{
  "bibcode": "1999GCN...287....1T",
  "body": "G. B. Taylor (NRAO), D. A. Frail (NRAO), and S. R. Kulkarni (Caltech) \nreport:\n\n\"On 1999 March 10.01 we carried out VLBA observations of the radio\nsource, J0342+1709, claimed to be a possible afterglow candidate for\nGRB 981220 based on early observations at WSRT (GCN #168) and the VLA\n(GCN #170).  Within the 0.9\" x 0.9\" error box set by VLA observations\nat 8.4 GHz we detect an extended source with a peak flux density at 5\nGHz of 404 +/- 60 microJy.  The position of the radio source is\nra=03h42m28.9611s dec=17d09'14.669\" (equinox J2000) with an\nuncertainty of 0.05 arcsec in each coordinate.  The integrated flux\ndensity of this source is 528 +/- 90 microJy.  The flux density at 5\nGHz measured by the VLA on March 8.96 was 510 +/- 26 microJy.  The\nVLBA image can be viewed at http://www.nrao.edu/~gtaylor/G981220.html.\n\nThe standard models and redshift distribution of GRB afterglows\npredict that the radio counterpart to G981220 should be unresolved by\nour VLBA observations.  The \"core-jet\" morphology of the VLBA image\ntherefore makes it unlikely that J0342+1709 is associated with\nG981220.  A more plausible explanation is that it is a highly variable\nbackground intraday-variable (IDV) source.  Such sources are known to\nvary on timescales of days to weeks, and consist of a strong core and\none-sided jet.  This explanation is supported by the location of\nJ0342+1709 outside of the refined IPN localization (GCN #270) for\nG981220.\"\n\nThis message is citeable.",
  "circularId": 287,
  "createdOn": 922832311000,
  "email": "gtaylor@aoc.nrao.edu",
  "subject": "GRB981220 VLBA observations",
  "submitter": "Greg Taylor at NRAO  <gtaylor@aoc.nrao.edu>",
  "eventId": "GRB 981220"
}