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GCN Circular 32076

Subject
GRB 220521A: Swift detection of a burst
Date
2022-05-21T23:31:51Z (2 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
S. Dichiara (PSU), J.D. Gropp (PSU), D. M. Palmer (LANL) and
B. Sbarufatti (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 23:20:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 220521A (trigger=1107466).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 275.197, +10.384 which is 
   RA(J2000) = 18h 20m 47s
   Dec(J2000) = +10d 23' 03"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 15 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 23:21:57.7 UT, 96.3 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 275.22891, 10.37262 which is equivalent
to:
   RA(J2000)  = 18h 20m 54.94s
   Dec(J2000) = +10d 22' 21.4"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 120 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 consistent with the Galactic value of 1.87
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 99 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. Results from the 2.7'x2.7' sub-image
are not available at this time. 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 0.185. 

Burst Advocate for this burst is S. Dichiara (simonedichiara55 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/)
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