TITLE: GCN CIRCULAR NUMBER: 17639 SUBJECT: GRB 150323C: Mondy optical observations DATE: 15/03/25 13:29:01 GMT FROM: Alexei Pozanenko at IKI, Moscow E. Mazaeva (IKI), A. Volnova (IKI), E. Klunko (ISTP), I. Korobtsev (ISTP), M. Eselevich (ISTP), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the GRB 150323C (Amaral-Rogers et al., GCN 17621) with AZT-33IK telescope of Sayan observatory (Mondy) starting on Mar., 23 (UT) 11:42:02. We obtained several images in R-filter of 120 s exposure. Within enhanced Swift-XRT error circle (Osborne et al., GCN 17633) we clearly detect optical afterglow (Xu et al. GCN 17625, Xin et al. GCN 17631; Watson et al. GCN 17632) in a combined image. Preliminary photometry of the afterglow is following Date UT start t-T0 Filter Exp. OT Err. (mid, days) (s) 2015-03-24 15:14:09 0.95405 R 44*120 22.4 0.3 Photometry is based on SDSS DR9 stars: SDSS9_id R(Lupton) J125023.08+501048.2 16.84 J125032.04+501021.5 18.37 J125016.28+501035.8 18.22