TITLE:   GCN CIRCULAR
NUMBER:  33053
SUBJECT: Swift Trigger 1144538 is not a GRB
DATE:    22/12/15 04:01:42 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

S. Dichiara (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII),
D. M. Palmer (LANL), M. H. Siegel (PSU), A. Tohuvavohu (U Toronto) and
M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 03:35:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a marginal image peak (trigger=1144538).  Swift slewed immediately
to the peak location.  The BAT on-board calculated location is 
RA, Dec 54.789, -27.433 which is 
   RA(J2000) = 03h 39m 09s
   Dec(J2000) = -27d 25' 57"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows the count rate starting
to rise as Swift approaches the South Atlantic Anomaly (SAA) but
does not show a typical GRB peak. 

The XRT position notice sent was due to XRT centroiding on a likely cosmic
ray strike. There is no clear detection of an X-ray afterglow. 

Due to the rate trigger occurring during the approach to the SAA, the lack of
a strong peak in the BAT light curve, the marginal significance (6.55 sigma)
of the BAT image peak, and the lack of an XRT afterglow source, we
believe that this event is a statistical fluctuation and not an astrophysical
event.  A final determination of the nature of this trigger will require
the full ground-linked dataset.