TITLE: GCN CIRCULAR NUMBER: 13047 SUBJECT: GRB 120311B: Swift/UVOT Upper Limits DATE: 12/03/12 12:15:09 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (MSSL-UCL) and F. E. Marshall (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 120311B 3072 s after the BAT trigger (Marshall et al., GCN Circ. 13038). No optical afterglow consistent with the XRT position (Osborne et al., GCN Circ. 13042) 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 3072 3222 147 >21.4 white 3072 16503 2114 >22.8 v 3228 21300 2013 >20.3 b 4048 15591 1233 >20.7 u 3843 5479 393 >19.7 w1 3638 22969 1136 >20.9 m2 3433 22206 1082 >20.8 w2 4460 17192 1754 >21.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.52 in the direction of the burst (Schlegel et al. 1998).