TITLE: GCN CIRCULAR NUMBER: 18111 SUBJECT: GRB 150801B: Swift/UVOT Upper Limits DATE: 15/08/02 22:58:24 GMT FROM: Lea Hagen at PSU L. M. Z. Hagen (PSU) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150801B 84 s after the BAT trigger (Sbarufatti et al., GCN Circ. 18104). No optical afterglow consistent with the XRT position (Evans et al., GCN Circ. 18108) 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 83 233 147 >20.17 white 575 12513 1345 >21.35 v 625 16812 901 >19.63 b 551 11601 1264 >20.68 u_FC 295 545 245 >19.42 u 699 7399 490 >19.53 uvw1 1105 7194 432 >19.41 uvw2 4943 13218 884 >19.89 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.24 in the direction of the burst (Schlegel et al. 1998).