TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3537 SUBJECT: Swift/UVOT observations of GRB050607 DATE: 05/06/08 10:58:45 GMT FROM: Alexander Blustin at MSSL-UCL Ivanushkina, M., Retter, A. (PSU), McGowan, K., Blustin, A. (MSSL), Gehrels, N. (NASA/GSFC) on behalf of the Swift UVOT team The Swift Ultra-Violet/Optical Telescope (UVOT) began observations of GRB050607 on June 7, 2005 at 22:36:23 UT, ~12 hours and 25 minutes after the initial Swift BAT trigger (Retter et al., GCN 3525) as an uploaded ToO. Immediate data from UVOT were not available due to the instrument being in an engineering mode. No optical counterpart is detected at the afterglow position (Rhoads, GCN 3527) in summed images from any filter down to the following 3-sigma upper limits: Filter 3-sig UL Exposure (s) T_mid (s) V 20.21 2036 51530 B 20.95 897 46942 U 20.18 771 42806 UVW1 20.95 900 41963 UVM2 21.33 1482 46727 UVW2 21.30 900 47844 Where T_mid is the mid-time of the summed exposure in seconds after the BAT trigger. The magnitudes are based on preliminary zero-points, measured in orbit, and will require refinement with further calibration.