TITLE: GCN CIRCULAR NUMBER: 27268 SUBJECT: GRB 200228B: Swift/UVOT Upper Limits DATE: 20/02/28 22:23:32 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (UCL-MSSL) and S. L. Laha (GSFC/UMBC/CRESST) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 200228B 137 s after the BAT trigger (Laha et al., GCN Circ. 27254). No optical afterglow consistent with the XRT position (Evans et al., GCN Circ. #27256 is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u_FC 137 387 246 >20.1 v 4992 10685 676 >20.1 b 4580 6012 393 >20.6 u 137 5807 442 >20.4 w1 5402 5602 197 >19.5 m2 5197 5396 197 >19.8 w2 4786 6218 393 >19.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.092 in the direction of the burst (Schlegel et al. 1998).