TITLE: GCN CIRCULAR NUMBER: 13761 SUBJECT: GRB 120907A: optical observations of ISON-Kislovodsk DATE: 12/09/13 18:53:47 GMT FROM: Alexei Pozanenko at IKI, Moscow V. Nevski (ISON-Kislovodsk Observatory), A. Volnova (SAI MSU/IKI), I. Molotov (KIAM), A. Pozanenko (IKI) report on behalf of larger collaboration: We observed the field of GRB 120907A (Racusin et al., GCN 13716) with Santel-400AN (0.4-m f/3) telescope Ïf ISON-Kislovodsk observatory starting on Sep. 07 (UT) 00:34:32, i.e. ~10.2 minutes after burst trigger. We took several unfiltered images of 30 s and 60 s exposures. In a stacked images we clearly detect optical afterglow of GRB 120907A (Racusin et al., GCN 13716; Gorbovskoy et al., GCN 13718; Kruehler et al., GCN 13719). A preliminary photometry of stacked frames is based on the USNO-B1.0 (R2) nearby stars: T_start, T0+, Exp, Filter, OT (UT) mid (d) (s) 00:34:32 0.00899 10x30 none 18.55+/-0.09 00:51:45 0.02120 5x60 none 18.95+/-0.13 00:58:09 0.02980 8x60 none 19.52+/-0.20 01:16:32 0.04339 8x60 none 19.50+/-0.20