TITLE:   GCN CIRCULAR
NUMBER:  6380
SUBJECT: GRB 070507: Swift detection of a possible cosmic ray shower event or a possible burst
DATE:    07/05/07 13:49:10 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

L. Vetere (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
M. M. Chester (PSU), C. Guidorzi (Univ Bicocca&INAF-OAB),
S. T. Holland (CRESST/GSFC/USRA), S. Immler (GSFC/USRA),
J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
V. Mangano (INAF-IASFPA), 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), J. L. Racusin (PSU),
P. Romano (Univ. Bicocca & INAF-OAB), T. Sakamoto (NASA/ORAU),
B. Sbarufatti (INAF-IASFPA) and M. Stamatikos (NASA/ORAU) report on
behalf of the Swift Team:

At 13:24:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located possbile GRB 070507 (trigger=278809).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 243.010, +59.488 which is 
   RA(J2000) = 16h 12m 02s
   Dec(J2000) = +59d 29' 16"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single very
short peak in the highest energy band only, which is consistent with 
this event being due to a cosmic ray shower.  The peak count rate
was ~1000 counts/sec (15-350 keV), at 0 sec after the trigger.  We
will be able to conclusively determine the nature of the event after
receipt of the full event data in approximately one hour. 

The XRT began taking data at 13:29:14 UT, 263 seconds after the BAT
trigger.  The XRT on-board centroid algorithm did not find a source in the
image and no prompt position is available.  We are waiting for down-linked
data to detect and determine a position for the source. 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 268 seconds after the BAT trigger. No afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT 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
BAT 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 0.02.