TITLE: GCN CIRCULAR NUMBER: 11266 SUBJECT: GRB 100901A: optical observation in Maidanak, break confirmation DATE: 10/09/10 01:48:03 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Volnova (SAI MSU), A. Pozanenko (IKI), M. Ibrahimov (MAO), B. Hafizov (MAO), B. Satovski (Astrotel) report on behalf of larger GRB follow-up collaboration: We observed the field of the Swift GRB 100901A (Immler et al., GCN 11159) with AZT-22 telescope of Maidanak observatory starting Sep. 7 (UT) 20:32:06. We clearly detect the afterglow (Immler et al., GCN 11159 and other follow-up ground based observations) in R-filter. The photometry of a stacked image is based on the same reference SDSS-DR7 stars used by our collaboration previously (GCNs 11191, 11200, 11255): T0+ Filter, Exposure, mag. (mid, d) (s) 6.2977 R 4*300 22.05+/-0.09 The photometry above confirms suggested break (Kann et al, GCN 11246) in a light curve of the afterglow.