TITLE: GCN CIRCULAR NUMBER: 14424 SUBJECT: GRB 130420A: Swift/UVOT Detection DATE: 13/04/20 21:06:26 GMT FROM: Samantha Oates at MSSL S. R. Oates, M. De Pasquale, 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 130420A 739 s after the BAT trigger (Page et al., GCN Circ. 14406). A source consistent with the XRT position (Goad et al. GCN Circ. 14416) is detected in the initial UVOT exposures. The GRB is detected in all filters and is therefore consistent with being at a redshift of ~<1.6. The preliminary UVOT position is: RA (J2000) = 13:04:25.55 = 196.10647 (deg.) Dec (J2000) = +59:25:27.1 = 59.42420 (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 739 888 147 17.14 +/- 0.03 v 1072 1092 20 17.66 +/- 0.31 b 1171 1191 19 18.13 +/- 0.21 u 1146 1166 20 17.19 +/- 0.17 w1 1122 1141 19 17.51 +/- 0.29 m2 1097 1465 58 18.30 +/- 0.31 w2 1049 1240 39 18.50 +/- 0.33 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).