TITLE: GCN CIRCULAR NUMBER: 31759 SUBJECT: GRB 220306B: Swift/UVOT Upper Limits DATE: 22/03/15 13:10:24 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) and Caputo (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 220306B 89 s after the BAT trigger (Caputo et al., GCN Circ. 31697). No optical afterglow consistent with the XRT position (Evans et al. GCN Circ. 31700) 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 89 239 147 >19.9 u_FC 302 552 246 >20.1 white 89 1716 402 >20.4 v 631 1601 117 >18.7 b 557 1701 117 >19.9 u 302 1676 343 >20.2 w1 680 1650 117 >19.3 m2 656 1626 117 >19.4 w2 607 5204 213 >19.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.578 in the direction of the burst (Schlegel et al. 1998).