TITLE: GCN CIRCULAR NUMBER: 26611 SUBJECT: GRB 191228A: Swift/UVOT Upper Limits DATE: 19/12/29 21:38:22 GMT FROM: Sam LaPorte at PSU GRB 191228A: Swift/UVOT Upper Limits J. D. Gropp (PSU) and M. G. Bernardini (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 191228A 131 s after the BAT trigger (Bernardini et al., GCN Circ. 26601). No optical afterglow consistent with the XRT position (Bernardini et al. GCN Circ. 26601) 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 first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 131 281 147 >20.3 u_FC 289 539 246 >19.6 white 131 1009 327 >20.6 v 619 811 39 >18.2 b 545 737 39 >19.2 u 289 712 265 >19.6 w1 668 860 39 >18.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998).