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GCN Circular 20182

Subject
GRB 161117B: Swift detection of a burst
Date
2016-11-17T10:04:47Z (7 years ago)
From
Mike Siegel at PSU/Swift MOC <siegel@swift.psu.edu>
E. Troja (NASA/GSFC/UMCP), A. D'Ai (INAF-IASFPA), V. D'Elia (ASDC),
P.A. Evans (U Leicester), H. A. Krimm (CRESST/NSF/USRA),
K. L. Page (U Leicester), B. Sbarufatti (INAF-OAB/PSU) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 09:49:43 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 161117B (trigger=722642).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 298.855, -67.707 which is 
   RA(J2000) = 19h 55m 25s
   Dec(J2000) = -67d 42' 23"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed am initial weak peak
near the trigger time followed by stronger emission starting about 100
seconds later.  The total duration is about 150 sec.  The peak count rate
was ~4500 counts/sec (15-350 keV), at ~135 sec after the trigger. 

The XRT began observing the field at 09:50:58.0 UT, 74.4 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
298.8244, -67.7029 which is equivalent to:
   RA(J2000)  = 19h 55m 17.85s
   Dec(J2000) = -67d 42' 10.6"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 44 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 http://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 (6.49 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.3
(+2.89/-2.47) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 4.69e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 82 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 100% of
the XRT 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
XRT 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
0.10. 

Burst Advocate for this burst is E. Troja (eleonora.troja 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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