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GCN Circular 2483

GRB 031203: Variable Radio Source
2003-12-08T06:47:38Z (21 years ago)
Alicia Soderberg at Caltech <>
A. M. Soderberg, S. R. Kulkarni (Caltech) and D. A. Frail (NRAO) report
on behalf of a larger collaboration:

"On 2004 Dec. 7.52 UT we carried out further VLA observations at
 8.5 GHz of the radio source reported earlier (GCN 2473) and which
 lies within the 6-arcsecond error circle of the XMM source S1 (GCN
 2464).  The source flux density has decreased by a factor of two
 since our last report. Given that S1 is also fading (GCN 2477) we
 conclude that likely the radio source is the afterglow of GRB
 0312103 (GCN 2459).

 As noted by Bloom et al. (GCN 2481) and Prochaska et al. (GCN
 2482) a galaxy at a redshift of 0.105 is coincident with the radio
 source.  Owing to the large zenith angle of the source the reported
 radio source position may suffer from larger than normal astrometric
 error (which will be improved by future observations). The radio
 source and the putative host galaxy can be considered to coincident
 within the true astrometric error.

 The isotropic energy release (assuming redshift of 0.105) in the
 20-200 keV band is about 9E49 erg (using the data from GCN 2460). The
 isotropic X-ray luminosity extrapolated to 10 hr (using data from
 GCN 2477) is about 5E43 erg/s. These are lower than normal releases
 and luminosities (see Berger, Kulkarni and Frail 2003) and the
 apparent early fading in the radio are consistent with GRB 031203
 being an abnormally low luminosity GRB. This GRB may bridge GRB
 980425 (at z=0.0085) associated with SN 1998bw and cosmological
 GRBs (typically z of 0.3 to 1). Further low frequency observations
 will settle the issue of total calorimetry.  The search for an
 underlying SN is worth trying, though obscuration within and outside
 our Galaxy may prove to be vexing."
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