TITLE: GCN CIRCULAR NUMBER: 13962 SUBJECT: GRB 121108A: Swift/UVOT Upper Limits DATE: 12/11/09 18:03:29 GMT FROM: Frank Marshall at GSFC F. E. Marshall (NASA/GSFC) and T. N. Ukwatta (MSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 121108A 64 s after the BAT trigger (Ukwatta et al., GCN Circ. 13952). No optical afterglow consistent with the XRT position (Beardmore et al. GCN Circ. 13959) 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 64 213 147 >20.9 u_FC 276 526 246 >20.5 white 64 1721 412 >21.3 v 605 1771 136 >19.6 b 531 1697 117 >19.9 u 276 1672 362 >20.6 w1 655 1814 129 >19.6 m2 1429 1623 39 >19.6 w2 581 1747 136 >19.8 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.37 in the direction of the burst (Schlegel et al. 1998).