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GCN Circular 15384

Subject
Swift Trigger 575905: a possible GRB
Date
2013-10-26T07:03:54Z (10 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
S. B. Cenko (GSFC), S. T. Holland (STScI), L. Izzo (URoma/ICRA),
K. L. Page (U Leicester), D. M. Palmer (LANL),
B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf
of the Swift Team:

At 06:39:32 UT, the Swift Burst Alert Telescope (BAT) and located 
a possible GRB in an image trigger (trigger=575905).  Swift slewed 
immediately to the location. 
The BAT on-board calculated location is 
RA, Dec 15.547, +32.487 which is 
   RA(J2000) = 01h 02m 11s
   Dec(J2000) = +32d 29' 13"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual for an image trigger, there
is no obvious variation in the BAT lightcurve. 

The XRT began observing the field at 06:41:33.9 UT, 121.1 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White 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 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
0.07. 

Because the BAT image peak is of marginal significance (7.06 sigma)
and because there is only 2.5 seconds of XRT data immediately
available, which does not show a counterpart, we cannot yet confirm
or deny the reality of this possible GRB.  A final determination
of the nature of this trigger will require the full set of
downlinked data. 

Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov). 
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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