TITLE: GCN CIRCULAR NUMBER: 15195 SUBJECT: GRB 130907A: Swift/UVOT Detection DATE: 13/09/08 17:37:39 GMT FROM: Samantha Oates at MSSL S. R. Oates (UCL-MSSL) and M. J. Page (UCL-MSSL) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 130907A 74 s after the BAT trigger (Page et al., GCN Circ. 15183). A source consistent with the XRT position (Page et al. GCN Circ. 15183) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 14:23:34.04 = 215.89183 (deg.) Dec (J2000) = +45:36:27.1 = 45.60753 (deg.) with an estimated uncertainty of 0.50 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 74 224 147 15.45 +/- 0.02 v 616 636 20 16.29 +/- 0.16 b 542 562 20 16.78 +/- 0.12 u 286 536 246 15.87 +/- 0.04 w1 666 1113 117 18.54 +/- 0.31 m2 641 1606 117 >19.2 w2 592 786 38 >18.7 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.01 in the direction of the burst (Schlegel et al. 1998).