[vsnet-grb-info 15171] Swift Trigger 602668 is probably not an astrophysical source

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16463
SUBJECT: Swift Trigger 602668 is probably not an astrophysical source
DATE:    14/06/26 15:54:51 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

M. G. Bernardini (INAF-OAB), J. R. Cummings (NASA/UMBC),
P. D'Avanzo (INAF-OAB), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU),
A. Melandri (INAF-OAB), K. L. Page (U Leicester), M. H. Siegel (PSU)
and E. Sonbas (NASA/GSFC/Adiyaman Univ.) report on behalf of the Swift
Team:

At 15:27:39 UT, the Swift Burst Alert Telescope (BAT) found a marginal-
significance image peak with a location near to the galaxy 
NGC4215 (trigger=602668).  Swift slewed immediately to the location. 
The BAT on-board calculated location is 
RA, Dec 183.900, +6.468 which is 
   RA(J2000) = 12h 15m 36s
   Dec(J2000) = +06d 28' 04"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  No BAT lightcurve data is immediately available,
but the image was generated by schedule, and not as a result
of a rate trigger. 

The XRT began observing the field at 15:40:01.0 UT, 741.3 seconds after
the BAT trigger. No source was detected in 589 s of promptly downlinked
data, which covered 91% of the BAT error circle. 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 744 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
0.02. 

Due to the low significance of the peak (6.06 sigma), the lack of
a corresponding rate trigger on this 8-minute untriggered image,
the 6 arcminute offset of the peak from the galaxy, and
the lack of confirmation by the XRT and UVOT, we believe that
this event is a noise fluctuation in the image.  Confirmation
will require the full downlinked dataset.