TITLE: GCN CIRCULAR NUMBER: 15313 SUBJECT: GRB 131004A: Swift/UVOT Detection DATE: 13/10/05 16:42:18 GMT FROM: MSSL Swift/UVOT team at MSSL/Swift M. De Pasquale (UCL-MSSL) and L. M. Z. Hagen (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 131004A 75 s after the BAT trigger (Hagen et al., GCN Circ. 15303). A source consistent with the XRT position (Evans et al. GCN Circ. 15308) and the position of the source given in Xu et al. (GCN Circ. 15304) is detected in the initial and summed UVOT exposures. The preliminary coordinates of this source are: RA (J2000) = 19:44:27.09 = 296.11287 (deg.) Dec (J2000) = -02:57:30.4 = -2.95844 (deg.) with an estimated uncertainty of 0.55 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_FC 75 225 147 19.23 ± 0.11 white 75 5688 520 20.18 ± 0.12 u_FC 288 537 246 19.96 ± 0.34 u 288 6715 659 20.72 ± 0.40 v 617 6100 432 >20.24 b 543 6770 285 >21.0 w1 666 6510 432 >20.9 m2 814 6305 413 >20.8 w2 593 5895 432 >21.0 The magnitudes in the table are not corrected for substantial Galactic extinction due to the reddening of E(B-V) = 0.28 in the direction of the burst (Schlegel et al. 1998).