TITLE: GCN CIRCULAR NUMBER: 16819 SUBJECT: GRB 140916A: Swift detection of a burst DATE: 14/09/16 10:58:29 GMT FROM: Judith Racusin at GSFC J. L. Racusin (NASA/GSFC), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), D. Malesani (DARK/NBI) and K. L. Page (U Leicester) report on behalf of the Swift Team: At 10:43:47 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 140916A (trigger=612804). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 40.405, -39.711 which is RA(J2000) = 02h 41m 37s Dec(J2000) = -39d 42' 38" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This is an image trigger so details of the lightcurve can not yet be determined. The XRT began observing the field at 10:46:18.3 UT, 150.8 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 40.39910, -39.68686 which is equivalent to: RA(J2000) = 02h 41m 35.78s Dec(J2000) = -39d 41' 12.7" with an uncertainty of 3.8 arcseconds (radius, 90% containment). This location is 87 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. No spectrum from the promptly downlinked event data is yet available to determine the column density. The initial flux in the 2.5 s image was 1.26e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 160 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. 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 0.01. Burst Advocate for this burst is J. L. Racusin (judith.racusin AT 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.)