TITLE: GCN CIRCULAR NUMBER: 17559 SUBJECT: GRB 150309A: Swift/UVOT Upper Limits DATE: 15/03/10 13:16:03 GMT FROM: Samantha Oates at MSSL S. R. Oates (IAA-CSIC/UCL-MSSL) and J. R. Cummings (NASA/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150309A 140 s after the BAT trigger (Cummings et al., GCN Circ. 17553). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 17555) 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 140 290 147 >20.3 u_FC 299 549 246 >19.4 white 140 12463 881 >21.1 v 630 6293 432 >19.3 b 555 12046 1121 >20.8 u 299 17720 2241 >21.1 w1 679 16806 1318 >20.8 m2 654 6498 432 >20.1 w2 605 6089 432 >20.3 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.14 in the direction of the burst (Schlegel et al. 1998).