TITLE: GCN CIRCULAR NUMBER: 23663 SUBJECT: GRB 190109A: Swift/UVOT Upper Limits DATE: 19/01/09 20:36:24 GMT FROM: Kira Simpson at PSU GRB 190109A: Swift/UVOT Upper Limits K. K. Simpson (PSU) and J. D. Gropp (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 190109A 181 s after the BAT trigger (Gropp et al., GCN Circ. 23642). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 23644) 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 181 331 147 >99.0 u_FC 340 590 246 >17.3 white 181 12997 1291 >99.0 v 670 6867 490 >16.8 b 596 18739 1727 >18.6 u 340 24226 2551 >17.5 w1 720 23954 2223 >17.4 m2 695 23048 1357 >18.1 w2 646 6662 491 >17.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.05 in the direction of the burst (Schlegel et al. 1998).