[vsnet-grb-info 2121] GRB050908: detection of Swift/UVOT optical counterpart

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3960
SUBJECT: GRB050908: detection of Swift/UVOT optical counterpart
DATE:    05/09/10 21:09:41 GMT
FROM:    Alexander Blustin at MSSL-UCL  <ajb at mssl.ucl.ac.uk>

M. De Pasquale (UCL-MSSL), M. Goad (U. Leicester), A. J. Blustin
(UCL-MSSL), M. Chester (PSU), L. Angelini (GSFC-JHU),
N. Gehrels (GSFC) on behalf of the Swift/UVOT team

Further analysis of the early Swift/UVOT data for GRB050908
(Goad et al., GCN 3942) reveals a faint, decaying source at the
position of the optical counterpart reported by Torii (GCN 3943).

In summed V-band images taken between 104-650 s after the trigger,
a source is visible at 19.3 +/0.1 mag in a total exposure time of
149 s. It is not detected in data taken later than this; in summed
V-band images from 700-40650 s post-trigger a 3-sigma upper limit of
20.5 mag is obtained at the same position in 2296 s of co-added
exposure time. The source is only detected in the V band.

These magnitudes are uncorrected for extinction and are based on
preliminary zero-points, measured in orbit, and will require
refinement with further calibration.