TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3167 SUBJECT: GRB 050402: Early observations with Swift-UVOT DATE: 05/04/02 08:02:08 GMT FROM: Patricia Schady at MSSL/Swift S. T. Holland, M. Still (GSFC/USRA), W. Landsman (GSFC), Adam Morgan, S. Hunsberger (PSU), A. Breeveld (MSSL), P. Roming (PSU), K. Mason, P. Schady (MSSL), M. Ivanushkina (PSU), T. Poole (MSSL), C. Gronwall (PSU), A. Blustin (MSSL), P. Brown (PSU), S. Rosen, K. McGowan, M. De Pasquale (MSSL), P.Boyd, S. T. Holland (GRFC/UMBC), H. Huckle (MSSL), P. Broos (PSU), T. Kennedy, P. Smith, B. Hancock (MSSL), H. Krimm (GSFC/USRA), S. Kock (PSU), M. Carter (MSSL), K. Gendreau (GSFC), M.Chester (PSU), D. Hinshaw (GSFC/SPSYS), J. Nousek (PSU), N. Gehrels (GSFC), on behalf of the Swift UVOT team. The Swift Ultra-Violet/Optical Telescope (UVOT) began observing the field of GRB 050402 at 06:12:01.6 UT, approximately 125 seconds after the BAT trigger. The first image was sent down via the TDRSS link approximately 300 seconds after the trigger. This image was a 100 second exposure taken with the V filter. It was centred on the BAT position, and had a size of 5 x 5 arcminutes, which covered 88% of the BAT error circle. The image was binned 8 x 8 to reduce the bandwidth required for transmission. A comparison against the DSS showed no new sources down to a 5-sigma limiting magnitude of approximately V = 18.84 +/- 0.09 , based on preliminary in-orbit zero points.