TITLE: GCN CIRCULAR NUMBER: 32060 SUBJECT: GRB 220518A: Swift detection of a burst DATE: 22/05/18 06:47:24 GMT FROM: Kim Page at U.of Leicester J.D. Gropp (PSU), K. L. Page (U Leicester), T. M. Parsotan (GSFC/UMBC/CRESSTII), B. Sbarufatti (PSU) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 06:19:20 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 220518A (trigger= 1107050). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 55.369, -47.571 which is RA(J2000) = +03h 41m 29s Dec(J2000) = -47d 34' 15" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). There are currently no BAT light curve data available at this time. The XRT began observing the field at 06:21:27.1 UT, 126.4 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 55.34297, -47.58392 which is equivalent to: RA(J2000) = 03h 41m 22.31s Dec(J2000) = -47d 35' 02.1" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 78 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 https://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 (9.33 x 10^19 cm^-2, Willingale et al. 2013), with an excess column of 5 (+3.25/-2.72) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 129 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. No correction has been made for the expected extinction corresponding to E(B-V) of 0.008. Burst Advocate for this burst is J.D. Gropp (jdg44 AT psu.edu). 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/)