TITLE: GCN CIRCULAR NUMBER: 10901 SUBJECT: GRB 100628A: Swift/UVOT Upper Limits DATE: 10/06/28 22:48:13 GMT FROM: Stefan Immler at NASA/GSFC S. Immler (CRESST/GSFC/UMD) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 100628A 90 s after the BAT trigger (Immler et al., GCN Circ. 10895). No optical afterglow consistent with the XRT position (Starling et al., GCN Circ. 10899) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 90 239 147 >20.2 u_FC 302 551 246 >19.4 white 90 11409 1498 >21.4 v 631 12968 1099 >19.5 b 557 7133 471 >20.1 u 302 6928 697 >20.2 w1 680 6722 471 >19.6 m2 4882 6517 393 >19.3 w2 607 12315 1176 >20.3 The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.17 in the direction of the burst (Schlegel et al. 1998).