{
  "bibcode": "2005GCN..3083....1F",
  "body": "Derek B. Fox and S. Bradley Cenko report on behalf of the\nCaltech-NRAO-Carnegie GRB collaboration:\n\n\"Examination of a coadded R-band image from our P60 observations for\nthe BAT localization region of GRB050309 (Barthelmy et al, GCN 3082),\ntaken at a mean epoch of 10:55 UT (12 minutes after the burst),\nconfirms our earlier report (Cenko & Fox, GCN 3080) of the absence of\nnew optical sources to the limit of the Digitized Sky Survey and our\nown observations.  We estimate this limit to be R < 20.5 mag as\ncalibrated against the USNO B-1.0 catalog magnitudes of bright stars\nin the region.\n\nThis limit applies to XRT source #2 (GCN 3082), where no emission is\nseen.  The position of XRT source #1 is 6-arcsec (twice the FWHM in\nour images) from a bright star and USNO B-1.0 catalog object having\nR=12.98 mag.  No extension of the catalog star is apparent in our\nimages.\"",
  "circularId": 3083,
  "createdOn": 1110437384000,
  "email": "derekfox@astro.caltech.edu",
  "subject": "GRB050309: Early optical limit from P60",
  "submitter": "Derek Fox at CIT  <derekfox@astro.caltech.edu>",
  "eventId": "GRB 050309"
}