TITLE: GCN CIRCULAR NUMBER: 20179 SUBJECT: GRB 161117A: Swift detection of a burst with an optical counterpart DATE: 16/11/17 01:46:55 GMT FROM: Scott Barthelmy at NASA/GSFC J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), V. D'Elia (ASDC), J. A. Kennea (PSU), H. A. Krimm (CRESST/NSF/USRA), F. E. Marshall (NASA/GSFC) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 01:35:36 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 161117A (trigger=722604). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 322.070, -29.629 which is RA(J2000) = 21h 28m 17s Dec(J2000) = -29d 37' 43" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows several bright peaks with a total duration of about 160 sec. The peak count rate was ~8000 counts/sec (15-350 keV), at ~110 sec after the trigger. The XRT began observing the field at 01:36:37.5 UT, 60.8 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 322.0530, -29.6119 which is equivalent to: RA(J2000) = +21h 28m 12.72s Dec(J2000) = -29d 36' 42.8" with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 81 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 8.04e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 69 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 21:28:12.53 = 322.05219 DEC(J2000) = -29:36:48.9 = -29.61358 with a 90%-confidence error radius of about 0.62 arc sec. This position is 6.6 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.40 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.06. Burst Advocate for this burst is J. R. Cummings (jayc 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.)