GCN Circular 8192

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.