TITLE: GCN CIRCULAR NUMBER: 18381 SUBJECT: GRB 151001A: Swift/UVOT Detection DATE: 15/10/02 12:44:45 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (UCL-MSSL) 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 151001A 46 s after the BAT trigger (Stamatikos et al., GCN Circ. 18373). A fading source consistent with the enhanced XRT position (Beardmore et al. GCN Circ. 18376) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 15:34:54.90 = 233.72875 (deg.) Dec (J2000) = +10:58:02.2 = 10.96728 (deg.) with an estimated uncertainty of 0.43 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 67 217 147 17.82 ± 0.06 white 559 578 20 19.5 ± 0.3 v 46 1403 110 18.78 ± 0.29 b 534 1502 97 19.60 ± 0.29 u 279 529 246 19.13 ± 0.15 w1 657 1453 97 >19.3 m2 806 1428 39 >18.0 w2 1358 1552 39 >18.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998).