TITLE: GCN CIRCULAR NUMBER: 12290 SUBJECT: GRB 110820A: CrAO optical upper limit DATE: 11/08/20 22:17:57 GMT FROM: Alexei Pozanenko at IKI, Moscow V. Rumyantsev, K. Antoniuk (CrAO), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the Swift GRB 110820A (Troja et al., GCN 12288) with AZT-11 telescope of CrAO between Aug. 20 (UT) 18:23 - 19:21. Within the XRT error box (Troja et al., GCN 12288) we do not detect any source. The photometry is based on the USNO B1.0 star 1602-0161058 (22:52:45.06 +70:17:17.5) assuming R=18.23: T0+ Filter, Exposure, OT, Upper Limit (3 sigma) (mid, d) (s) 0.0520 R 20x180 n/d 21.6