[vsnet-grb-info 23976] Swift Trigger 931484 is not a GRB

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26075
SUBJECT: Swift Trigger 931484 is not a GRB
DATE:    19/10/25 18:32:43 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

A. P. Beardmore (U Leicester), A. A. Breeveld (UCL-MSSL),
J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (PSU) and
A. Tohuvavohu (Toronto) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 18:16:12 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a low significance image peak (trigger=931484). 
Swift slewed immediately to the location. 
The BAT on-board calculated location is 
RA, Dec 139.771, +1.384 which is 
   RA(J2000) = 09h 19m 05s
   Dec(J2000) = +01d 23' 02"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve does not show
any significant structure. 

The XRT began observing the field at 18:17:21.8 UT, 68.9 seconds after
the BAT trigger. No source was detected in 461 s 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 73 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. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
BAT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.03. 

Based on the low significance of the event in the image (6.56 sigma), 
the lack of obvious activity in the BAT lightcurve, 
and the non-detection by XRT we believe that this is 
probably a noise fluctuation in the image and not an astrophysical event.