TITLE: GCN CIRCULAR NUMBER: 18926 SUBJECT: GRB 160123A: Swift detection of a burst DATE: 16/01/23 09:18:57 GMT FROM: Boris Sbarufatti at INAF-OAB/IASFPA D. Malesani (DARK/NBI), S. D. Barthelmy (GSFC), T. Sakamoto (AGU) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team: At 08:58:20 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 160123A (trigger=671447). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 150.286, -33.779 which is RA(J2000) = 10h 01m 09s Dec(J2000) = -33d 46' 43" 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 25 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 08:59:38.1 UT, 78.0 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 150.3125, -33.7754 which is equivalent to: RA(J2000) = 10h 01m 14.99s Dec(J2000) = -33d 46' 31.3" with an uncertainty of 2.1 arcseconds (radius, 90% containment). This location is 80 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 (1.31 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 2.9 (+2.66/-2.30) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 250 seconds with the U filter starting 295 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 0.10. Burst Advocate for this burst is D. Malesani (malesani AT dark-cosmology.dk). 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.)