TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3829
SUBJECT: GRB050820: Optical afterglow from P60
DATE:    05/08/20 07:15:30 GMT
FROM:    Derek Fox at PSU  <dfox@astro.psu.edu>

Derek B. Fox (Penn State) and S. Bradley Cenko (Caltech) report on
behalf of a larger collaboration:

"We have observed the BAT/XRT localization region of GRB050820 (Swift
Trigger #151207) with the robotic Palomar 60-inch telescope (P60), in
a series of automated exposures beginning at 06:37 UT, approximately 3
minutes after the burst.

We identify a bright, new, variable point source within the XRT (and
BAT) localization region at coordinates:

    R.A.  22:29:38.11, Dec +19:33:37.1 (J2000)

with coordinate uncertainty <0.5 arcsec relative to USNO-B1.0 catalog
astrometry.  Photometry of the source relative to the USNO-B1.0
catalog indicates that in the R-band it brightens to a peak magnitude
of R~14.7 mag at 7 minutes after the burst and has decayed by 0.4 mag
at 12 minutes after the burst.

We therefore identify the source as the optical afterglow of
GRB050820."