[vsnet-grb-info 6483] GRB 080810: Swift/UVOT Refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8095
SUBJECT: GRB 080810: Swift/UVOT Refined Analysis
DATE:    08/08/11 17:31:57 GMT
FROM:    Stephen Holland at USRA/NASA/GSFC/SSC  <sholland at milkyway.gsfc.nasa.gov>

S. T. Holland (CRESST/USRA/GSFC) & K. L. Page (U Leicester) report on
behalf of the Swift/UVOT team:

      The Swift/UVOT observed the field of GRB 080810 starting 65 s
after the BAT trigger (Page et al., GCNC. 8080).  Settled observations
started at T + 85 s.  We detect the optical afterglow (Page et al.,
GCNC 8080) in the v, b, and white filters at the UVOT-enhanced
location of the XRT afterglow (Evans et al., 2008, GCNC 8086).  The
refined UVOT source position is

  RA (J2000.0) =  23:47:10.26
Dec (J2000.0) = +00:19:11.3

with an estimated uncertainty of +/-0.6 arcsec (radius, 90%
confidence).  This is consistent with the positions of the optical
afterglow reported by Rykoff (GCNC 8084) and de Ugarte Postigo (GCNC
8089)

    Magnitudes and upper limits are reported below.

Filter     T_start (s) T_stop  Exposure      Mag  Err  Comment
white           85        185        98     14.63 0.07
   v            191        459       264     14.06 0.06
   b           4432       4632       197     17.85 0.08
   u           4227     68,686       727    >21.4       3-sigma UL
  uvw1         4022     68,283      3099    >22.3       3-sigma UL
  uvm2         3817     62,540      3229    >22.2       3-sigma UL
  uvw2         4843     50,866      1510    >22.0       3-sigma UL

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.03 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
non-detections in the u, uvw1, uvm2, and uvw2 filters are consistent
with a redshift of z = 3.35 (Prochaska, GCNC 8083).  The power-law
decay index in the b band between 4532 and 27,387 s is -1.29 +/- 0.22.