TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3745 SUBJECT: GRB 050802: Swift/UVOT optical and UV detections DATE: 05/08/03 15:37:09 GMT FROM: Katie McGowan at MSSL-UCL K. McGowan (UCL-MSSL), A. Morgan (PSU), K. Mason (PPARC), T. Kennedy (UCL-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). In addition to our reported detection from the initial V filter observations (McGowan et al., GCN 3739), we now report that we detect the afterglow in all six filters. We extracted data using a 6 arcsec radius aperture centered on the source position (McGowan et al., GCN 3739) for the optical filters, a 12 arcsec radius for the W1 and M2 filters, and 4 arcsec for the W2 filter. If the significance of the source detection was less than 2 sigma we determined a 3-sigma limiting magnitude. The detection in UVW2 implies that the Lyman Limit must be blueward of 2000 A, and we estimate that the burst is at redshift z < 1.2. We obtain the following photometry of the afterglow candidate: Filter Exposure (s) T_mid (s) Magnitude Notes V 100 336 17.07+/-0.09 detection V 900 12566 20.35+/-0.09 detection B 10 437 17.66+/-0.20 detection B 900 36405 21.10+/-0.08 detection U 10 423 16.82+/-0.24 detection U 899.79 35498 20.22+/-0.16 detection W1 10 409 17.08+/-0.29 detection W1 100 2296 19.22+/-0.23 detection M2 278 1316 18.79+/-0.26 detection M2 3753 28197 21.30+/-0.26 detection W2 268 1240.5 20.73+/-0.27 detection W2 3481 25890.5 >22.64 3-sig limit where T_mid is the midpoint of the exposure post-trigger in seconds. The magnitudes are based on preliminary zero points, measured in orbit, and will require refinement with further calibration.