TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5519 SUBJECT: GRB060904b: Optical observations with Swift/UVOT DATE: 06/09/04 14:50:10 GMT FROM: Samantha Oates at MSSL S. R. Oates (UCL-MSSL), D. Grupe (PSU) on behalf of the Swift UVOT team The Swift Ultra-Violet/Optical Telescope (UVOT) began observations of GRB060904b at 02:32:14 UT, ~71 seconds after the initial Swift BAT trigger (Grupe et al, GCN 5505). An optical counterpart was detected with the V filter at a position RA(J2000)= (03h,52m,50.54s, -00o43'31.1'') to within 0.5''. An optical afterglow was detected in V, B, U, UVW1, UVM2 and UVW2 filters. The photometery results are given for the 6 filters below: Filter Tstart Tstop Magnitudes and UL --------------------------------------------- V 71 316 18.64 +/- 0.33 4732 4931 19.16 +/- 0.36 5960 6100 18.25 3 sigma UL B 4322 4521 18.98 +/- 0.15 5550 5749 19.56 +/- 0.28 U 4117 4316 18.32 +/- 0.19 5346 5545 18.65 +/- 0.23 UVW1 3913 4112 18.78 +/- 0.31 5141 5340 19.11 +/- 0.36 UVM2 3708 3907 18.88 +/- 0.36 4936 5135 19.66 +/- 0.55 UVW2 4528 4727 18.96 +/- 0.33 5756 5955 19.32 +/- 0.41 --------------------------------------------- The values quoted above are not corrected for the expected Galactic extinction of E_{B-V}=0.173.