TITLE: GCN CIRCULAR NUMBER: 11366 SUBJECT: GRB 101023A: Gemini discovery of optical afterglow DATE: 10/10/24 03:00:08 GMT FROM: Andrew Levan at U.of Leicester A.J.Levan (U. Warwick), D. Perley (U. Berkeley) and P. D'Avanzo (INAF-OAB) report for a larger collaboration: "We observed the field of GRB 101023A (Saxton et al. GCN 11363) with GMOS on Gemini-South. We obtained a first epoch of observations in the r-band beginning at 24 October 00:38, approximately 1.8 hours post-burst. A second epoch was obtained at 01:26. In these two observations we identify a fading point source at a location of RA(J2000) 21:11:51.24 DEC(J2000) -65:23:15.84 We identify this as the afterglow of GRB 101023A. The afterglow fades by approximately 0.35 magnitudes between the two epochs of observation, and has r~20.5 in our first epoch (based on archival zeropoints). The afterglow position is ~2.8" from the refined XRT position of Osborne et al. (GCN 11365). We thank the staff of Gemini, in particular Henry Lee, for their help with these observations."