{
  "bibcode": "2002GCN..1555....1B",
  "body": "E. Berger, S. R. Kulkarni, D. A. Frail, A. Soderberg, P. A. Price, D. W.\nFox, F. A. Harrison, and S. Yost report on behalf of the larger\nCaltech-NRAO-CARA GRB collaboration:\n\nFollowing the discovery of the optical transient of GRB 020903 (GCN #1530)\nby Soderberg et al. (GCN #1554), we observed the position of the OT with\nthe VLA on Sep. 27.22 UT.  We detect a bright radio source at the position\nof the OT, with a flux of 1.1 mJy at 8.46 GHz.  The source is not detected\nin the NRAO VLA Sky Survey (NVSS; Condon et al. 1998, AJ, 115, 1693) above\ntheir flux limit of 1 mJy at 1.4 GHz.  Observations undertaken today (Sep.\n29.11 UT) show that the source is fading with a flux of 0.7 mJy at 8.46\nGHz.\n\nThe variable radio counterpart lends supports to the identification of the\noptical transient (OT) reported by Soderberg et al. as the afterglow of\nXRF 020903.  Unlike the optical emission, the radio emission is dominated\nby the afterglow.\n\nThe isotropic, prompt energy release of XRF 020903 (using the redshift of\nz=0.25, GCN #1554, and a rough estimate of the fluence detected by WXM;\nsee the HETE-2 web page: http://space.mit.edu/HETE/Bursts/GRB020903/) is\nwell below those of typical cosmological GRBs but higher than that of GRB\n980425.  Therefore, the energy in relativistic ejecta of XRF 020903 is\nintermediate between that of SN1998bw, about 10^49 erg, as inferred from\nthe radio emission (Kulkarni et al. 1998, Nature, 395, 663), and that of\ntypical cosmological GRBs.  Finally, the ratio of energy in the\nrelativistic ejecta to the energy in the SN of XRF 020903 is well below\nthose of cosmological GRBs (typically 1-10), but higher than SN1998bw\n(~0.01). These arguments suggest that XRF 020903 is a \"transition\" object\n-- a link between GRB 980425 and comsological GRBs.\n\nScaling the ratio of radio to X-ray luminosity of SN1998bw to XRF 020903,\nwe predict detectable X-ray emission on this timescale, which may be an\nadditional robust indicator of the relativistic energy in the ejecta.\n\nSee http://www.astro.caltech.edu/~ams/XrF.html for a full discussion.",
  "circularId": 1555,
  "createdOn": 1033280550000,
  "email": "ejb@astro.caltech.edu",
  "subject": "Radio Observations of XRF 020903: The Missing Link",
  "submitter": "Edo Berger at Caltech  <ejb@astro.caltech.edu>"
}