TITLE: GCN CIRCULAR NUMBER: 23317 SUBJECT: GRB 181010A: Swift/UVOT Detection DATE: 18/10/10 12:55:25 GMT FROM: Sam Emery at MSSL-UCL S.W.K. Emery (UCL-MSSL) and A. Melandri (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 181010A 96 s after the BAT trigger (Melandri et al., GCN Circ. 23309). A source consistent with the XRT position (Evans et al. GCN Circ. 23313) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 03:30:16.89 = 52.57038 (deg.) Dec (J2000) = -23:02:15.4 = -23.03761 (deg.) with an estimated uncertainty of 0.49 arc sec. (radius, 90% confidence), consistent with (MASTER-OAFA, Gorbovskoy et al., GCN Circ. 23310; LCO Cerro Tololo, Martone et al., GCN Circ. 23311; RATIR, Troja et al., GCN Circ. 23312; VLT/X-shooter, Vielfaure et al., GCN Circ. 23315) Preliminary detections and 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 96 246 147 19.42 +/- 0.09 white 589 6359 247 >21.0 v 3867 5503 393 >19.4 b 564 6323 413 >20.9 u 309 6117 639 >20.6 uvw1 4277 5912 393 >20.1 uvm2 4072 5707 393 >20.7 uvw2 5098 5298 197 >20.5 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).