TITLE: GCN CIRCULAR NUMBER: 17784 SUBJECT: GRB 150413A: CrAO optical observations DATE: 15/04/28 19:47:55 GMT FROM: Alexei Pozanenko at IKI, Moscow V. Rumyantsev (CrAO), K. Antoniuk (CrAO), E. Mazaeva (IKI), 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) with AZT-11 telescope of CrAO observatory starting on Apr. 13 (UT) 17:39:02. Several images were take in R-filter. The afterglow (Ivanov et al., GCN 17689) is clearly detected in all single images of 180 s exposure. Preliminary photometry is following Date, UT start, OT, OT_err 2015-04-13 17 40 32.11 16.56 0.12 2015-04-13 17 43 36.17 16.97 0.30 2015-04-13 17 46 40.21 16.48 0.07 2015-04-13 17 49 44.26 16.73 0.11 2015-04-13 17 52 48.30 16.48 0.15 2015-04-13 17 55 52.37 16.62 0.13 2015-04-13 17 58 56.41 16.74 0.09 2015-04-13 18 02 00.58 16.63 0.13 2015-04-13 18 05 04.68 16.78 0.10 2015-04-13 18 08 08.76 16.77 0.09 2015-04-13 18 11 12.83 16.63 0.07 2015-04-13 18 14 16.87 16.74 0.06 2015-04-13 18 17 20.95 16.74 0.04 2015-04-13 18 20 25.30 16.76 0.06 2015-04-13 18 23 29.10 16.77 0.10 2015-04-13 18 26 33.15 16.90 0.08 2015-04-13 18 29 37.20 16.74 0.07 2015-04-13 18 32 41.25 16.71 0.05 2015-04-13 18 35 45.30 16.78 0.04 2015-04-13 18 38 49.36 16.77 0.03 2015-04-13 18 44 31.44 16.88 0.03 2015-04-13 18 47 35.48 16.81 0.03 2015-04-13 18 50 39.57 16.87 0.03 2015-04-13 18 53 43.66 16.92 0.03 2015-04-13 18 56 47.73 16.98 0.03 2015-04-13 18 59 51.90 17.02 0.03 2015-04-13 19 02 55.98 16.95 0.04 2015-04-13 19 06 00.64 16.94 0.04 2015-04-13 19 09 04.22 17.08 0.07 2015-04-13 19 12 08.35 17.05 0.06 The photometry is based on nearby USNO-B1.0 1618-0098185 (Xu et al., GCN 17693) assuming R=15.59.