TITLE: GCN CIRCULAR NUMBER: 21001 SUBJECT: GRB 170317A: SAO RAS optical observations DATE: 17/04/07 20:23:42 GMT FROM: Moskvitin Alexander at SAO RAS A. Moskvitin (SAO RAS), E. Mazaeva (IKI), A. Pozanenko (IKI), A. Volnova (IKI), on behalf of larger GRB follow-up collaboration: We observed the field of GRB 170317A (LaPorte et al. GCN 20885) with the SAO RAS telescope Zeiss-1000 + CCD photometer on March, 17 (18:12:00--19:58:03 UT). We obtained several images in Rc band. The optical afterglow (LaPorte et al., GCN 20885; Mazaeva et al., GCN 20886; Xin et al., GCN 20888; Mao et al., GCN 20889; Kuroda et al., GCN 20899) is detected in a stacked frame. Preliminary photometry is following Date UT start t-T0 Filter Exp. OT Err. UL (mid, days) (s) 2017-03-17 18:12:00 0.38823 Rc 15*300 22.3 0.3 22.6 Photometry is based on nearby USNO-B1.0 stars previously used in GCN 20886.