TITLE: GCN CIRCULAR NUMBER: 19929 SUBJECT: GRB 160917A: Mondy optical observations DATE: 16/09/17 21:11:04 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Volnova (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), E. Mazaeva (IKI), I. Korobtsev (ISTP) report on behalf of larger GRB follow-up collaboration: We observed the field of the GRB 160917A (Racusin et al. GCN 19926) with AZT-33IK telescope of Sayan observatory (Mondy) starting on Sep., 17 (UT) 14:30:30. We obtained several images in R-filter. We detected the optical source within enhanced XRT error circle (Evans et al., GCN 19927) in coordinates (J2000) 19 42 39.81 +46 24 12.1 with uncertainities of 0.4 arcsec in both coordinates. Preliminary photometry of the afterglow is following Date UT start t-T0 Filter Exp. OT UL (3 sigma) (mid, days) (s) 2016-09-17 14:30:30 0.14601 R 120*30 20.60 +/- 0.20 22.9 Photometry is based on nearby USNO-B1.0 stars ID RA Dec R2 1 1363-0324591 19:42:38.95 +46:23:53.8 16.62 2 1364-0326339 19:42:40.68 +46:24:37.0 17.40 3 1363-0324630 19:42:42.78 +46:23:28.7 17.05 We suggest the source as optical afterglow of GRB 160917A. The finding chart can be found at http://grb.rssi.ru/GRB160917A/160917A_Mondy_fc.png