TITLE: GCN CIRCULAR NUMBER: 18979 SUBJECT: GRB 160203A: Swift detection of a burst DATE: 16/02/03 02:34:26 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT P. D'Avanzo (INAF-OAB), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 02:13:10 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 160203A (trigger=672525). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 161.952, -24.762, which is RA(J2000) = 10h 47m 48s Dec(J2000) = -24d 45' 43" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows several overlapping peaks with a duration of about 25 sec. The peak count rate was ~500 counts/sec (15-350 keV), at ~5 sec after the trigger. The XRT began observing the field at 02:15:27.8 UT, 137.3 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 161.9511, -24.7887 which is equivalent to: RA(J2000) = 10h 47m 48.27s Dec(J2000) = -24d 47' 19.2" with an uncertainty of 2.3 arcseconds (radius, 90% containment). This location is 96 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 consistent with the Galactic value of 7.41 x 10^20 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 150 seconds with the White filter starting 139 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 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 0.07. Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo AT brera.inaf.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.)