TITLE: GCN CIRCULAR NUMBER: 16187 SUBJECT: GRB 140428A: Swift/UVOT Upper Limits DATE: 14/04/29 21:13:07 GMT FROM: Frank Marshall at GSFC F. E. Marshall (NASA/GSFC) and D. Kocevski (NASA/GSFC/ORAU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 140428A 104 s after the BAT trigger (Kocevski et al., GCN Circ. 16177). No optical afterglow consistent with the optical position (Perley, GCN_Circ. 16180) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 104 254 147 >21.2 v 5454 5653 197 >20.3 b 4838 5039 197 >21.4 u 264 271 7 >19.5 uw1 5864 6030 197 >20.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.009 in the direction of the burst (Schlegel et al. 1998).