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GCN Circular 19135

Subject
Swift possibly triggered on IGR17091-3624
Date
2016-03-03T23:09:19Z (8 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
S. D. Barthelmy (GSFC) and K. L. Page (U Leicester) report on behalf
of the Swift Team:

At 22:40:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located IGR17091-3624 (trigger=677582).  Swift was already observing this source. 
The BAT on-board calculated location is 
RA, Dec 257.217, -36.401, which is 
   RA(J2000)  =  17h 08m 52s
   Dec(J2000) = -36d 24' 02"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is typical for image triggers (6 min in this case),
the light curve does not show anything significant except for two brief
peaks (each ~10 sec long) separated by ~450 sec. These peaks could easily be due
to a noisy detector.  We will not be able to say until the full data has been
downloaded and a mask-weight light curve generated. The peak count rate
was ~300 counts/sec (15-350 keV). 

No source was detected in the 2.5-s promptly available image, taken 434.s seconds 
after the BAT trigger. 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 438 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 large, but uncertain extinction expected.
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