J/MNRAS/431/1107 M82 radio sources flux density variations (Gendre+, 2013)
Flux density variations of radio sources in M82 over the last three decades.
Gendre M.A., Fenech D.M., Beswick R.J., Muxlow T.W.B., Argo M.K.
<Mon. Not. R. Astron. Soc., 431, 1107-1120 (2013)>
=2013MNRAS.431.1107G 2013MNRAS.431.1107G
ADC_Keywords: Galaxies, nearby ; Radio sources
Keywords: galaxies: individual: M82 - galaxies: starburst -
radio continuum: galaxies
Abstract:
This paper presents the results of the 2009-2010 monitoring sessions
of the starburst galaxy M82, obtained with the Multi-Element
Radio-Linked Interferometer Network (MERLIN) at 5GHz and e-MERLIN at
6GHz. Combining several 5GHz MERLIN epochs to form a map with
33.0µJy/bm noise level, 52 discrete sources, mostly supernova
remnants and HII regions, are identified. These include three objects
which were not detected in the 2002 5GHz MERLIN monitoring session:
supernova SN2008iz, the transient source 43.78+59.3, and a new
supernova remnant shell. Flux density variations, in the long (1981 to
2010), medium (2002 to 2010) and short (2009 to 2010) term are
investigated. We find that flux densities of supernova remnants (SNRs)
in M82 stay constant in most of the sample (∼95 per cent), although
the distributions of flux density variations show an offset from zero.
This is consistent with a slight statistical reduction in flux density
of the source distribution. In addition, aside from SN2008iz and the
well-known variable source 41.95+57.5, two sources display tentative
evidence for short- and medium-term variations over the period
2009-2010. These sources are amongst the most compact SNR in M82.
These flux density variations could be due to changes in the
circumstellar and interstellar medium in which the shocks travel.
Description:
The 2009 monitoring campaign of M82 consisted of seven wide-field
MERLIN (Thomasson 1986) observations at a frequency of 4.994GHz,
observed between 2009 May and 2010 April. These were made using
parallel hands of circular polarization, and were correlated with a
total bandwidth of 16 MHz divided into 32 channels. Across all epochs
combined a total on-source integration time of 286.5h was used. Each
observing epoch was reduced and analysed individually and a deep
exposure map was produced by combining all of these data. In addition
to these, a single e-MERLIN observation was included in this study.
This observation was made in 2010 December as part of the e-MERLIN
commissioning programme and used a total bandwidth of 512MHz with a
median frequency of 6.26GHz. These data were correlated into four
individual sub-bands each divided into 512 frequency channels. These
e-MERLIN observations were observed prior the installation of the new
e-MERLIN wide-band IF system in spring 2011 and consequently only one
hand of polarization was used and the data displayed reduced
sensitivity in parts of the observing band.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 63 52 *Combined epoch (averaged over all 2009) normalized
(as described in Section 3.2) peak and integrated
flux densities, for all 52 detected objects
tablea1.dat 195 52 Normalized flux density (as described in Sect. 3.2)
for the 2002, 2005 and 2009-2010, MERLIN/e-MERLIN
monitoring sessions of M82
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Note on table2.dat: Sources previously identified in the literature as SNRs or
HII regions have been labelled accordingly. These identifications are taken
from Muxlow et al. (1994MNRAS.266..455M 1994MNRAS.266..455M), Wills et al. (1997MNRAS.291..517W 1997MNRAS.291..517W),
Allen (1999, PhD thesis, Univ. Toronto, Canada) and McDonald et al.
(2002MNRAS.334..912M 2002MNRAS.334..912M).
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See also:
J/MNRAS/391/1384 : Deep MERLIN 5GHz radio sources in M82 (Fenech+, 2008)
J/MNRAS/414/1329 : M82 X-ray sources long-term variability (Chiang+, 2011)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/52] Sequential number
4- 13 A10 --- Name Radio-source name (SS.ss+SS.ss, B1950) (1)
14 A1 --- n_Name [ab] Transient or previously undetected (2)
16- 17 I2 h RAh Right ascension (J2000)
19- 20 I2 min RAm Right ascension (J2000)
22- 26 F5.2 s RAs right ascension (J2000)
28 A1 --- DE- Declination sign (J2000)
29- 30 I2 deg DEd Declination (J2000)
32 -33 I2 arcmin DEm Declination (J2000)
35- 38 F4.1 arcsec DEs Declination (J2000)
40- 44 F5.2 mJy Sp Averaged peak flux density at 5GHz (mJy/beam);
the mean error is 0.01mJy.
46- 50 F5.2 mJy Si Integrated flux density at 5GHz
52- 55 F4.2 mJy e_Si rms uncertainty on Si
57- 63 A7 --- Com Comments on the type of source
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Note (1): Source name corresponds to the RAs, DEs values for B1950 coordinates
of source 09:55:00.000+69:40:00 (J2000).
Note (2): Note as follows:
a = SN2008iz (Brunthaler et al. 2009A&A...499L..17B 2009A&A...499L..17B) and transient source
43.78+59.3 (Muxlow et al. 2010MNRAS.404L.109M 2010MNRAS.404L.109M)
b = Source absent from the 2002 data with no previous reference found
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/52] Sequential number
4- 13 A10 --- Name Name (SS.ss+SS.ss, B1950)
15- 19 F5.2 mJy Sp09c 2009 combined 5GHz peak flux density (mJy/beam)
21- 25 F5.2 mJy Si09c 2009 combined 5GHz integrated flux density
27- 30 F4.2 mJy e_Si09c rms uncertainty on Si09c
32- 36 F5.2 mJy Sp09A ? 2009-05-01 5GHz peak flux density (mJy/beam)
38- 42 F5.2 mJy Si09A ? 2009-05-01 5GHz integrated flux density
44- 47 F4.2 mJy e_Si09A ? rms uncertainty on Si09A
49- 53 F5.2 mJy Sp09B ? 2009-05-26 5GHz peak flux density (mJy/beam)
55- 59 F5.2 mJy Si09B ? 2009-05-26 5GHz integrated flux density
61- 64 F4.2 mJy e_Si09B ? rms uncertainty on Si09B
66- 70 F5.2 mJy Sp09C 2009-07-28 5GHz peak flux density (mJy/beam)
72- 76 F5.2 mJy Si09C 2009-07-28 5GHz integrated flux density
78- 81 F4.2 mJy e_Si09C rms uncertainty on Si09C
83- 87 F5.2 mJy Sp09D ? 2009-08-19 5GHz peak flux density (mJy/beam)
89- 93 F5.2 mJy Si09D ? 2009-08-19 5GHz integrated flux density
95- 98 F4.2 mJy e_Si09D ? rms uncertainty on Si09D
100-104 F5.2 mJy Sp09E ? 2009-09-12 5GHz peak flux density (mJy/beam)
106-110 F5.2 mJy Si09E ? 2009-09-12 5GHz integrated flux density
112-115 F4.2 mJy e_Si09E ? rms uncertainty on Si09E
117-121 F5.2 mJy Sp09F ? 2009-09-25 5GHz peak flux density (mJy/beam)
123-127 F5.2 mJy Si09F ? 2009-09-25 5GHz integrated flux density
129-132 F4.2 mJy e_Si09F ? rms uncertainty on Si09F
134-138 F5.2 mJy Sp10A ? 2010-04-06 5GHz peak flux density (mJy/beam)
140-144 F5.2 mJy Si10A ? 2010-04-06 5GHz integrated flux density
146-149 F4.2 mJy e_Si10A ? rms uncertainty on Si10A
151-155 F5.2 mJy Sp10B ? 2010-12-17 5GHz peak flux density (mJy/beam)
157-161 F5.2 mJy Si10B ? 2010-12-17 5GHz integrated flux density
163-166 F4.2 mJy e_Si10B ? rms uncertainty on Si10B
168-172 F5.2 mJy Si02 ? 2002 5GHz integrated flux density (mJy/beam)
174-177 F4.2 mJy e_Si02 ? rms uncertainty on Si02
179-183 F5.2 mJy Si05 ? 2005 5GHz integrated flux density (mJy/beam)
185-188 F4.2 mJy e_Si05 ? rms uncertainty on Si05
190 A1 --- l_alpha Limit flag on alpha
191-195 F5.2 --- alpha ? Spectral index (3)
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Note (3): Spectral index information was retrieved from McDonald et al.
(2002MNRAS.334..912M 2002MNRAS.334..912M). When unavailable, standard values of α=-0.7 for
SNR and α=0.0 for HII regions were assumed. The 2010 6GHz e-MERLIN data
were converted to 5GHz using the relation Sν∝να.
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History:
* 27-Jun-2014: From electronic version of the journal
* 27-Jul-2015: Complete positions added
(End) Patricia Vannier [CDS] 23-May-2014