TITLE: GCN CIRCULAR NUMBER: 18218 SUBJECT: GRB 150831A: Swift/UVOT Upper Limits DATE: 15/09/01 00:14:09 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) and A. Y. Lien (GSFC/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150831A 88 s after the BAT trigger (Lien et al., GCN Circ. 18209). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 18212) 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 88 238 147 >20.5 u_FC 300 550 246 >19.9 white 88 6622 746 >21.2 v 631 17885 1356 >19.8 b 557 6417 452 >20.4 u 300 12784 1326 >21.0 w1 680 12112 1153 >21.3 m2 655 18529 1750 >21.3 w2 607 16972 1357 >21.1 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.11 in the direction of the burst (Schlegel et al. 1998).