GCN Circular 6560

B. Sbarufatti (INAF-IASFPA), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), P. J. Brown (PSU),
M. M. Chester (PSU), C. Guidorzi (Univ Bicocca&INAF-OAB),
S. T. Holland (CRESST/GSFC/USRA), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
C. Pagani (PSU), D. M. Palmer (LANL),
P. Romano (Univ. Bicocca & INAF-OAB), M. Stamatikos (NASA/ORAU) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 23:17:39 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070621 (trigger=282808).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 323.804, -24.806 which is 
   RA(J2000)  =  21h 35m 13s
   Dec(J2000) = -24d 48' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with a total duration of at least 40 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~8 sec after the trigger. 

The XRT began observing the field at 23:19:30 UT, 111 seconds after
the BAT trigger. XRT found a bright and fading X-ray source located
at RA, Dec 323.7909, -24.8181 which is
   RA(J2000)  =  21h 35m 09.8s  
   Dec(J2000) = -24d 49' 05.1"
with an uncertainty of 4.7 arcseconds
(radius, 90% containment). This location is 61 arcseconds from the
BAT on-board position, within the BAT error circle. The initial flux
in the 2.5s image was 3.7e-09 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 120 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 3-sigma
upper limit is about 19.2 mag. The upper limit has not been corrected
for the expected Galactic extinction along the line of sight
corresponding to a reddening of E_{B-V} = 0.05 mag.