[vsnet-grb-info 20467] Swift Trigger 819863 is not a GRB

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22563
SUBJECT: Swift Trigger 819863 is not a GRB
DATE:    18/03/30 03:23:32 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

A. Deich (PSU), H. A. Krimm (NSF/USRA), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL) and A. Tohuvavohu (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 03:09:02 UT, the Swift Burst Alert Telescope (BAT) triggered during
the count rate increase during the approach to the SAA, and found
a low-significance peak in the resulting image (trigger=819863).  
Swift slewed immediately to the location. 
The BAT on-board calculated location is 
RA, Dec 95.803, -64.954 which is 
   RA(J2000) = 06h 23m 13s
   Dec(J2000) = -64d 57' 12"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a continuous
increase as expected on entering the SAA. 

The XRT began observing the field at 03:10:27.2 UT, 85.1 seconds after
the BAT trigger. However, the source automatically identified on-board
was a cosmic ray, caused by the proximity of Swift to the SAA. 

Due to the low significance of the image (6.55 sigma), the lack
of a GRB-like peak during the increasing particle background, and
the non-detection of an afterglow by XRT, we believe that
this is not a GRB.