TITLE: GCN CIRCULAR NUMBER: 10688 SUBJECT: GRB 100424A: Swift/UVOT Upper Limits DATE: 10/04/25 14:39:39 GMT FROM: Peter Curran at MSSL P.A. Curran (MSSL-UCL) and E. Hoversten (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 100424A 128 s after the BAT trigger (Hoversten et al., GCN Circ. 10667). No optical afterglow consistent with the refined XRT position (Evans et al., GCN Circ. 10669) or the proposed NIR counterpart (Cenko et al. (GCN Circ. 10682) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the initial finding charts (FC) and exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag ---------------------------------------------- white 128 278 147 >20.8 (FC) u 288 537 246 >20.0 (FC) white 128 2046 444 >21.2 v 618 1930 156 >19.2 b 543 2028 156 >20.1 u 288 2003 382 >20.1 w1 668 1979 156 >19.7 m2 642 1955 97 >19.1 w2 594 5584 193 >20.0 The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.08 in the direction of the burst (Schlegel et al. 1998).