TITLE: GCN CIRCULAR NUMBER: 13057 SUBJECT: GRB 120312A: Swift/UVOT Upper Limits DATE: 12/03/13 11:11:56 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) and M. Stamatikos (OSU/NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 120312A 105 s after the BAT trigger (Stamatikos et al., GCN Circ. 13049). No optical afterglow consistent with the XRT position (Mangano et al., GCN Circ 13053) or the WHT optical candidate position (Tanvir et al., GCN Circ 13055) 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 105 255 147 >21.3 u_FC 318 567 246 >20.6 white 105 7764 861 >21.9 v 647 18848 1378 >20.5 b 573 7559 568 >20.9 u 318 13854 1583 >21.3 w1 696 13039 1434 >21.0 m2 844 19630 1998 >21.4 w2 795 17934 1434 >21.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.071 in the direction of the burst (Schlegel et al. 1998).