TITLE: GCN CIRCULAR NUMBER: 23437 SUBJECT: GRB 181123B: Swift/UVOT Upper Limits DATE: 18/11/23 15:38:28 GMT FROM: Samantha Oates at MSSL GRB 181123B: Swift/UVOT Upper Limits S. R. Oates (U.Warwick) and A. Y. Lien (GSFC/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 181123B 84 s after the BAT trigger (Lien et al., GCN Circ. 23432). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 23434) 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 84 233 147 >20.3 u_FC 296 546 246 >19.5 white 84 6529 727 >21.0 v 626 10922 1228 >19.8 b 551 6324 432 >20.1 u 296 6119 659 >20.1 w1 4278 12566 1113 >20.2 m2 5509 11827 1082 >20.5 w2 5100 6734 393 >19.8 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.03 in the direction of the burst (Schlegel et al. 1998).