TITLE: GCN CIRCULAR NUMBER: 13822 SUBJECT: GRB 120927A: Swift detection of a burst DATE: 12/09/27 23:05:47 GMT FROM: David Burrows at PSU/Swift A. Maselli (INAF-IASFPA), W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC), V. D'Elia (ASDC), S. T. Holland (STScI), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), V. Mangano (INAF-IASFPA), C. B. Markwardt (NASA/GSFC) and F. E. Marshall (NASA/GSFC) report on behalf of the Swift Team: At 22:40:46 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 120927A (trigger=534815). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 136.600, +0.417 which is RA(J2000) = 09h 06m 24s Dec(J2000) = +00d 25' 02" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a broad single-peaked structure with a duration of about 50 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 22:43:20.0 UT, 154 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 136.614125, 0.415722 which is equivalent to: RA(J2000) = 09h 06m 27.20s Dec(J2000) = +00d 24' 56.6" with an uncertainty of 3.6 arcseconds (radius, 90% containment). This location is 52 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. UVOT took a finding chart exposure of 150 seconds with the White filter starting 158 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the BAT and XRT error circles. 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 0.04. Burst Advocate for this burst is A. Maselli (maselli AT ifc.inaf.it). 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.)