[vsnet-grb-info 27117] Swift Trigger 1015615 is not a GRB

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29220
SUBJECT: Swift Trigger 1015615 is not a GRB
DATE:    21/01/02 00:33:05 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

S. D. Barthelmy (GSFC), M. G. Bernardini (INAF-OAB),
P. D'Avanzo (INAF-OAB), C. Gronwall (PSU), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. J. Klingler (PSU), N. P. M. Kuin (UCL-MSSL),
S. Laha (GSFC/UMBC/CRESST), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB),
D. M. Palmer (LANL) and T. Sbarrato (INAF-OAB) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 00:17:12 UT, the Swift Burst Alert Telescope (BAT) triggered on
background noise during high background increase while entering 
the SAA (trigger=1015615). The BAT light curve shows the background 
increase near the SAA, without any significant burst structure. 

The XRT began observing the field at 00:18:47.7 UT, 95.1 seconds after
the BAT trigger. No valid point source was found in the XRT data. Automated
position reported through GCN Notices is due to a cosmic ray, and should 
be ignored. 

This event was initiated by the BAT rate increase on approach to 
the SAA, which yielded an image with a marginal (6.5 sigma) fluctuation. 
Based on the lack of a GRB-like rate increase above the ramping up
BAT rates on SAA approach, the low significance of the image peak, 
and the non-detection of an XRT afterglow, we believe that this is
not an astrophysical event.