TITLE: GCN CIRCULAR NUMBER: 18227 SUBJECT: GRB 150831B: Swift/UVOT Upper Limits DATE: 15/09/01 20:59:18 GMT FROM: Frank Marshall at GSFC F. E. Marshall (NASA/GSFC) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150831B 3089 s after the BAT trigger (Marshall et al., GCN Circ. 18215). No optical afterglow consistent with the refined XRT position (D'Avanzo et al., GCN Circ. 18222) is detected in the initial UVOT exposures. We note that this is a very crowded field. 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 3089 3239 147 >20.6 v 3246 3445 197 >18.2 b 8838 9745 885 >20.3 u 3861 5659 158 >19.4 w1 3656 3856 197 >19.2 m2 3451 3651 197 >20.2 The magnitudes in the table are not corrected for the large Galactic extinction in the direction of the burst (Schlegel et al. 1998).