[vsnet-grb-info 18209] GRB 160705B: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19657
SUBJECT: GRB 160705B: Swift detection of a burst
DATE:    16/07/05 21:19:59 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

J. K. Cannizzo (NASA/UMBC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), C. Gronwall (PSU), J. A. Kennea (PSU),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester) and T. N. Ukwatta (LANL) report on behalf of
the Swift Team:

At 21:02:07 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160705B (trigger=703176).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 168.086, +46.721 which is 
   RA(J2000)  =  11h 12m 21s
   Dec(J2000) = +46d 43' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows some weak emission
from T_0 to about T+40 (this is a 64-sec image trigger, and as such
there is seldom anything see in the raw real-time TDRSS telemetry). 
The duration of about 40 sec.  The peak count rate
was ~600 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 21:04:27.7 UT, 140.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 168.10943,
46.70085 which is equivalent to:
   RA(J2000)  = 11h 12m 26.26s
   Dec(J2000) = +46d 42' 03.1"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 92 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 (1.19 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.7
(+2.18/-1.93) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 9.31e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 148 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
0.01. 

Burst Advocate for this burst is J. K. Cannizzo (cannizzo AT milkyway.gsfc.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.)