima tipiqan radio-spektar za mlade ostatke
sa α =–0.72±0.26. G1.9+0.3 emituje proseqno 6% polarizovanog zraqeǌa na talasnoj
duini od 6 cm, sa maksimalnim intenzitetom
17%±3%. Ova polarizaciona emisija takoetesno prati rendgensko zraqeǌe. Proceǌeno
je priliqno jako magnetno poǉe u vrednosti od
273 µG xto predstavǉa jedno od najsnanijih
magnetnih poǉa u do sada posmatranim OS.

51