TITLE: GCN CIRCULAR NUMBER: 21141 SUBJECT: GRB 170524A: Swift/UVOT Upper Limits DATE: 17/05/25 12:37:02 GMT FROM: Sam Emery at MSSL-UCL S.W.K. Emery (UCL-MSSL) and J.G. Gropp (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 170524A 67 s after the BAT trigger (Gropp et al., GCN Circ. 21135). No optical afterglow consistent with the XRT position (Evans et al. GCN Circ. 21136) 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 67 217 147 >20.4 u_FC 280 529 246 >19.5 white 67 1007 334 >20.6 v 610 1058 58 >17.9 b 535 1157 58 >18.7 u 280 1132 285 >19.5 w1 660 1107 58 >18.3 m2 1063 1082 19 >17.3 w2 586 1033 58 >18.6 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 2.82 in the direction of the burst (Schlegel et al. 1998).