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GCN Circular 32060

Subject
GRB 220518A: Swift detection of a burst
Date
2022-05-18T06:47:24Z (3 years ago)
From
Kim Page at U.of Leicester <kimlpage1978@gmail.com>
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/)
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