TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4058 SUBJECT: GRB051001: Swift UVOT Upper Limits DATE: 05/10/02 18:56:50 GMT FROM: Caryl Gronwall at PSU/Swift-UVOT F. Marshall(GSFC), A. Moretti (OAB), J. Nousek (PSU), W. Voges (MPE), N. Gehrels (GSFC) report on behalf of the Swift/UVOT team. The Swift/UVOT instrument began observing the field of the burst GRB051001 at 11:14:45 UT, 189 seconds after the BAT trigger (Moretti et al., GCN 4051). Within the 6 arcsec radius XRT error circle (GCN 4051), no new optical/UV source is detected. We derive the following 3-sigma upper limit magnitudes on any optical/UV counterpart in the summed images in each UVOT filter (from 6" radius apertures centered on the XRT location, which is representative of the local background). Filter T_range(sec) Exp(sec) 3-sig UL V 189-289 100 18.9 V 189-11522 1189 20.1 B 335-6646 1077 21.2 U 321-5738 1106 21.0 UVW1 307-13221 952 20.9 UVW2 11530-12429 900 21.4 UVM2 6655-7435 780 21.5