TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3525 SUBJECT: GRB050607: Swift Detection of a long GRB DATE: 05/06/07 12:07:33 GMT FROM: Alon Retter at PSU A. Retter, J. Racusin, J. Kennea, D. Burrows (PSU), D. Palmer (LANL), K. McGowan (MSSL), J. Cummings (NRC/GSFC), S. Barthelmy, N. Gehrels (GSFC) on behalf of the Swift Team report: At 09:11:23 UT the Swift-BAT triggered on GRB 050607 (trigger 132247). The BAT refined ground position is RA, Dec 300.167, +9.137 (J2000) {20h00m40s, +09d 08' 13"}. The burst had 3 peaks over 30 seconds, with a T90 of 26.5 seconds from T+0 to T+26.5 seconds. Its spectrum is well fit by a simple power law with an index of 1.93 +/- 0.14. The total fluence was (8.9 +/- 1.2) x 10^-7 erg/cm2 over 15-350 keV. The peak flux was 1.15+/-0.16 photons/cm2/s from T+1 to T+2 seconds. The burst was 27 degrees off the BAT boresight in the 87% coded field of view. Swift slewed to the position of the burst immediately, starting 17 seconds after the burst trigger. The XRT was pointed promptly at the burst at 09:13:02 UT (100 s after the BAT burst trigger). The XRT did not centroid on-board, but ground analysis revealed a bright X-ray source near the center of the field of view, with position RA(J2000) = 20h 00m 42.5s Dec(J2000) = +09d 08' 30'' We estimate an uncertainty of approximately 8 arcseconds radius (90% containment). This position is 40 arcseconds from the BAT position. Immediate data from UVOT will not be available due to the instrument being in an engineering mode.