TITLE: GCN CIRCULAR NUMBER: 23064 SUBJECT: GRB 180728A: Swift/UVOT Detection DATE: 18/07/31 03:04:49 GMT FROM: Sam LaPorte at PSU GRB 180728A: Swift/UVOT Detection S. J. LaPorte (PSU) and R. L. C. Starling (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180728A 1740 s after the BAT trigger (Starling et al., GCN Circ. 23046). A source consistent with the enhanced XRT position (Osborne et al. GCN Circ. 23051) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 16:54:15.53 = 253.56472 (deg.) Dec (J2000) = -54:02:40.2 = -54.04451 (deg.) with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence), consistent with MASTER OT J165415.75-540239.27 (Lipunov et al., GCN #23050). Preliminary detections 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 1740 1890 147 16.25 +/- 0.03 white 7713 15148 465 17.28 +/- 0.03 v 1897 1917 20 16.07 +/- 0.14 b 1995 2013 18 16.58 +/- 0.10 u 1970 1990 20 15.93 +/- 0.10 w1 1946 1966 20 16.20 +/- 0.17 m2 1921 2114 39 16.60 +/- 0.18 w2 2045 2065 19 16.37 +/- 0.19 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.29 in the direction of the burst (Schlegel et al. 1998).