TITLE: GCN CIRCULAR NUMBER: 27439 SUBJECT: GRB 200324A: Swift/UVOT Upper Limits DATE: 20/03/25 12:48:41 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (UCL-MSSL) and S. Dichiara (NASA/GSFC/UMCP) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 200324A 215 s after the BAT trigger (Dichiara et al., GCN Circ. 27428). No optical afterglow consistent with the XRT position (Beardmore et al. GCN Circ. 27430) 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 215 365 147 >21.0 u_FC 374 624 246 >20.6 white 215 1376 373 >21.7 v 704 1427 78 >18.9 b 630 1527 97 >19.8 u 374 1327 304 >20.2 w1 754 1477 78 >19.1 w2 1381 1401 19 >19.1 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.01 in the direction of the burst (Schlegel et al. 1998).