TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3739 SUBJECT: GRB 050802: Swift/UVOT observations DATE: 05/08/02 17:34:24 GMT FROM: Katie McGowan at MSSL-UCL K. McGowan (MSSL), D. Band (GSFC-UMBC), P. Brown, C. Gronwall (PSU), H. Huckle, B. Hancock (MSSL) report on behalf of the Swift/UVOT team: The Swift/UVOT began observing the afterglow of GRB 050802 at 2005-08-02T10:15:14, 286 s after the BAT trigger (Band et al., GCN 3734). We detect the afterglow in the V-band data at a position (J2000, corrected to the DSS coordinates) of: RA 14:37:5.69 (+/- 1 arcsec) Dec +27:47:12.2 (+/- 1 arcsec) The data are extracted using a 6 arcsec radius aperture centered on the source position. If the significance of the source detection was less than 2 sigma we determined a 3-sigma limiting magnitude. Filter Exposure (s) T_mid (s) Magnitude Notes V 100 336 17.07+/-0.09 detection V 10 466 17.32+/-0.20 detection V 10 550 17.10 3-sig limit V 10 634 17.17 3-sig limit V 10 718.5 16.77+/-0.20 detection V 10 803 17.34 3-sig limit V 10 887.5 17.04+/-0.20 detection V 10 972 17.46 3-sig limit V 100 1463 18.35+/-0.09 detection V 100 2088 18.81+/-0.09 detection where T_mid is the midpoint of the exposure post-trigger in seconds. Analysis of the data from the other filters is ongoing. The magnitudes are based on preliminary zero points, measured in orbit, and will require refinement with further calibration.