TITLE: GCN CIRCULAR NUMBER: 22433 SUBJECT: GRB 180222A: Swift detection of a burst DATE: 18/02/22 13:37:12 GMT FROM: Scott Barthelmy at NASA/GSFC J. K. Cannizzo (NASA/UMBC), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), P. A. Evans (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC), Z. Liu (NAOC/U. Leicester), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), M. H. Siegel (PSU) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 13:10:03 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180222A (trigger=811235). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 256.571, -36.803, which is RA(J2000) = 17h 06m 17s Dec(J2000) = -36d 48' 08" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single FRED-like peak with a duration of about 25 sec. The peak count rate was ~1400 counts/sec (15-350 keV), at ~2 sec after the trigger. The XRT began observing the field at 13:11:22.7 UT, 79.2 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 256.54119, -36.80929 which is equivalent to: RA(J2000) = 17h 06m 09.89s Dec(J2000) = -36d 48' 33.4" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 88 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 (6.65 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 7.9 (+11.04/-4.96) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 82 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 97% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the large, but uncertain, extinction expected. Burst Advocate for this burst is J. K. Cannizzo (cannizzo AT milkyway.gsfc.nasa.gov). 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.)