[vsnet-grb-info 20517] Swift Trigger 823014 is probably not a GRB

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22613
SUBJECT: Swift Trigger 823014 is probably not a GRB
DATE:    18/04/07 04:30:16 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

A. Tohuvavohu (PSU), A. Deich (PSU), C. Gronwall (PSU),
S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC) and D. M. Palmer (LANL)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 04:05:18 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# 823014). 
Also, XRT and UVOT stopped taking data shortly after the trigger 
due to the SAA. The BAT on-board calculated location is 
RA, Dec 209.938, +48.654 which is 
   RA(J2000) = 13h 59m 45s
   Dec(J2000) = +48d 39' 13"
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 04:06:30.5 UT, 72.3 seconds after
the BAT trigger. No source was detected in 160 s of promptly downlinked
data. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

This event was triggered by the BAT rate increase due to the
approach to the SAA, with no peak visible at the time 
of the trigger, and the resulting BAT image peak has only 
marginal significance (6.7 sigma, reduced to 5.1 sigma in 
ground analysis).  In the absence of a confirmation by XRT 
(which had only limited exposure before it stopped taking data due to 
the SAA) we believe that this is probably a statistical fluctuation
in the BAT image, and probably not a GRB.  
However, further observation and analysis of the full dataset,
including post-SAA XRT data starting at t+20 minutes, 
will be required to definitively determine the reality of this event. 

Burst Advocate for this burst is A. Tohuvavohu (aaronb AT swift.psu.edu). 
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.)