[vsnet-grb-info 11147] GRB 111117A: Swift detection of a short hard burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12559
SUBJECT: GRB 111117A: Swift detection of a short hard burst
DATE:    11/11/17 12:27:17 GMT
FROM:    David Burrows at PSU/Swift  <burrows at astro.psu.edu>

V. Mangano (INAF-IASFPA), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
S. Campana (INAF-OAB), J. R. Cummings (NASA/UMBC), V. D'Elia (ASDC),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),
O. M. Littlejohns (U Leicester), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), S. R. Oates (UCL-MSSL),
C. Pagani (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), E. Sonbas (GSFC/USRA/Adiyaman Univ.),
R. L. C. Starling (U Leicester), C. A. Swenson (PSU) and
E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team:

At 12:13:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 111117A (trigger=507901).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 12.702, +23.021 which is 
   RA(J2000) = 00h 50m 49s
   Dec(J2000) = +23d 01' 16"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 0.6 sec.  The peak count rate
was ~6140 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 12:14:58.7 UT, 76.8 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 12.6925, 23.0103 which
is equivalent to:
   RA(J2000)  = 00h 50m 46.19s
   Dec(J2000) = +23d 00' 36.9"
with an uncertainty of 2.6 arcseconds (radius, 90% containment). This
location is 50 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.70 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 3
(+2.73/-2.30) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
136 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 19.2 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 18.0 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.03. 

Burst Advocate for this burst is V. Mangano (vanessa AT ifc.inaf.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.)