GCN Circular 6542

R. L. C. Starling (U Leicester), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
C. Guidorzi (Univ Bicocca&INAF-OAB), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC),
G. Sato (GSFC/ISAS), M. Stamatikos (NASA/ORAU),
D. E. Vanden Berk (PSU) and L. Vetere (PSU) report on behalf of the
Swift Team:

At 16:29:33 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070616 (trigger=282445).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 32.155, +56.948 which is 
   RA(J2000)  =  02h 08m 37s
   Dec(J2000) = +56d 56' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows nothing much 
around T_zero (as is typical for image triggers).  We note that there
is bright and variable activity in the TDRSS lightcurve starting at T+100 sec
and lasting to 600 sec.  This may be long-term burst activity, although we can
not rule out a contribution from a bright galactic source such as Cyg X-1
coming into the FOV (due to the slew).  We will be able to separate this 
ambiguity when we get the full Malindi data to construct a mask-weighted 
lightcurve. 

The XRT began observing the field at 16:31:44 UT, 131 seconds after the
BAT trigger. XRT found a bright, variable and fading, uncatalogued X-ray source. 
Using prompt downlinked data we find a position of 
located at RA, Dec 32.1513, +56.9451 which is
   RA(J2000)  =  02h 08m 36.3s
   Dec(J2000) =  56d 56' 42.5"
with an uncertainty of 4.9 arcseconds (radius, 90% containment). 
This location is 12.7 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 7.6e-09 erg/cm2/s (0.2-10 keV). 
We note that this is 3.1 arcseconds from source USNO-B1.0 1469-0076513. 


UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 142 seconds after the BAT trigger. No 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 18.5 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 large, but uncertain extinction expected.