TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3838 SUBJECT: Swift/UVOT photometry of GRB050820 DATE: 05/08/20 21:04:12 GMT FROM: Margaret Chester at PSU 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.