TITLE:   GCN CIRCULAR
NUMBER:  23585
SUBJECT: Swift Trigger 880127 is not a GRB
DATE:    18/12/29 00:12:51 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>

S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC),
J. A. Kennea (PSU), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC),
M. J. Moss (George Washington University), M. H. Siegel (PSU),
A. Tohuvavohu (PSU) and T. N. Ukwatta (LANL) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 23:50:28 UT, the Swift Burst Alert Telescope (BAT) triggered on a noise
fluctuation while entering the SAA.  Swift slewed immediately to the location. 
The BAT on-board calculated location is 
RA, Dec 18.159, -60.951, which is 
   RA(J2000)  =  01h 12m 38s
   Dec(J2000) = -60d 57' 03"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a sharply rising background
while entering the SAA.  This is not a GRB or anything astrophysical. 

The XRT began observing the field at 23:52:24.9 UT, 116.5 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

Due to the lack of a clear peak in the BAT lightcurve, the
marginal (6.61 sigma) BAT image peak, and the lack of an
XRT counterpart, we believe that this event was due to particle
background near the SAA and is not an astrophysical event.