{
  "bibcode": "2001GCN..1156....1S",
  "body": "R. Subrahmanyan, Australia Telescope National Facility,\nS. R. Kulkarni & E. Berger, California Institute of Technology, and \nD. A. Frail, National Radio Astronomy Observatory report \non behalf of a larger collaboration:\n\n\"We imaged the error circle of GRB 011121 (GCN 1147, 1148) with the\nAustralia Telescope Compact Array (ATCA), Narrabri, Australia. The\nobservations were conducted in the 3-cm band.  The observations started\nat UT 1600, November 22 2001 and lasted 12 hours.\n\nThe rms of the combined 8640 & 8768 MHz image is 35 microJy and the\nbeam is 1.37x1.21 arcsec (PA=-27 deg).  Only one source is detected in\nthe general vicinity of the optical transient (OT) reported by\nWyrzkyowski et al. (GCN 1150).  This source, hereafter\nATCA 113429.6-760141, is is located at 11h 34m 29.63s -76d 01m 41.5s\n(J2000, uncertainty of about 0.2 arcsec).  It has a peak flux of 0.2\nmJy and is embedded in some radio nebulosity; the integrated flux is\n0.25 mJy. \n\nThe discrepancy between the position of ATCA 113429.6-760141 and the\nposition of the optical transient (GCN 1150) motivated us to\nreinvestigate the optical/IR astrometry. As reported in GCN 1155, the\ncoordinates of the OT as given in GCN 1150 are likely to be in error\nand that the true position of the OT/NIRT is, within errors, the same\nas that of ATCA 113429.6-760141.  We conclude that ATCA 113429.6-760141\nis the radio afterglow of GRB 011121. \n\nSeparately, we note that the radio frame does not suffer from zonal\nerrors. In contrast, GSC suffers from such errors (and USNO less so).\nThus the position of ATCA 113429.6-760141 is quite secure and\nwith additional observations the source will be located to an accuracy\nbetter than the usual radio-optical frame tie.\n\nThe 2-arcsec nebulosity is likely the radio host galaxy of GRB 011121.\nIf so, assuming that the nebulosity is 0.05 mJy (a lower limit; we\ncould be missing some extended flux) and a typical spectral index of\n-0.5 (between 1.4 and 8.5 GHz) we obtain Star Formation Rate (SFR, M>5\nsolar masses; Salpeter IMF) of 13 solar masses per year or SFR(M > 0.1\nMsun) of 70 solar masses per year. \n\nWe encourage deep optical/IR imaging to fully reveal the extent\nof the presumed host galaxy.\"",
  "circularId": 1156,
  "createdOn": 1006560546000,
  "email": "srk@astro.caltech.edu",
  "subject": "GRB 011121: Radio Observations",
  "submitter": "Shri Kulkarni at Caltech  <srk@astro.caltech.edu>",
  "eventId": "GRB 011121"
}