GCN Circular 8198

S. T. Holland (CRESST/USRA/GSFC) & L. Vetere (PSU) report on behalf of
the Swift/UVOT team:

       The Swift/UVOT observed the field of GRB 080906 starting 62 s
after the BAT trigger (Vetere et al., 2008, GCNC. 8186).  Settled
observations started at T + 82 s.  We detect the optical afterglow
(Vetere et al., GCNC 8186) in the v, b, u, and white filters.  The
refined UVOT source position is

  RA (J2000.0) =  15:12:10.65
Dec (J2000.0) = -80:31:03.2

with an estimated uncertainty of 0.64 arcsec (radius, 90% confidence).

     Magnitudes and upper limits are reported below.

Filter   TSTART   TSTOP   Exposure     Mag  Err  Comment
  white       82     182         98   19.71 0.15
    v        188     588        393   18.61 0.12
    b        668    6204        216   21.02 0.44
    u        643    5998        236   20.37 0.34
   uvw1      619    5793        236  >20.9        2-sigma upper limit
   uvm2      594    5588        236  >20.5        2-sigma upper limit
   uvw2      698    6614        235  >21.1        2-sigma upper limit

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.30 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 detection in the u filter, coupled with the non-detections in
the uvw1, uvm2, and uvw2 filters, are consistent with a redshift of
approximately z < 2.6.  The power-law decay index in the v band
between 338 and 6719 s is -0.50 +/- 0.04.

Please update my e-mail address in your Address Book to <Stephen.T.Holland@nasa.gov 
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