TITLE: GCN CIRCULAR NUMBER: 20644 SUBJECT: GRB 170208A: Swift/UVOT Upper Limits DATE: 17/02/09 14:45:54 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) and A. Cholden-Brown (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 170208A 125 s after the BAT trigger (Cholden-Brown et al., GCN Circ. 20631). No optical afterglow consistent with the enhanced XRT position (Evans et al. GCN Circ. 20634) 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 125 275 148 >21.4 u_FC 337 587 246 >20.7 white 125 1365 373 >21.9 v 667 1415 97 >19.3 b 593 1503 87 >19.4 u 337 1489 324 >20.2 w1 717 1464 78 >19.4 w2 642 1390 97 >19.3 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.13 in the direction of the burst (Schlegel et al. 1998).