TITLE: GCN CIRCULAR NUMBER: 12559 SUBJECT: GRB 111117A: Swift detection of a short hard burst DATE: 11/11/17 12:27:17 GMT FROM: David Burrows at PSU/Swift V. Mangano (INAF-IASFPA), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), S. Campana (INAF-OAB), J. R. Cummings (NASA/UMBC), V. D'Elia (ASDC), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC), H. A. Krimm (CRESST/GSFC/USRA), O. M. Littlejohns (U Leicester), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester), S. R. Oates (UCL-MSSL), C. Pagani (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), E. Sonbas (GSFC/USRA/Adiyaman Univ.), R. L. C. Starling (U Leicester), C. A. Swenson (PSU) and E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team: At 12:13:41 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 111117A (trigger=507901). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 12.702, +23.021 which is RA(J2000) = 00h 50m 49s Dec(J2000) = +23d 01' 16" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a double-peaked structure with a duration of about 0.6 sec. The peak count rate was ~6140 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 12:14:58.7 UT, 76.8 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 12.6925, 23.0103 which is equivalent to: RA(J2000) = 00h 50m 46.19s Dec(J2000) = +23d 00' 36.9" with an uncertainty of 2.6 arcseconds (radius, 90% containment). This location is 50 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. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (3.70 x 10^20 cm^-2, Kalberla et al. 2005), with an excess column of 3 (+2.73/-2.30) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 250 seconds with the U filter starting 136 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 19.2 mag. 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 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.03. Burst Advocate for this burst is V. Mangano (vanessa 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.)