TITLE: GCN CIRCULAR NUMBER: 22531 SUBJECT: GRB 180324A: Swift/UVOT Upper Limits DATE: 18/03/24 23:27:32 GMT FROM: Sam LaPorte at PSU GRB 180324A: Swift/UVOT Upper Limits S. J. Laporte (PSU) and E. Sonbas (Adiyaman Univ.) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180324A 72 s after the BAT trigger (Sonbas et al., GCN Circ. 22524). No optical afterglow consistent with the XRT position (Goad et al. GCN Circ. 22529) or RATIR position (Butler et al. GCN Circ. 22528) 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 72 221 147 >19.8 u_FC 284 534 246 >19.3 white 72 12383 1552 >21.3 v 614 13894 1172 >19.5 b 539 8158 549 >20.9 u 284 7992 814 >20.3 w1 664 7787 471 >20.2 w2 6970 13290 1082 >21.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.90 in the direction of the burst (Schlegel et al. 1998).