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GCN Circular 31045

Subject
Swift Trigger 1082569 is probably not a GRB
Date
2021-11-05T11:05:42Z (3 years ago)
From
Kim Page at U.of Leicester <kimlpage1978@gmail.com>
M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB), J.D. Gropp (PSU),
N. J. Klingler (GSFC/UMBC/CRESSTII), A. Melandri (INAF-OAB),
K. L. Page (U Leicester) and T. Sbarrato (INAF-OAB) report on behalf
of the Neil Gehrels Swift Observatory Team:

At 10:27:23 UT, the Swift Burst Alert Telescope (BAT) triggered on an event 
with marginal significance (trigger=1082569).  Swift slewed immediately to 
the location. The BAT on-board calculated location is 
RA, Dec 271.077, +41.399 which is 
   RA(J2000) = 18h 04m 19s
   Dec(J2000) = +41d 23' 55"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve did not show any significant 
features. 

The XRT began observing the field at 10:28:32.0 UT, 68.8 seconds after
the BAT trigger. No source was detected in 1.6 ks of promptly
downlinked data. We are waiting for the full dataset to detect and
localise any XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 71 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 25% of
the BAT 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
BAT 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
0.031. 

Due to the marginal detection significance in both BAT rates and
on-board image, and the lack of detection by XRT, we believe that 
this is probably a noise fluctuation in BAT and  not an
astrophysical event.
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