[vsnet-grb-info 14754] Swift trigger 594286: Is likely a noise trigger

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16068
SUBJECT: Swift trigger 594286: Is likely a noise trigger
DATE:    14/04/01 18:52:38 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
V. D'Elia (ASDC), S. T. Holland (STScI), J. A. Kennea (PSU),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU), C. A. Swenson (PSU)
and T. N. Ukwatta (MSU) report on behalf of the Swift Team:

At 18:21:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a possible source coincident with NGC1495 (trigger=594286). 
Swift slewed immediately to the source.  The BAT on-board calculated location is 
RA, Dec 59.640, -44.453, which is 
   RA(J2000)  =  03h 58m 34s
   Dec(J2000) = -44d 27' 10"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is typical for an image trigger, the real-time
TDRSS lightcurve does not show anything. 

The XRT began observing the field at 18:28:34.6 UT, 398.5 seconds after
the BAT trigger. No source was detected in 1.0 ks of promptly
downlinked data, which covered 98% of the BAT error circle. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 401 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
0.01. 

Due to the low significance of this detection (5.92 sigma) the
lack of an XRT or UVOT detection, and the lack of previous activity
from this galaxy, there is a low likelihood that this is a real
astrophysical source.  Further analysis using the full ground-linked data
will be required.