TITLE: GCN CIRCULAR NUMBER: 17692 SUBJECT: GRB 150413A: Khureltogot optical observations DATE: 15/04/13 15:55:04 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Schmalz (AIP), A. Pozanenko (IKI), N. Tungalag (Research Center of Astronomy and Geophysics MAS), E. Mazaeva (IKI), A. Volnova (IKI), I.Molotov (KIAM), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the GRB 150413A (Markwardt et al., GCN 17688; Serino et al., GCN 17691) with ORI-40 telescope of Khureltogot observatory starting on Apr., 13 (UT) 14:08:52, i.e. ~10 minutes after burst trigger. Within BAT/Swift error circle we clearly detect fading optical source (Ivanov et al. GCN 17689, Tyurina et al. GCN 17690). Preliminary photometry of the source in single images is following Date UT start t-T0 Filter Exp. OT OT_err (mid, days) (s) 2015-04-13 14:08:52 0.0069 none 60 14.7 0.1 2015-04-13 14:39:52 0.0318 none 60 15.6 0.1 2015-04-13 15:11:54 0.0541 none 60 16.3 0.1 Photometry is based on nearby USNO-B1.0 stars, R2 mags. Observation is continuing.