GCN Circular 3838

M. Chester (PSU), M. Page (UCL-MSSL), P. Roming (PSU),
F. Marshall (GSFC), P. Boyd (GSFC), L. Angelini (GSFC-JHU),
J. Greiner (MPE), N. Gehrels (GSFC), on behalf of the Swift UVOT team.


Swift/UVOT began observing GRB050820 at 06:36:13 UT.
The initial 100-second finding chart exposure in V was cut short
due to entry into the SAA; it was repeated on the second orbit.


The afterglow is detected in the V, B, U, and one UV band.
Similar to the ground-based observations (GCN #3829),
UVOT sees a rising, then falling, light curve in V.
Analysis in the other bands is continuing.


V-band Observations:
Time-Since-Trigger       V
   80 s               18.2 +/- 0.3
 4635 s               17.6 +/- 0.2
12238 s               18.2 +/- 0.2


Other:
Time-Since-Trigger    Mag               Filter
 5647 s                18.3 +/- 0.2       U
10423 s                19.0 +/- 0.1       B
 4741 s                20.4 +/- 0.2       UVW1
11331 s               >21.0               UVW2


The magnitudes have not been corrected for extinction.
Upper limits are given at the 5-sigma level.