TITLE: GCN CIRCULAR NUMBER: 21984 SUBJECT: GRB 171007A: Swift/UVOT Upper Limits DATE: 17/10/10 16:42:31 GMT FROM: Frank Marshall at GSFC F. E. Marshall (NASA/GSFC) and J. K. Cannizzo (NASA/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 171007A 77 s after the BAT trigger (Cannizzo et al., GCN Circ. 21976). No optical afterglow consistent with the enhanced XRT position (Beardmore et al. GCN Circ. 21979) 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 77 227 147 >20.7 u_FC 291 540 246 >20.4 white 77 6966 805 >21.7 v 620 7377 529 >19.5 b 546 6761 510 >20.8 u 291 6556 559 >20.7 w1 669 6351 333 >20.3 m2 644 7572 480 >19.9 w2 596 7172 529 >20.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998).