TITLE: GCN CIRCULAR NUMBER: 27276 SUBJECT: GRB 200228B: Mondy, TSHAO, AbAO and CrAO optical observations, afterglow candidate DATE: 20/03/01 15:21:19 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Pozanenko (IKI), S. Belkin (IKI), E. Klunko (ISTP), A. Kusakin (FAPHI), I. Reva (FAPHI), V. Rumyantsev (CrAO), R. Ya. Inasaridze (AbAO), E. Mazaeva (IKI), A. Volnova (IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 200228B (Laha et al., GCN 27254; Fermi GBM Team, GCN 27253) with AZT-33IK 1.5-m telescope of Sayan observatory (Mondy) starting on Feb. 28 (UT) 19:24:43. We detected an optical object near the enhanced XRT position of the XRT afterglow (Evans et al., GCN 27256). The object is absent in the Pan-STARRS DR1 catalog. The coordinates of the object are (J2000) 16:48:10.88 +16:59:04.5 with uncertainty of 0.5 arcsec in both coordinates. Next we observed the filed with Zeiss-1000 1-m telescope of Tien Shan Astronomical Observatory starting on Feb. 28 (UT) 23:08:56, Abastumani starting on Feb. 29 (UT) 01:38:45, Tien Shan Astronomical Observatory starting on Feb. 29 (UT) 23:08:56, and CrAO starting on Mar. 01 (UT) 00:58:28. Preliminary photometry of the object and the field is following. Date UT start t-T0 Filter Exp. OT Err UL(3sigma) telescope (mid, days) (s) 2020-02-28 19:24:43 0.351 R 15*120 21.8 0.3 21.7 AZT-33IK 2020-02-28 23:08:56 0.516 R 3480 n/d n/d 22.3 Z-1000 2020-02-29 01:38:45 0.616 R 46*60 n/d n/d 21.8 AS-32 2020-02-29 22:22:37 n/a R 5040 n/a n/a n/a Z-1000 2020-03-01 00:58:28 1.594 R 31*120 22.05 0.09 23.8 ZTSh Photometry is based on the USNO-B2.0 nearby stars. USNO-B1.0 R2 1069-0297786 18.42 1069-0297719 18.25 1069-0297797 14.78 The finding chart is available at http://193.232.11.154/GRB200228B/GRB200228B_AZT33IK_Z1000_ZTSh_FC.png (or http://grb.iki.rssi.ru/GRB200228B/GRB200228B_AZT33IK_Z1000_ZTSh_FC.png ). We suggest this object is a candidate in the afterglow of GRB 200228B after at least two epoch detections (see above), possible variability and absence of the bright object (R ~ 22) in the Pan-STARRS DR1. We did not detect any object at the position of NIR- candidate (Perley and Cockeram, GCN 27271).