[vsnet-grb-info 20830] Trigger 846740: Swift trigger near NGC5055

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22928
SUBJECT: Trigger 846740: Swift trigger near NGC5055
DATE:    18/07/08 13:55:21 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), V. D'Elia (ASDC),
S. W. K Emery (UCL-MSSL), J.D. Gropp (PSU), N. P. M. Kuin (UCL-MSSL),
S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC) and A. Tohuvavohu (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 13:33:38 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a low significance source (trigger=846740).  Swift slewed immediately
to the location.  The BAT on-board calculated location is 
RA, Dec 198.919, +41.897, which is 
   RA(J2000)  =  13h 15m 41s
   Dec(J2000) = +41d 53' 50"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is typical for image triggers, the real time
light curve does not show anything significant.  Further, this trigger is
very weak with a 5.93 sigma in the image domain.  This low-significance trigger
was due to being near NGC5055. 

The XRT began observing the field at 13:36:28.0 UT, 169.3 seconds after
the BAT trigger. No source was detected in 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 173 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. 

Given the low significance in BAT and the lack of a detection in XRT, we believe
this to be a noise fluctuation trigger near a known galaxy (NGC5055).  Further
analysis will be done when the full data set is downloaded.