TITLE: GCN CIRCULAR NUMBER: 15627 SUBJECT: GRB 131229A: Swift detection of a burst DATE: 13/12/29 06:55:46 GMT FROM: Scott Barthelmy at NASA/GSFC M. J. Page (UCL-MSSL), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC), H. A. Krimm (CRESST/GSFC/USRA), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 06:39:24 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 131229A (trigger=582374). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 85.236, -4.431 which is RA(J2000) = 05h 40m 57s Dec(J2000) = -04d 25' 52" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows multiple peaks with a total duration of about 25 sec. The peak count rate was ~27,000 counts/sec (15-350 keV), at ~13 sec after the trigger. The XRT began observing the field at 06:40:57.9 UT, 93.8 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 85.2327, -4.3962 which is equivalent to: RA(J2000) = +05h 40m 55.85s Dec(J2000) = -04d 23' 46.3" with an uncertainty of 5.0 arcseconds (radius, 90% containment). This location is 125 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 3.18e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U 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. No correction has been made for the expected extinction corresponding to E(B-V) of 0.29. Burst Advocate for this burst is M. J. Page (m.page AT ucl.ac.uk). 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.)