Coincidence analysis between periodic source candidates in C6 and C7 Virgo data

In this paper, we describe the analysis performed in the data of C6 and C7 commissioning runs of Virgo for the search of periodic sources of gravitational waves. The analysis is all-sky, covers the frequency range between 50 Hz and 1050 Hz and neutron star spin-down rate below 1.58 x 10-8 Hz s-1. Coincidences in the source parameter space between candidates found in the two data sets are required to reduce the false alarm probability. The procedure used to estimate the detection efficiency of the analysis pipeline, through the injection of simulated signals in the data, is also described