  A search for gravitational wave burst events has been performed with the
Virgo C7 commissioning run data that have been acquired in September 2005 over
five days. It focused on un-modeled short duration signals in the frequency
range 150 Hz to 2 kHz. A search aimed at detecting the GW emission from the
merger and ringdown phases of binary black hole coalescences was also carried
out. An extensive understanding of the data was required to be able to handle a
burst search using the output of only one detector. A 90% confidence level
upper limit on the number of expected events given the Virgo C7 sensitivity
curve has been derived as a function of the signal strength, for un-modeled
gravitational wave search. The sensitivity of the analysis presented is, in
terms of the root sum square strain amplitude, $h_{rss} \simeq 10^{-20} /
\sqrt{Hz}$. This can be interpreted in terms of a frequentist upper limit on
the rate ${\cal{R}}_{90%}$ of detectable gravitational wave bursts at the level
of 1.1 events per day at 90% confidence level. From the binary black hole
search, we obtained the distance reach at 50% and 90% efficiency as a function
of the total mass of the final black hole. The maximal detection distance for
non-spinning high and equal mass black hole binary system obtained by this
analysis in C7 data is $\simeq$ 2.9 $\pm$ 0.1 Mpc for a detection efficiency of
50% for a binary of total mass $80 M_{\odot}$.
