[vsnet-grb-info 18464] GRB 160912A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19912
SUBJECT: GRB 160912A: Swift detection of a burst
DATE:    16/09/12 16:39:36 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

J. K. Cannizzo (NASA/UMBC), S. D. Barthelmy (GSFC),
A. A. Breeveld (UCL-MSSL), D. N. Burrows (PSU), A. D'Ai (INAF-IASFPA),
V. D'Elia (ASDC), S. W. K Emery (UCL-MSSL), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC),
B. Mingo (U Leicester), K. L. Page (U Leicester) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 16:07:43 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160912A (trigger=711914).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 301.518, +57.543, which is 
   RA(J2000)  =  20h 06m 04s
   Dec(J2000) = +57d 32' 36"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is typical for image triggers, the BAT light curve
does not show anything significant over the trigger window.  However, at ~T+150 sec
there is a flare in the light curve (~1300 cnts/sec). 

The XRT began observing the field at 16:09:57.0 UT, 134.0 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 301.4981,
57.5655 which is equivalent to:
   RA(J2000)  = 20h 05m 59.56s
   Dec(J2000) = +57d 33' 55.8"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 89 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 note the presence in the XRT raw light curve of a large X-ray flare 
coincident with the BAT flare mentioned above. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 2.35
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 137 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
0.20. 

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.)