GCN Circular 6375

C. Pagani (PSU), M. M. Chester (PSU),
C. Guidorzi (Univ Bicocca&INAF-OAB), S. Immler (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), J. L. Racusin (PSU),
T. Sakamoto (NASA/ORAU), M. Stamatikos (NASA/ORAU) and L. Vetere (PSU)
report on behalf of the Swift Team:

At 05:35:58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070506 (trigger=278693).  Swift slewed to the burst
immediately after the end of the 64 second image trigger. 
The BAT on-board calculated location is RA, Dec 347.217, +10.728 which is 
   RA(J2000) = 23h 08m 52s
   Dec(J2000) = +10d 43' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 6 sec.  The peak count rate
was ~1700 counts/sec (15-350 keV), at ~6 sec after the trigger. 

The XRT began observing the field at 05:38:05 UT, 127 seconds after
the BAT trigger. Using ground-processed quick-look data, XRT found an
uncatalogued X-ray source located at RA, Dec 347.2192, +10.7224 which
is
   RA(J2000) = 23h 08m 52.6s
   Dec(J2000) = 10d 43' 20.7" 
with an uncertainty of 9.0 arcseconds (radius, 90% containment). This
location is 22 arcseconds from the BAT on-board position, within the
BAT error circle. The initial flux in the 2.5s image was 2.5e-10
erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 459 seconds after the BAT trigger. There
is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image
at     
   RA(J2000) =	23h 08m 52.39s (= 347.2183d)   
   DEC(J2000) = +10d 43' 20.3" (= 10.7223d) 
with a 1-sigma error radius of about 0.5 arc sec. This position is 
3.0 arcseconds from the center of the XRT error circle. The estimated 
magnitude is 19.4 with a 1-sigma error of about 0.5 mag. 
No correction has been made for galactic reddening of E(B-V) = 0.040.