TITLE: GCN CIRCULAR NUMBER: 14425 SUBJECT: GRB 130420B: Swift/UVOT Upper Limits DATE: 13/04/20 21:28:15 GMT FROM: Massimiliano de Pasquale at MSSL-UCL M. De Pasquale, S. R. Oates (MSSL-UCL) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 130420B 57 s after the BAT trigger (Oates et al., GCN Circ. 14411). No optical afterglow consistent with the XRT position (Page et al., GCN circ. 14421) is detected in the initial and summed UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: Filter T_start(s) T_stop(s) Exp(s) Mag white 57 5841 460 >21.7 v 4707 4907 197 >19.6 b 4091 5727 393 >20.9 u 3886 5521 393 >20.6 w1 5117 5317 197 >20.1 m2 4912 5111 197 >19.8 w2 4502 4702 197 >20.1 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998).