TITLE: GCN CIRCULAR NUMBER: 18393 SUBJECT: Trigger 657564 / GRB 151004A: Swift/UVOT Upper Limits DATE: 15/10/05 12:13:24 GMT FROM: Massimiliano de Pasquale at IASF-Palermo M. De Pasquale (UCL-MSSL) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of the trigger 657564 (possible GRB 151004A) 3613 s after the BAT trigger (Cenko et al., GCN Circ. 18389). No optical afterglow consistent with the BAT position 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 3613 3763 147 >20 white 3613 4994 344 >20.3 v 3770 5404 393 >18.7 b 4590 4789 197 >19.2 u 4384 4584 197 >18.9 w1 4179 4379 197 >19.0 m2 3974 5565 350 >19.3 w2 5000 5200 197 >19.1 The magnitudes in the table are not corrected for the heavy Galactic extinction due to the reddening of E(B-V) = 1.03 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