[vsnet-grb-info 2252] Swift-BAT Trigger 159578 is a possible burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4091
SUBJECT: Swift-BAT Trigger 159578 is a possible burst
DATE:    05/10/13 17:21:50 GMT
FROM:    Hans Krimm at NASA-GSFC  <krimm at milkyway.gsfc.nasa.gov>

J. Cummings (GSFC-NRC), A. Beardmore (U. Leicester), N. Gehrels (GSFC),
O. Godet (U. Leicester), C. Gronwall (PSU), J. Kennea (PSU),
H. Krimm (GSFC-USRA), F. Marshall (GSFC), K. Page  (U. Leicester),
D. Palmer (LANL), on behalf of the Swift team:

At 16:50:26.71 UT, Swift-BAT triggered and located a possible
point source (trigger=159578).  The BAT on-board calculated
location is RA,Dec 247.515d, -4.399d {+16h 30m 04s, -04d 23' 54"}
(J2000), with an uncertainty of 3 arcmin (radius, 90% containment,
stat+sys). This is a very marginal detection and only further
analysis of the full data set in a few hours will allow us to determine if
this is a genuine burst or just a chance fluctuation.

Swift slewed immediately to the burst and XRT began observing at
16:51:35 UT, 68 seconds after the BAT trigger. XRT was unable to
centroid on any source. We await ground analysis of the early XRT data
following the first Malindi pass.   The trigger was in the SAA, which
produces a high count rate in the XRT, thus making identification of
a point source difficult.

There are no UVOT TDRSS data at this time because the trigger
occurred in the SAA.

Two reasons why this identification is marginal are
(1) the BAT image significance is very low (6.36 sigma), (2) the
trigger happened on the rising edge of Swift's entry into the SAA,
Since the light curve is dominated by the rising background it is impossible
at this point to tell anything about the trigger profile at this time.