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GCN Circular 32827

Subject
GRB 221024A: Swift detection of a burst
Date
2022-10-24T13:23:22Z (a year ago)
From
Jamie Kennea at Penn State U <jak51@psu.edu>
R. Brivio (INAF-OAB), P. D'Avanzo (INAF-OAB), M. Ferro (INAF-OAB),
J.D. Gropp (PSU), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
S. Laha (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL),
T. M. Parsotan (GSFC/UMBC/CRESSTII), T. Sbarrato (INAF-OAB),
B. Sbarufatti (INAF-OAB), M. H. Siegel (PSU) and M. A. Williams (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 13:00:27 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 221024A (trigger=1131029).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 169.718, +33.041 which is 
   RA(J2000) = 11h 18m 52s
   Dec(J2000) = +33d 02' 28"
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 30 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 13:02:36.5 UT, 129.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 169.74060, 33.04207 which is equivalent
to:
   RA(J2000)  = 11h 18m 57.74s
   Dec(J2000) = +33d 02' 31.5"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 68 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 (2.86 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4
(+2.22/-1.98) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the UVW2 filter
starting  127 seconds after the BAT trigger. No credible afterglow
candidate has been  found in the initial data products. The 2.7'x2.7'
sub-image processing failed because there is no aspect solution due
to a nearby very bright star.   Results from the list of  sources
generated on-board are not available at this time. 

Burst Advocate for this burst is R. Brivio (riccardo.brivio AT inaf.it). 
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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