TITLE: GCN CIRCULAR NUMBER: 18931 SUBJECT: GRB 160123A: Swift/UVOT Upper Limits DATE: 16/01/23 21:44:10 GMT FROM: Massimiliano de Pasquale at IASF-Palermo M. De Pasquale (UCL-MSSL) and D. Malesani (DARK/NBI) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 160123A 82 s after the BAT trigger (Malesani et al., GCN Circ. 18926). No optical afterglow consistent with the XRT position (Beardmore et al. GCN Circ. 18927) 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 82 231 147 >20.7 u_FC 296 545 246 >19.9 white 82 1196 1041 >21.8 v 626 11136 1191 >20.3 b 551 17792 1337 >21.4 u 296 17792 1563 >20.4 w1 675 12760 1152 >19.2 m2 650 12040 1160 >20.0 w2 601 6977 471 >21.0 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.10 in the direction of the burst (Schlegel et al. 1998).