GCN Circular 19171

A. D'Ai (INAF-IASFPA), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
A. Y. Lien (GSFC/UMBC), A. Maselli (INAF-IASFPA),
L. M. McCauley (PSU), D. M. Palmer (LANL),
B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU) and
T. N. Ukwatta (LANL) report on behalf of the Swift Team:

At 02:37:15 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160313A (trigger=678929).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 183.788, +57.293 which is 
   RA(J2000)  =  12h 15m 09s
   Dec(J2000) = +57d 17' 34"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several peaks
with a total duration of about 40 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~30 sec after the trigger. 

The XRT began observing the field at 02:39:48.3 UT, 152.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 183.7969, 57.2840 which
is equivalent to:
   RA(J2000)  = 12h 15m 11.24s
   Dec(J2000) = +57d 17' 02.3"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 36 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. No
spectrum from the promptly downlinked event data is yet available to
determine the column density. 

UVOT took a finding chart exposure of 150 seconds with the White
filter  starting 198 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 A. D'Ai (antonino.dai 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.)