TITLE: GCN CIRCULAR NUMBER: 13727 SUBJECT: GRB 120909A: Swift detection of a burst DATE: 12/09/09 01:54:56 GMT FROM: David Palmer at LANL S. Immler (CRESST/GSFC/UMD), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU), S. T. Holland (STScI), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 01:42:03 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 120909A (trigger=533060). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 275.685, -59.426 which is RA(J2000) = 18h 22m 44s Dec(J2000) = -59d 25' 34" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows one, possibly two, peaks with a duration of about 5 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 01:43:36.6 UT, 93.4 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 275.7388, -59.4485 which is equivalent to: RA(J2000) = +18h 22m 57.31s Dec(J2000) = -59d 26' 54.6" with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 127 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 7.55e-09 erg cm^-2 s^-1 (0.2-10 keV). Because of an earth limb constraint, Swift slewed away before UVOT could take its initial exposures. Subsequent orbits will include UVOT observations. Burst Advocate for this burst is S. Immler (stefan.immler AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)