TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4065
SUBJECT: Swift-BAT trigger 158700 is a probable Cosmic Ray Shower Event
DATE:    05/10/07 17:39:48 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott@lheamail.gsfc.nasa.gov>

C. Markwardt (GSFC/UMD), S. Barthelmy (GSFC), S.T. Holland (GSFC/USRA),
J. Kennea (PSU), F. Marshall (GSFC), J. Norris (GSFC), C. Pagani (PSU),
D. Palmer (LANL), M. Perri (ASDC), P. Roming (PSU)
on behalf of the Swift team:

At 17:00:42 UT, Swift-BAT triggered (trigger=158700) on what we tentatively 
believe to be a cosmic ray shower event.  We will not know more until
we get the full data set in about 2-3 hours.

XRT began observing the field at 17:01:40.11 UT (approximately 57 sec
after the BAT trigger) with the XRT in auto state.  The on-board detection
algorithm failed to centroid on a source, so no prompt X-ray position
is available.  The XRT prompt spectrum and lightcurve show no signficant
X-ray emission in the field.  Further analysis will require processing
of the XRT full telemetry data following the next ground station contact.

In the 200 s V-band UVOT image, no new source is detected with respect to
the DSS to a limiting magnitude of 18.5 (5 sigma).