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GCN Circular 29112

Subject
GRB 201221D: Swift detection of a bright short burst
Date
2020-12-21T23:16:01Z (3 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
K. L. Page (U Leicester), S. D. Barthelmy (GSFC), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
B. Sbarufatti (PSU), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 23:06:34 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 201221D (trigger=1014037).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 171.049, +42.144 which is 
   RA(J2000) = 11h 24m 12s
   Dec(J2000) = +42d 08' 39"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 0.3 sec.  The peak count rate
was ~9000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 23:08:01.7 UT, 87.4 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 171.05873, 42.14332 which is equivalent
to:
   RA(J2000)  = 11h 24m 14.10s
   Dec(J2000) = +42d 08' 36.0"
with an uncertainty of 5.7 arcseconds (radius, 90% containment). This
location is 26 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.  We
cannot determine whether the source is fading at the present time. No
spectrum from the promptly downlinked event data is yet available to
determine the column density. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 92 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 100% 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
0.02. 

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 
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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