TITLE: GCN CIRCULAR NUMBER: 30785 SUBJECT: GRB 210905A: Swift/UVOT Upper Limits DATE: 21/09/09 04:59:53 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18@psu.edu> M. H. Siegel (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 210905A 157 s after the BAT trigger (Sonbas et al., GCN Circ. 30765). No optical afterglow consistent with the XRT position (Beardmore et al. GCN Circ. 30768) 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 u_FC 157 407 246 >20.1 v 4193 4393 197 >19.3 b 3782 3982 197 >21.4 w1 4603 4803 197 >20.1 m2 4398 4597 197 >19.5 w2 3988 4188 197 >19.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.034 in the direction of the burst (Schlegel et al. 1998).