{
  "bibcode": "2003GCN..1907....1S",
  "body": "A. M. Soderberg, D. Fox, S. Kulkarni, and E. Berger (Caltech) report on\nbehalf of a larger GRB collaboration:\n\n\"We have imaged the field of GRB 030227 with ESI on Keck II beginning\nat Feb 28.242 UT in various optical bands.  In the R-band image, we\nfind two sources in the 3-arcminute (radius) error circle of the XMM\nsource 'S1' (Loiseau et al. GCN 1901), hereafter S1-A and S1-B:\n\n    'S1-A' 04:57:33.05 +20:29:04.9 (J2000)\n    'S1-B' 04:57:32.80 +20:29:06.2 (J2000)\n\nThe positions are accurate to 0.3\" and are based on 19 stars from the\nGSC-II catalog.\n\nThe source S1-A is clearly seen in the Isaac Newton Telescope (INT)\nR-band image presented by Castro-Tirado et al. (GCN 1904).  We find a\nmagnitude of R ~ 23.5 for S1-A and R ~ 25.0 for S1-B relative to the\nabove set of GSC-II stars.  Comparison with Castro-Tirado et al. (GCN\n1904) indicates that the source has faded by ~1.0 magnitudes since\nFeb. 27.872 UT.  This fading is visually confirmed by comparing our\nimage (see URL below) with the INT image.  We note that the candidate\nof Ofek and Gal-Yam (GCN 1903) may also be fading; with the same\ncalibration we measure R ~ 22.1 for their source and R ~ 18.1 for\ntheir star A.\n\nGiven the coincidence of S1-A with the X-ray source and its fading\nbehavior we suggest that it is the optical afterglow of GRB 030227.\n\nOur image can be found at:\n\n\thttp://www.astro.caltech.edu/~ams/grb030227/\n\nAnalysis of other candidates is in progress.\"",
  "circularId": 1907,
  "createdOn": 1046426537000,
  "email": "ams@astro.caltech.edu",
  "subject": "GRB 030227: fading of candidate optical afterglow 'S1-A'",
  "submitter": "Alicia Soderberg at Caltech  <ams@astro.caltech.edu>",
  "eventId": "GRB 030227"
}