TITLE: GCN CIRCULAR NUMBER: 11139 SUBJECT: GRB 100823A: Swift/UVOT Upper Limits DATE: 10/08/24 04:37:39 GMT FROM: Margaret Chester at PSU M.M. Chester (PSU) and V. Mangano (INAF-IASFPA) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 100823A 78 s after the BAT trigger (Mangano et al., GCN Circ. 11135). No optical afterglow consistent with the enhanced Swift/XRT position (Goad et al., GCN Circ. 11136) 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 white and u finding chart (FC) and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 78 227 147 >20.1 u_FC 290 539 246 >19.4 white 78 17439 2181 >21.9 v 619 22361 1331 >20.5 b 545 16528 1278 >21.3 u 290 6512 639 >20.4 w1 669 6307 432 >20.2 m2 816 6102 413 >20.8 w2 767 18242 2082 >21.2 The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998).