TITLE:   GCN CIRCULAR
NUMBER:  14767
SUBJECT: Swift Trigger 557466 is probably not real. 
DATE:    13/06/05 09:23:11 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani@dark-cosmology.dk>

M. Stamatikos (OSU/NASA/GSFC), M. M. Chester (PSU),
S. T. Holland (STScI), D. Malesani (DARK/NBI), A. Melandri (INAF-OAB),
T. Sakamoto (AGU), R. L. C. Starling (U Leicester) and
E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift Team:

At 08:47:33 UT, the Swift Burst Alert Telescope (BAT) triggered and
located trigger 557466.  Swift slewed immediately to the trigger location. 
The BAT on-board calculated location is 
RA, Dec 53.405, -31.355 which is 
   RA(J2000) = 03h 33m 37s
   Dec(J2000) = -31d 21' 16"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual with an image trigger, the 
currently available BAT light curve does not show much structure.  This
trigger was a sub threshold trigger (6.1 sigma significance), and is 
spatially coincident with a nearby galaxy (10.2 arc minutes from NGC 1366). 
Further analysis of data on the ground will be required to verify the 
reality of this event. 

The XRT began observing the field at 08:49:37.2 UT, 123.9 seconds after
the BAT trigger. No source was detected in 987 s of promptly downlinked
data, which covered 90% 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 128 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. 

Given the low significance and the lack of an XRT counterpart, we cannot assess
whether this trigger is real. We are waiting for the download of the full
dataset to undertake further analysis. 

Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 AT nasa.gov). 
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.)