TITLE: GCN CIRCULAR NUMBER: 11152 SUBJECT: GRB 100823A: optical observations DATE: 10/08/27 20:23:43 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Pozanenko (IKI), A. Volnova (SAI MSU), B. Satovski (Astrotel), M. Ibrahimov (MAO) report on behalf of larger GRB follow-up collaboration: We observed the field of the Swift GRB 100823A (Mangano et al. GCN 11135) with AZT-22 telescope of Maidanak observatory. Several images in I-filter were obtained starting on Aug. 23 (UT) 20:47:02. We do not detect the object C (Levan et al. GCN 11145; Suzuki et al. GCN 11146) up to I=22.2m. We clearly detect both objects A and B (Levan et al. GCN 11138). The photometry of stacked image is based on USNO-B1.0 star 0958-0013520 located at RA(J2000) = 01:22:45.50, DEC(J2000) = +05:49:03.0 and used as reference star in GCN 11140 (Guziy et al). Object, t-T0, Filter, Exposure, OT, Upper limit (3 sigma) (mid, d) (s) A 0.16605 I 19*180 21.06+/-0.09 22.2 B 0.16605 I 19*180 20.60+/-0.06 22.2 The photometry of the object A is compatible with photometry reported in GCN 11146 (Suzuki et al). Using photometry of the object C starting 5 minutes after burst (Suzuki et al. GCN 11146) and upper limit I=22.2m at 0.16605 days one can estimate power law decay index alpha > 1.25. We thank Otabek Burhonov for performing the observations and for his support.