[vsnet-grb-info 18826] GRB 161217A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20276
SUBJECT: GRB 161217A: Swift detection of a burst
DATE:    16/12/17 01:54:47 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

V. D'Elia (ASDC), J. A. Kennea (PSU), H. A. Krimm (CRESST/NSF/USRA),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL) and T. Sakamoto (AGU) report on behalf of the
Swift Team:

At 01:27:34 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 161217A (trigger=727167).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is RA, Dec 150.637, +52.389 which is 
   RA(J2000) = 10h 02m 33s
   Dec(J2000) = +52d 23' 21"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a peak starting
around T+35s and lasting about 15 seconds.  (Because this was
an image trigger, the 'trigger time' is not tightly synchronized to
the time of the rate increase.)  The peak count rate
was ~600 counts/sec (15-350 keV), at ~35 sec after the trigger. 

The XRT began observing the field at 01:30:15.5 UT, 160.9 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 150.6517, 52.3592 which
is equivalent to:
   RA(J2000)  = 10h 02m 36.40s
   Dec(J2000) = +52d 21' 33.1"
with an uncertainty of 2.4 arcseconds (radius, 90% containment). This
location is 112 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.  We cannot determine whether the source is
fading at the present time. No spectrum from the promptly downlinked
event data is yet available to determine the column density. 

UVOT took a finding chart exposure of 144 seconds with the White filter
starting 163 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 0.01. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.it). 
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.)