TITLE: GCN CIRCULAR NUMBER: 17909 SUBJECT: GRB 150607A: Swift/UVOT Detection DATE: 15/06/08 00:28:17 GMT FROM: Lea Hagen at PSU L. M. Z. Hagen (PSU) and V. D'Elia (ASDC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150607A 137 s after the BAT trigger (D'Elia et al., GCN Circ. 17904). A source consistent with the XRT position (Osborne et al. GCN Circ. 17905) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 09:19:57.20 = 139.98833 (deg.) Dec (J2000) = +68:26:10.3 = 68.43619 (deg.) with an estimated uncertainty of 0.44 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 137 286 146 18.10 +/- 0.07 white 628 1204 205 20.04 +/- 0.31 white 1358 7668 412 >20.55 v 118 128 9 16.71 +/- 0.35 v 678 7955 446 >19.02 b 604 7463 367 >19.65 u 348 598 245 18.88 +/- 0.27 u 753 7258 352 >19.37 uvw1 728 7053 352 >19.60 uvm2 1084 6848 313 >19.74 uvw2 654 7874 568 >20.30 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.07 in the direction of the burst (Schlegel et al. 1998).