GCN Circular 3829
Derek B. Fox (Penn State) and S. Bradley Cenko (Caltech) report on behalf of a larger collaboration: "We have observed the BAT/XRT localization region of GRB050820 (Swift Trigger #151207) with the robotic Palomar 60-inch telescope (P60), in a series of automated exposures beginning at 06:37 UT, approximately 3 minutes after the burst. We identify a bright, new, variable point source within the XRT (and BAT) localization region at coordinates: R.A. 22:29:38.11, Dec +19:33:37.1 (J2000) with coordinate uncertainty <0.5 arcsec relative to USNO-B1.0 catalog astrometry. Photometry of the source relative to the USNO-B1.0 catalog indicates that in the R-band it brightens to a peak magnitude of R~14.7 mag at 7 minutes after the burst and has decayed by 0.4 mag at 12 minutes after the burst. We therefore identify the source as the optical afterglow of GRB050820."