TITLE: GCN CIRCULAR NUMBER: 7147 SUBJECT: GRB 071227: Swift detection of a burst DATE: 07/12/27 20:36:40 GMT FROM: Takanori Sakamoto at NASA/GSFC T. Sakamoto (NASA/UMBC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), M. M. Chester (PSU), S. D. Hunsberger (PSU), K. L. Page (U Leicester), J. L. Racusin (PSU), P. Romano (Univ. Bicocca & INAF-OAB), G. Sato (GSFC/ISAS), B. Sbarufatti (INAF-IASFPA), M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester), E. Troja (INAF-IASFPA) and D. E. Vanden Berk (PSU) report on behalf of the Swift Team: At 20:13:47 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 071227 (trigger=299787). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 58.120, -55.953 which is RA(J2000) = 03h 52m 29s Dec(J2000) = -55d 57' 08" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed at least three spikes with a duration of about 5 sec. The peak count rate was ~4500 counts/sec (15-350 keV), at ~0.5 sec after the trigger. The XRT began observing the field at 20:15:06 UT, 79 seconds after the BAT trigger. From prompt downlinked data, XRT found a variable, uncatalogued X-ray source located at RA, Dec 58.1316, -55.9833 which is RA(J2000) = 03h 52h 31.58s Dec(J2000) = -55d 58' 59.9" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 112 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 9.6e-10 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 86 seconds after the BAT trigger, and a second finding chart of 400 seconds in V starting 192 seconds after the trigger. No 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 3-sigma upper limit at the XRT position is 19.9 mag in White, 19.0 in V. 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 extinction corresponding to E(B-V) = 0.01. Burst Advocate for this burst is T. Sakamoto (takanori AT milkyway.gsfc.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.)