GCN Circular 23331

P. D'Avanzo (INAF-OAB), D. N. Burrows (PSU), J. A. Kennea (PSU),
D. M. Palmer (LANL), B. Sbarufatti (PSU), M. H. Siegel (PSU) and
A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 19:06:28 UT, the Swift Burst Alert Telescope (BAT) triggered
due to rising rates during the approach to the SAA and found a
low-significance peak in the resulting image (trigger=866757).  
Swift did not slew to the location due to a Moon constraint. 
The BAT on-board calculated location is 
RA, Dec 264.743, -12.473 which is 
   RA(J2000) = 17h 38m 58s
   Dec(J2000) = -12d 28' 22"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows the pre-SAA
rise in count rates but does not show a peak around T=0. 

Due to a Moon observing constraint, Swift cannot slew to the BAT
position until 02:59 UT on 2018 October 16. No XRT
or UVOT follow-ups are planned. 

Due to the low significance of the on-board peak detection
(6.5 sigma, falling to 6.2 sigma in ground analysis), 
the lack of a visible peak in the BAT lightcurve,
and the fact that Swift was approaching the SAA at the time,
we believe that this is most likely a chance fluctuation in
the image plane and not a GRB.  Further analysis of the full
downlinked dataset will be needed to determine the reality
of this event. 

Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo AT brera.inaf.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.)