TITLE: GCN CIRCULAR NUMBER: 18189 SUBJECT: GRB 150818A: continued Mondy optical observations DATE: 15/08/21 15:39:24 GMT FROM: Alexei Pozanenko at IKI, Moscow E. Mazaeva (IKI), E. Klunko (ISTP), A. Volnova (IKI), I. Korobtsev (ISTP), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We continue observations of the of Swift GRB 150818A (D'Elia et al., GCNC 18152) with AZT-33IK telescope of Sayan observatory (Mondy). We obtained several images in R-filter starting on Aug., 20 (UT) 16:54:32. The optical transient (Marshall et al., GCN 18155; McCauley et al., GCN 18161; Schulze et al., GCN 18164; Mazaeva et al., GCN 18175) is clearly visible. Preliminary photometry of the optical transient is following Date UT start t-T0 Filter Exp. OT Err. (mid, days) (s) 2015-08-20 16:54:32 2.23334 R 15*120 21.15 0.09 Photometry is based on USNO-B1.0 stars referenced in (Mazaeva et al., GCN 18175). The continued shallow decay mentioned in Schulze et al. (GCN 18179) indeed can be explained by underlying host galaxy (Sanchez-Ramirez et al., GCN 18177).