TITLE: GCN CIRCULAR NUMBER: 11168 SUBJECT: GRB 100901A: optical observation at Mt.Terskol DATE: 10/09/01 23:22:35 GMT FROM: Alexei Pozanenko at IKI, Moscow M. Andreev, A. Sergeev (Terskol Branch of Institute of Astronomy) and A. Pozanenko (IKI) on behalf of larger GRB follow up collaboration report: We are continuing observations of the Swift GRB 100901A (Immler et al., GCN 11159) with the Z-600 telescope of Mt.Terskol observatory in R-filter (Andreev et al., GCN 11166). In a combined image at mid time Sep. 01 (UT) 20:09 we still detect bright afterglow (Immler et al., GCN 11159; Guidorzi et al., GCN 11160; Ivanov et al., GCN 11161; Klunko et al., GCN 11162). Preliminary photometry is based on the reference star USNO-B1.0 #1127-0027231 RA(J2000) = 01 49 06.78 Dec(J2000) = +22 47 03.3 assuming R=15.37: T0+ Filter, Exposure, OT (d) (s) 0.2742 R 5x60 17.05 +/-0.02