[vsnet-grb-info 10885] Swift-BAT Trigger 501485 is noise

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12305
SUBJECT: Swift-BAT Trigger 501485 is noise
DATE:    11/08/26 09:06:44 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

B.-B. Zhang (PSU), S. D. Barthelmy (GSFC), V. D'Elia (ASDC),
C. Gronwall (PSU), P. T. O'Brien (U Leicester),
J. P. Osborne (U Leicester) and D. M. Palmer (LANL) report on behalf
of the Swift Team:

At 08:30:08 UT, the Swift Burst Alert Telescope (BAT) triggered on noise 
(trigger=501485).  Swift slewed immediately. 
The BAT on-board calculated location is 
RA, Dec 264.165, -27.375, which is 
   RA(J2000)  =  17h 36m 40s
   Dec(J2000) = -27d 22' 29"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows nothing significant
as is typical for an image trigger. 

The XRT began observing the field at 08:32:04.8 UT, 116.1 seconds after
the BAT trigger. No source was detected in 1.2 ks of promptly
downlinked data. We are waiting for the full dataset to detect and
localise the XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 119 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT error circle. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. The 8'x8' region for the list of sources generated on-board covers
100% of the BAT error circle. Because of the density of catalogued stars,
further analysis is required to report an upper limit for any afterglow in the
region. No correction has been made for the large, but uncertain extinction
expected. 

Due to the marginal significance of the detection, the lack of an XRT
source, the poor positional match with any known gamma-ray source,
and the increase in the noise level caused by Sco X-1 and other
galactic center sources in the Field of View, we believe that this
trigger was probably a noise fluctuation. 

Burst Advocate for this burst is B.-B. Zhang (bbzhang AT 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.)