TITLE: GCN CIRCULAR NUMBER: 20008 SUBJECT: GRB 161007A: Swift detection of a burst DATE: 16/10/07 21:40:54 GMT FROM: David Palmer at LANL V. D'Elia (ASDC), L. M. Z. Hagen (PSU), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team: At 21:25:43 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 161007A (trigger=716127). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 103.390, +23.289 which is RA(J2000) = 06h 53m 34s Dec(J2000) = +23d 17' 20" 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 60 sec. The peak count rate was ~600 counts/sec (15-350 keV), at ~30 sec after the trigger. The XRT began observing the field at 21:27:47.8 UT, 124.9 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 103.40706, 23.30639 which is equivalent to: RA(J2000) = 06h 53m 37.69s Dec(J2000) = +23d 18' 23.0" with an uncertainty of 4.3 arcseconds (radius, 90% containment). This location is 84 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. 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 1.56e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 133 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 0.12. Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.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.)