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GCN Circular 32585

Subject
GRB 220926A: Swift detection of a burst
Date
2022-09-26T10:04:24Z (a year ago)
From
Kim Page at U.of Leicester <kimlpage1978@gmail.com>
M. J. Moss (GWU), R. Brivio (INAF-OAB), S. Dichiara (PSU),
M. Ferro (INAF-OAB), N. P. M. Kuin (UCL-MSSL),
K. L. Page (U Leicester), T. M. Parsotan (GSFC/UMBC/CRESSTII),
T. Sbarrato (INAF-OAB) and B. Sbarufatti (INAF-OAB) report on behalf
of the Neil Gehrels Swift Observatory Team:

At 09:22:50 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 220926A (trigger=1125354).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 245.011, -16.043 which is 
   RA(J2000) = 16h 20m 03s
   Dec(J2000) = -16d 02' 32"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 40 sec.  The peak count rate
was ~400 counts/sec (15-350 keV), at ~5 sec after the trigger. 
The source is not well identified in the rate data which is typical 
of an image trigger. 

The XRT began observing the field at 09:25:04.4 UT, 134 seconds
after the BAT trigger. XRT found a bright, uncatalogued X-ray
source located at RA, Dec 245.0022, -16.0438 which is equivalent to:
   RA(J2000)  = 16h 20m 0.53s
   Dec(J2000) = -16d 02' 37.7"
with an uncertainty of up to 2 arcmin (radius, 90% containment). 
Given the star tracker loss of lock at the time of the trigger, it is 
unclear how accurate this localisation is, hence the large uncertainty 
listed.  No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 143 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 of no aspect solution. Results from the list of sources
generated on-board are not available at this time. No correction has been made
for the expected extinction corresponding to E(B-V) of 0.269. 

Note that this trigger occurred during an interval when the star
trackers had lost lock. However, we believe this to be a real GRB. 

Burst Advocate for this burst is M. J. Moss (mikejmoss3 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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