TITLE: GCN CIRCULAR NUMBER: 13864 SUBJECT: GRB 121011A: Swift/UVOT Detection DATE: 12/10/12 19:58:04 GMT FROM: Stephen Holland at STScI S. T. Holland (STScI) and J. L. Racusin (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 121011A 109 s after the BAT trigger (Racusin et al., GCN Circ. 13845). A source consistent with the XRT position (Evans et al. GCN Circ. 13850) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 17:20:51.23 = 260.21346 (deg.) Dec (J2000) = +41:06:37.1 = +41.11030 (deg.) with an estimated uncertainty of 0.52 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 early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 109 258 147 18.96 +/- 0.06 v 4093 5729 393 19.81 +/- 0.21 b 3476 3676 197 19.51 +/- 0.18 u 4708 4908 197 19.67 +/- 0.18 w1 4503 15916 1183 >20.9 m2 4298 5933 393 >22.6 w2 3888 5524 393 >21.0 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.03 in the direction of the burst (Schlegel et al. 1998).