TITLE:   GCN CIRCULAR
NUMBER:  20718
SUBJECT: Swift Trigger 739517 is probably not a GRB
DATE:    17/02/22 03:10:01 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

V. D'Elia (ASDC), A. Cholden-Brown (PSU), A. D'Ai (INAF-IASFPA),
A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL), T. Sakamoto (AGU) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 02:24:31 UT, the Swift Burst Alert Telescope (BAT) triggered 
on increasing count rate due to the approach to the SAA and
produced an image with a marginal-significance peak (trigger=739517). 
Swift slewed to the location after a brief delay due to an observing 
constraint.  The BAT on-board calculated location is 
RA, Dec 230.670, -55.739 which is 
   RA(J2000) = 15h 22m 41s
   Dec(J2000) = -55d 44' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows the increasing
count rate due to approaching the SAA, but no obvious peak at the
trigger time. 

The XRT began observing the field at 02:39:06 UT, 875 seconds after
the BAT trigger. No source was detected in 639 s of promptly downlinked
data. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 1464 seconds after the BAT trigger, once Swift had left the SAA. 
No credible afterglow candidate has been found in the initial data products. 

Due to the lack of a clear peak in the BAT lightcurve, the
marginal (6.5 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. 

Further analysis will require the full downlinked dataset. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.it). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)