{
  "bibcode": "2002GCN..1434....1D",
  "body": "Fading Optical Source in the Field of GRB020531\n\nA. Dullighan, G. Monnelly, N. Butler, R. Vanderspek, P. Ford, G.\nRicker (MIT); H. Ebeling, R. Wainscoat (U. Hawaii);\nN. Kawai, A. Yoshida (RIKEN, Japan)\n\nwrite:\n\nWe have observed the error box of the short-hard burst source\nGRB020531 (GCN #1399, #1402) with the Baade 6.5m telescope\nat the Magellan Observatory on June 1.16 and June 10.13 UT,\nand with the Subaru 8.2m telescope at Mauna Kea Observatory\non June 5.43 UT. The R band images were calibrated using the\ndata provided by Henden et al.(GCN #1422). Our observations\nwere as follows:\n\n2002 Date\tInstrument,\t   Exposure Time    Limiting R Mag.\n    UT\t\t  Telescope\t\t(sec)\t      (3 sigma)\n\nJune 1.16\tLDSS2, Baade\t    \t180 \t\t23.6\nJune 5.43\tSuprimeCam, Subaru\t420 \t\t25.5\nJune 10.13\tLDSS2, Baade\t    \t360 x 2\t   \t24.0\n\nWe detect a fading optical counterpart for Chandra Source #5\n(GCN #1415) in all three epochs.\n\n2002 Date\t\tR Mag\t\tError\n    UT\t\t\tof #5\n\nJune 1.16\t\t23.12\t\t0.20\nJune 5.43\t\t23.79\t\t0.06\nJune 10.13\t\t23.96\t\t0.20\n\nThe decline in brightness of the counterpart between the measurements\nis consistent with a power law decay with alpha = 0.35 +/- 0.05.\n\nThe relative X-ray brightness of Chandra Source #5 at the two\nepochs of the Chandra observations is consistent with the optical\ndecay index. However, the independent significance of any X-ray\ndecline is low (1.4 sigma level-of-confidence).\n\nSince Source #5 lies just outside the current error box for GRB020531\n(GCN #1407), its possible association, if any, with GRB020531\nis unclear.\n\nThis message may be cited.",
  "circularId": 1434,
  "createdOn": 1024541375000,
  "email": "grr@space.mit.edu",
  "subject": "Fading Optical Source in the Field of GRB020531",
  "submitter": "George Ricker at MIT  <grr@space.mit.edu>",
  "eventId": "GRB 020531"
}