TITLE: GCN CIRCULAR NUMBER: 15490 SUBJECT: GRB 131117A: Swift detection of a burst DATE: 13/11/17 00:43:57 GMT FROM: David Palmer at LANL M. J. Page (UCL-MSSL), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC), C. J. Mountford (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL) and C. A. Swenson (PSU) report on behalf of the Swift Team: At 00:34:04 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 131117A (trigger=577968). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 332.339, -31.722 which is RA(J2000) = 22h 09m 21s Dec(J2000) = -31d 43' 19" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 20 sec. The peak count rate was ~1750 counts/sec (15-350 keV), at ~4 sec after the trigger. The XRT began observing the field at 00:35:10.8 UT, 66.1 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 332.33119, -31.76055 which is equivalent to: RA(J2000) = 22h 09m 19.49s Dec(J2000) = -31d 45' 38.0" with an uncertainty of 3.9 arcseconds (radius, 90% containment). This location is 140 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. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 1.41 x 10^20 cm^-2 (Kalberla et al. 2005). UVOT took a finding chart exposure of 150 seconds with the White filter starting 69 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 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 0.02. 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.)