[vsnet-grb-info 17816] GRB 160408A: Swift detection of a short burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19260
SUBJECT: GRB 160408A: Swift detection of a short burst
DATE:    16/04/08 06:39:08 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

P.A. Evans (U Leicester), S. D. Barthelmy (GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Swift Team:

At 06:25:43 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160408A (trigger=682059).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 122.557, +71.140, which is 
   RA(J2000)  =  08h 10m 14s
   Dec(J2000) = +71d 08' 25"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single spike
with a duration of about 0.5 sec.  The peak count rate
was ~5000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 06:27:18.5 UT, 94.8 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 122.6235, 71.1284 which
is equivalent to:
   RA(J2000)  = 08h 10m 29.64s
   Dec(J2000) = +71d 07' 42.3"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 87 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 (4.18 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.9
(+3.04/-2.61) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 98 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 0.03. 

Burst Advocate for this burst is P.A. Evans (pae9 AT star.le.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.)