TITLE: GCN CIRCULAR NUMBER: 20423 SUBJECT: GRB 170111A: Swift detection of a burst DATE: 17/01/11 00:53:54 GMT FROM: David Palmer at LANL A. P. Beardmore (U Leicester), D. N. Burrows (PSU), C. Gronwall (PSU), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 00:33:28 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 170111A (trigger=731887). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 20.717, -32.540 which is RA(J2000) = 01h 22m 52s Dec(J2000) = -32d 32' 23" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single peak structure with a duration of about 40 sec. The peak count rate was ~700 counts/sec (15-350 keV), at ~2 sec after the trigger. The XRT began observing the field at 00:35:14.8 UT, 106.7 seconds after the BAT trigger. Using promptly downlinked data we find a variable, uncatalogued X-ray source with an enhanced position: RA, Dec 20.6981, -32.5653 which is equivalent to: RA(J2000) = 01h 22m 47.56s Dec(J2000) = -32d 33' 55.1" with an uncertainty of 2.1 arcseconds (radius, 90% containment). This location is 107 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 in excess of the Galactic value (3.10 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.1 (+2.60/-2.25) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 112 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 approximately 70% 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 0.03. Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.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.)