TITLE: GCN CIRCULAR NUMBER: 23283 SUBJECT: GRB 180930A: Swift/UVOT Upper Limits DATE: 18/09/30 20:40:45 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (UCL-MSSL) and A. Tohuvavohu (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180930A 212 s after the BAT trigger (Tohuvavohu et al., GCN Circ. 23279). No optical afterglow consistent with the XRT position (Evans GCN Circ. 23280) 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 212 362 147 >21.2 white 212 2818 602 >21.1 v 517 2620 226 >20.1 b 443 2718 240 >20.7 u 418 2693 245 >19.7 w1 394 2669 253 >20.8 m2 369 2644 233 >19.3 w2 659 2595 194 >19.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998).