[vsnet-grb-info 14176] GRB 131117A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15490
SUBJECT: GRB 131117A: Swift detection of a burst
DATE:    13/11/17 00:43:57 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

M. J. Page (UCL-MSSL), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), C. J. Mountford (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL) and C. A. Swenson (PSU)
report on behalf of the Swift Team:

At 00:34:04 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 131117A (trigger=577968).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 332.339, -31.722 which is 
   RA(J2000) = 22h 09m 21s
   Dec(J2000) = -31d 43' 19"
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 20 sec.  The peak count rate
was ~1750 counts/sec (15-350 keV), at ~4 sec after the trigger. 

The XRT began observing the field at 00:35:10.8 UT, 66.1 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 332.33119, -31.76055 which
is equivalent to:
   RA(J2000)  = 22h 09m 19.49s
   Dec(J2000) = -31d 45' 38.0"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 140 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 consistent with the Galactic value of 1.41
x 10^20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 69 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 none of
the XRT error circle. 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 0.02. 

Burst Advocate for this burst is M. J. Page (m.page AT ucl.ac.uk). 
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.)