TITLE: GCN CIRCULAR NUMBER: 20552 SUBJECT: GRB 170127A: Swift/UVOT Upper Limits DATE: 17/01/27 22:44:14 GMT FROM: Frank Marshall at GSFC F. E. Marshall (NASA/GSFC) and C. B. Markwardt (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 170127A 102 s after the BAT trigger (Markwardt et al., GCN Circ. 20538). No optical afterglow consistent with the enhanced XRT position (Evans et al. GCN Circ. 20548) 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 u_FC 102 351 246 >20.5 v 409 1533 136 >18.7 b 359 1632 175 >20.4 u 102 1607 529 >20.7 w1 458 1583 136 >19.4 m2 434 1558 136 >20.0 w2 385 1658 175 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.07 in the direction of the burst (Schlegel et al. 1998).