TITLE: GCN CIRCULAR NUMBER: 11038 SUBJECT: GRB 100802A: Swift/UVOT Possible Optical Afterglow DATE: 10/08/02 15:59:42 GMT FROM: Alice Breeveld at MSSL-UCL A. Breeveld (MSSL/UCL) and E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 100802A 89 s after the BAT trigger (Troja et al., GCN Circ. 11031). Using the data from the most recent telemetry, there is a tentative detection of an optical afterglow at the position given by Siegel et al., GCN Circ. 11032, in the early white and u exposures. Preliminary detections and later 3-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC) exposures and subsequent summed exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 89 238 147 20.7 ± 0.24 u_FC 301 551 246 19.57 ± 0.22 white 581 5566 327 21.85 ± 0.48 (2.4 sigma sig) v 632 5977 432 >20.6 b 557 6754 388 >21.2 u 706 6593 412 >20.92 w1 682 6388 432 >20.9 m2 657 6183 432 >20.6 w2 608 5772 432 >21.0 The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.12 in the direction of the burst (Schlegel et al. 1998).