TITLE: GCN CIRCULAR NUMBER: 18057 SUBJECT: GRB 150724A: Swift/UVOT Upper Limits DATE: 15/07/24 14:41:21 GMT FROM: Massimiliano de Pasquale at IASF-Palermo M. De Pasquale (UCL-MSSL) and J. L. Racusin (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150724A 108 s after the BAT trigger (Racusin et al., GCN Circ. 18050). No optical afterglow consistent with the XRT position (Goad et al. GCN Circ. 18054) 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 summed exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u_FC 108 358 246 >19.7 v 415 6930 510 >19.2 b 364 12898 1165 >20.6 u 108 12238 1769 >20.7 w1 464 11324 1387 >20.5 m2 439 7135 502 >19.9 w2 390 6726 529 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.27 in the direction of the burst (Schlegel et al. 1998). -- Dr. Massimiliano De Pasquale Research associate - Swift UVOT scientist Mullard Space Science Laboratory, University College London