TITLE: GCN CIRCULAR NUMBER: 18635 SUBJECT: GRB 151027A: Maidanak optical observations DATE: 15/11/22 21:48:09 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Pozanenko (IKI), E. Mazaeva (IKI), A. Volnova (IKI), O. Burhonov (UBAI) report on behalf of larger GRB follow-up collaboration: We observed the Swift GRB 151027A (Maselli et al., GCN 18478) with AZT-22 telescope of Maidanak observatory equipped with SNUCAM in R filter. We obtained several images in R-filter on Oct., 30, Nov., 6 and Nov., 9 under mean FWHM of about 0.9". The afterglow (Maselli et al., GCN 18478; Zheng and Filippenko, GCN 18479) is clearly detected in each epoch. The afterglow is well separated from nearby source (Dichiara et al.GCN 18510; Mazaeva et al., GCN 18559). Preliminary photometry of the afterglow is following Date UT start t-T0 Filter Exp. OT Err. (mid, days) (s) 2015-11-06 15:04:07 10.474 R 10*300 23.30 0.24 2015-11-09 14:06:04 13.443 R 10*300 23.33 0.20 The photometry is based on nearby USNO-B1.0 stars USNO-B.1_id R2 1513-0237223 16.66 1513-0237251 16.81 1513-0237270 16.78 A preliminary light curve of the afterglow can be found in http://grb.rssi.ru/GRB151027A/GRB151027A_lc.png At this time it is unclear what is a reason of flattening of the light curve at 11-13 days. It might be SN signature or it is continuing bumps of the light curve previously seen at least on ~ 1.3 days and ~3 days.