TITLE: GCN GRB OBSERVATION REPORT NUMBER: 319 SUBJECT: GRB 990510, BVI photometry DATE: 99/05/12 12:47:54 GMT FROM: Andrzej Udalski at Warsaw U. Observatory G. Pietrzynski and A. Udalski (Warsaw University Observatory) report on behalf of the OGLE microlensing survey team: Observations of the optical counterpart of GRB 990510 collected with the 1.3-m Warsaw telescope at the Las Campanas Observatory (Chile) on May 11/12, 1999 indicate that the object faded smoothly to V=21.2 and I=20.3 on May 12.4 UT. Single observation in the B-band collected on May 11.3607 UT yields the following colors of the GRB990510 counterpart: B=20.47+/-0.05, B-V=0.54+/-0.06 and V-I=0.88+/-0.04. This indicates significantely different spectral distribution as compared to regular stars. The nearby galaxy, mentioned by Kaluzny et al 1999 GCN #314, is clearly visible on collected frames. Updated photometry of the optical counterpart of GRB 990510 and light curves are available from the OGLE Internet archive: http://www.astrouw.edu.pl/~ftp/ogle [GCN OP NOTE (12May99): Due to a problem in processing this Circular, the NUMBER was erroneously assigned to be 318, when in fact it should have been 319. The archive copies have been fixed.]