{
  "bibcode": "1999GCN...314....1K",
  "body": "J. Kaluzny (Warsaw Univ. Obs.), P. M. Garnavich, K. Z. Stanek\n(Harvard-Smithsonian CfA), W. Pych (Warsaw Univ. Obs.) and I. Thompson\n(Carnegie Obs.) report:\n\nWe measured the object at RA 13:38:07.64, Decl -80:29:48.8 (J2000)\n(coordinates based on the GSC catalog), reported by Vreeswijk et\nal. (GCN 310) to be a possible optical counterpart to GRB 990510 in\nour R-band images taken with the 1.0-meter Swope telescope at the Las\nCampanas Obs.  We find that the object declined by 0.34 mag over 4.6\nhours beginning May 10.995 (UT) in the R-band.  The data is consistent\nwith a power-law decline with decay index of 0.89, obtained by fitting\ncombined data of Galama et al. (GCN 313) and ours.  The comparison\nstar (end figures of 00.82, 11.7) assumed by Galama et al. to be\nR=17.2 is actually given in the USNO A2.0 catalog as R=16.5. We find\nthe R magnitudes in this region of the USNO catalog to be of dubious\nquality, especially fainter than 16.5.  It is important to obtain an\nindependent photometric calibration for this field.\n\nAdding seven 300s exposures in R with approximately 1\" seeing reveals\nan object 1.8\" south of the OT and about 3 magnitudes fainter which\nmay be the host galaxy.\n\nCompared to nearby field stars, the OT appears significantly\nbluer by approximately 0.4 mag in V-R color.\n\nThe R-band lightcurve and the combined image of the field are\navailable at http://cfa-www.harvard.edu/~peterg/grb.html.\n\nThis message is citeable.",
  "circularId": 314,
  "createdOn": 926400712000,
  "email": "kstanek@cfa.harvard.edu",
  "subject": "GRB 990510 optical observations",
  "submitter": "Krzysztof Z. Stanek at CfA  <kstanek@cfa.harvard.edu>",
  "eventId": "GRB 990510"
}