TITLE: GCN CIRCULAR NUMBER: 12796 SUBJECT: GRB 120102A: Swift/UVOT Detection DATE: 12/01/02 12:41:27 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 120102A 121 s after the BAT trigger (Marshall et al., GCN Circ. 12794). A fading source consistent with the XRT position (Beardmore et al., GCN Circ. 12795) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 18:24:53.89 = 276.22456 (deg.) Dec (J2000) = +24:42:47.1 = 24.71309 (deg.) with an estimated uncertainty of 0.51 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the finding chart (FC) and early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white (FC) 121 271 147 18.10 ± 0.06 white 788 1014 167 19.9 ± 0.2 v 663 1239 78 18.16 ± 0.31 b 589 11310 1147 >20.8 u 334 583 246 18.52 ± 0.14 w1 713 6983 452 >20.2 m2 688 6778 452 >20.1 w2 639 12879 1112 >20.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.13 in the direction of the burst (Schlegel et al. 1998).