TITLE: GCN CIRCULAR NUMBER: 12333 SUBJECT: GRB 110731A: SAO RAS and Terskol observations DATE: 11/09/09 08:30:16 GMT FROM: Vladimir Sokolov at SAO RAS A. S. Moskvitin, V. V. Sokolov, O. I. Spiridonova (SAO RAS, Russia), M. V. Andreev, A. V. Sergeev, N. A. Parakhin (Terskol Branch of Institute of Astronomy, Russia) We observed the field of GRB 110731A (Oates et al., GCN 12215) on July, 31 with 0.6-m Zeiss-600 (Terskol Branch of Institute of Astronomy, Russia) equipped with the PixelVision Vienna CCD (1024 x 1024, bin 2 x 2) + R filter, and 1-m Zeiss-1000 (SAO RAS, Russia) equipped with the E2V 42-40 CCD (2048 x 2048, bin 2 x 2) + B and Rc filters. In both cases the observations carried out at a high airmass and with the seeing ~4". At all stacked images we did not detect any source within the Swift/UVOT error circle (Oates., GCN 12222). Close to the error circle are visible two objects which are also present in the USNO-B.1 catalogue: S1: USNO-B.1 0614-0802286 (R.A.=18:42:00.72, Dec.=-28:32:14.9, E.=2000.0) & S2: USNO-B.1 0614-0802328 (R.A.=18:42:01.24, Dec.=-28:32:11.6, E.=2000.0). Our astrometric calibration and photometry of S1 object showed that it can contain flux from OT but due to large seeing we can not distinguish bright S1 and faint OT. All three co-added images are shown at ftp://ftp.sao.ru/pub/grb/GRB110731A/GRB110731A.jpg Upper limits are shown at the following table. _________________________________________________________ mid. time, UT filter exp., sec 3-sigma lim. telescope _________________________________________________________ 19:15 R 53 x 200 19.9 Zeiss-600 19:24 Rc 31 x 60 21.7 Zeiss-1000 19:38 B 22 x 60 20.8 Zeiss-1000 _________________________________________________________ We use USNO-B.1 star 0614-0802353 (R.A.=18:42:01.83, Dec.-28:32:23.9, E.=2000.0, B2 = 15.77, R2 = 14.29) as a standard, and did not apply Galaxy extinction correction. This message can be cited.