TITLE: GCN CIRCULAR NUMBER: 15375 SUBJECT: GRB 131024A: Swift/UVOT Upper Limits DATE: 13/10/25 03:21:43 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) 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 131024A 137 s after the BAT trigger (Racusin et al., GCN Circ. 15365). No optical afterglow consistent with the enhanced XRT position (Osborne et al., GCN Circ. 15367) 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) 136 286 147 >20.63 white 136 1542 392 >21.69 v 624 1592 116 >18.91 b 550 1517 97 >19.75 u (fc) 294 544 245 >19.99 u 294 1492 569 >20.49 uvw1 673 1468 97 >19.15 uvm2 648 1606 106 >18.99 uvw2 600 1567 116 >19.48 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.05 in the direction of the burst (Schlegel et al. 1998).