TITLE: GCN CIRCULAR NUMBER: 25450 SUBJECT: GRB 190821A: Swift/UVOT Upper Limits DATE: 19/08/22 17:58:31 GMT FROM: Kira Simpson at PSU GRB 190821A: Swift/UVOT Upper Limits K. K. Simpson (PSU) and A. D'Ai (INAF-IASFPA) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 190821A 89 s after the BAT trigger (D'Ai et al., GCN Circ. 25427). No optical afterglow consistent with the XRT position (Goad et al. GCN Circ. 25436) 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 white_FC 89 239 147 >19.1 white 89 5595 344 >19.5 v 5806 6006 197 >18.3 b 5191 5390 197 >19.9 u 303 11409 336 >19.6 w1 9373 9551 175 >18.9 m2 6011 6164 151 >19.7 w2 5602 5801 197 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.53 in the direction of the burst (Schlegel et al. 1998).