GCN Circular 20574
A. A. Breeveld (UCL-MSSL), M. Stamatikos (OSU) and F. E. Marshall (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 170131A 78368 s after the BAT trigger (Palmer, GCN Circ. 20570) using the UVW2 filter only. No optical afterglow consistent with the XRT source 1 position (Melandri et al., GCN Circ. 20573) is detected in the initial UVOT exposures. However, there is a USNO-B1.0 source at this position (USNO-B1.0 1540-029147), but it is not detected in the UVW2 filter. The preliminary 3-sigma upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures is: Filter T_start(s) T_stop(s) Exp(s) Mag w2 78368 96539 4888 >21.2 The magnitude in the table is not corrected for the large, but uncertain Galactic extinction due to the reddening of E(B-V) = 1.19 in the direction of the burst (Schlegel et al. 1998).