TITLE: GCN CIRCULAR NUMBER: 23664 SUBJECT: GRB 190109B: Swift/UVOT Upper Limits DATE: 19/01/09 20:37:32 GMT FROM: Kira Simpson at PSU GRB 190109B: Swift/UVOT Upper Limits K. K. Simpson (PSU) and B. Sbarufatti (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 190109B 91 s after the BAT trigger (Sbarufatti et al., GCN Circ. 23648). No optical afterglow consistent with the XRT position (Beardmore et al. GCN Circ. 23652) 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 91 241 147 >20.7 u_FC 303 553 246 >20.7 white 91 6461 727 >22.1 v 634 6860 441 >20.4 b 559 6256 432 >20.9 u 303 6050 470 >21.0 w1 683 5845 236 >20.2 m2 5440 5640 197 >20.8 w2 5030 6666 393 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.72 in the direction of the burst (Schlegel et al. 1998).