TITLE: GCN CIRCULAR NUMBER: 6394 SUBJECT: GRB 070509: Swift detection of a burst DATE: 07/05/09 03:17:03 GMT FROM: David Palmer at LANL L. Vetere (PSU), S. D. Barthelmy (GSFC), M. M. Chester (PSU), D. Grupe (PSU), S. T. Holland (CRESST/GSFC/USRA), J. A. Kennea (PSU), C. B. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC), C. Pagani (PSU), D. M. Palmer (LANL), J. L. Racusin (PSU), M. Stamatikos (NASA/ORAU) and D. E. Vanden Berk (PSU) report on behalf of the Swift Team: At 02:48:27 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070509 (trigger=278903). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 237.927, -78.681 which is RA(J2000) = 15h 51m 42s Dec(J2000) = -78d 40' 49" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single FRED-like peak with a duration of about 10 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began taking data at 02:49:35 UT, 68 seconds after the BAT trigger. XRT found a faint, uncatalogued X-ray source. The ground calculated location is RA, Dec 237.9592, -78.6511 which is RA(J2000) = 15h 51m 50.2s Dec(J2000) = -78d 39'04.0" with an uncertainty of 4.6 arcsec (radius, 90% containment, including systematic uncertainty). This location is 1.8 arcmin from the BAT on-board position, within the BAT error circle. UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 72 seconds after the BAT trigger, and a finding chart exposure of 400 seconds in V starting 177 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle; the 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.14.