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GCN Circular 22375

Subject
GRB 180204A: Swift detection of a short burst
Date
2018-02-04T02:58:47Z (6 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
K. L. Page (U Leicester), A. P. Beardmore (U Leicester),
A. Deich (PSU), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), A. Tohuvavohu (PSU) and T. N. Ukwatta (LANL)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 02:36:16 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180204A (trigger=808483).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 330.118, +30.846 which is 
   RA(J2000) = 22h 00m 28s
   Dec(J2000) = +30d 50' 45"
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 1.5 sec.  The peak count rate
was ~17000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 02:37:43.8 UT, 87.2 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 330.13359, 30.83807 which is equivalent
to:
   RA(J2000)  = 22h 00m 32.06s
   Dec(J2000) = +30d 50' 17.1"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 56 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.  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
0.10. 

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/too.html.)
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