TITLE: GCN CIRCULAR NUMBER: 8192 SUBJECT: GRB 080905B: Refined UVOT Analysis DATE: 08/09/07 00:43:31 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland (CRESST/USRA/GSFC) & M. C. Stroh (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT observed the field of GRB 080905B starting 94 s after the BAT trigger (Stroh et al., 2008, GCNC. 8182). Settled observations started at T + 113 s. We detect the optical afterglow (Stroh et al., GCNC 8182) in the v and white filters at the UVOT-enhanced location of the XRT afterglow (Osborne, et al., 2008, GCNC 8089). There is an uncertain detection in the b filter. The refined UVOT source position is RA (J2000.0) = 20:06:57.89 Dec (J2000.0) = -62:33:47.0 with an estimated uncertainty of 0.7 arcsec (radius, 90% confidence). We note that the afterglow is slightly blended with the USNO-B1.0 star 274-094527, which makes it dificult to confirm the detection in the b band. Magnitudes and upper limits are reported below. Filter TSTART TSTOP Exposure Mag Err Comment white 113 213 98 18.70 0.09 v 219 619 394 16.60 0.07 b 699 6033 206 19.49 0.15 uncertain detection u 674 5828 216 >20.7 3-sigma upper limit uvw1 650 5623 197 >20.3 3-sigma upper limit uvm2 5218 5418 197 >19.9 3-sigma upper limit uvw2 729 6445 197 >20.5 3-sigma upper limit The above magnitudes are not corrected for the Galactic extinction corresponding to a reddening of E_{B-V} = 0.05 mag (Schlegel et al., 1998, ApJS, 500, 525). The photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383,627). The possible detection in the b filter, coupled with the non-detections in the u, uvw1, uvm2, and uvw2 filters, are consistent with a redshift of approximately z < 3.3. The power-law decay index in the v band between 763 and 6505 s is -0.88.