TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3157 SUBJECT: GRB 050331: Swift UVOT Source DATE: 05/03/31 19:03:26 GMT FROM: Pete Roming at PSU M. Still (GSFC/USRA), W. Landsman (GSFC), A. Morgan, C. James (MSSL), 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 (GSFC/UMBC), S. T. Holland (GSFC/USRA), M. Carter, H. Huckle (MSSL), P. Broos (PSU), T. Kennedy, P. Smith, B. Hancock (MSSL), S. Koch (PSU), S. Zane (MSSL), 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 settled observations of the field of GRB 050331 (Angelini et al; GCN 3155) at 17:14:09 UT, 135s after the BAT trigger. The first data taken after spacecraft settling was a 100s V image, sent directly to the ground through the TDRSS system, with pixel binning of 8x8 to reduce telemetry. Binned pixel sizes are 4x4 arcsec and the field of view is 5.3x5.3 arcmin. An extremely bright source, consistent with the XRT position, is found in the image. A magnitude can not be determined at this time due to saturation of the detector (13.0 mag).