TITLE: GCN CIRCULAR NUMBER: 30903 SUBJECT: GRB 210930A: Swift/UVOT Upper Limits DATE: 21/09/30 22:33:53 GMT FROM: Alexander Belles at PSU/Swift <aub1461@psu.edu> A. Belles (PSU) and V. D'Elia (SSDC & INAF-OAR) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 210930A 144 s after the BAT trigger (D'Elia et al., GCN Circ. 30897). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 30900) 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 144 293 147 >19.9 u_FC 302 551 246 >19.6 white 144 1722 411 >20.6 v 631 1773 136 >18.7 b 559 1873 134 >19.6 u 302 1848 363 >19.7 w1 681 1824 136 >19.5 m2 655 1450 39 >18.7 w2 607 1747 117 >20.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.010 in the direction of the burst (Schlegel et al. 1998).