GCN Circular 16049

B.-B. Zhang (UAH), S. D. Barthelmy (GSFC), V. D'Elia (ASDC),
J. A. Kennea (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 05:49:48 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 140331A (trigger=594081).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 134.845, +2.707 which is 
   RA(J2000) = 08h 59m 23s
   Dec(J2000) = +02d 42' 25"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual for an image trigger,
there is no obvious variation in the BAT light curve. 

The XRT began observing the field at 05:56:13.2 UT, 385.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 134.8644,
2.7174 which is equivalent to:
   RA(J2000)  = 08h 59m 27.45s
   Dec(J2000) = +02d 43' 02.7"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 79 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. 

The initial flux in the 2.5 s image was 6.70e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 393 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
0.05. 

Burst Advocate for this burst is B.-B. Zhang (bbzhang AT psu.edu). 
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.)