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GCN Circular 32925

Subject
GRB 221110A: Swift detection of a burst with an optical counterpart
Date
2022-11-10T02:57:59Z (2 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
M. A. Williams (PSU), S. Dichiara (PSU), J. A. Kennea (PSU),
S. Laha (GSFC/UMBC), D. M. Palmer (LANL) and A. Tohuvavohu (U Toronto)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 02:28:17 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 221110A (trigger=1136936).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 29.119, -27.314 which is 
   RA(J2000) = 01h 56m 29s
   Dec(J2000) = -27d 18' 50"
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 10 sec.  The peak count rate
was ~1400 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 02:29:32.8 UT, 75.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 29.09928, -27.29435 which
is equivalent to:
   RA(J2000)  = 01h 56m 23.83s
   Dec(J2000) = -27d 17' 39.7"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 94 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 (1.46 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.2
(+3.14/-2.70) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 80 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	01:56:23.90 =  29.09958
  DEC(J2000) = -27:17:36.9  = -27.29355
with a 90%-confidence error radius of about 0.5 arc sec. This position is 3.0
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.62 with a 1-sigma error of about  0.07. 

Burst Advocate for this burst is M. A. Williams (mjw6837 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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