TITLE: GCN CIRCULAR NUMBER: 19478 SUBJECT: GRB 160601A: Swift detection of a short hard burst DATE: 16/06/01 15:00:57 GMT FROM: David Palmer at LANL D. Kocevski (NASA/GSFC/ORAU), P.A. Evans (U Leicester), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), B. Mingo (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), T. G. R. Roegiers (PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 14:43:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 160601A (trigger=688452). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 235.034, +64.495 which is RA(J2000) = 15h 40m 08s Dec(J2000) = +64d 29' 41" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 0.2 sec. The peak count rate was ~7000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 14:44:16.3 UT, 74.0 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 234.9351, 64.5401 which is equivalent to: RA(J2000) = 15h 39m 44.43s Dec(J2000) = +64d 32' 24.2" with an uncertainty of 3.3 arcseconds (radius, 90% containment). This location is 223 arcseconds from the BAT onboard position. 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. This position is more than 2-sigma away from the BAT position, and so possibly unrelated to the trigger. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 2.04 x 10^20 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 250 seconds with the U filter starting 78 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 none of the XRT error circle. 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. Burst Advocate for this burst is D. Kocevski (dankocevski AT gmail.com). 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.)