TITLE: GCN CIRCULAR NUMBER: 18416 SUBJECT: GRB 151006A: Mondy optical upper limit DATE: 15/10/11 10:03:30 GMT FROM: Alexei Pozanenko at IKI, Moscow E. Mazaeva (IKI), E. Klunko (ISTP), A. Volnova (IKI), I. Korobtsev (ISTP), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of Swift GRB 151006A (Kocevski et al., GCN 18398) with AZT-33IK telescope of Sayan observatory (Mondy) starting on Oct. 18 (UT) 16:50:47. We obtained several images in R-filter of 120 s exposure. Within XRT error circle (Goad et al., GCN 18403) we do not detect any optical source. Upper limit is following Date UT start t-T0 Filter Exp. UL (3 sigma) (mid, days) (s) 2015-10-06 16:50:47 0.31306 R 35*120 22.4 Photometry is based on USNO-B1.0 stars: USNO-B1.0_id R2 1604-0085829 18.23 1604-0085812 16.90