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4 Noise evaluation

If the GRBs are located at a cosmological distance, the associated GW signal has to be very small. Because of this, in the next step of the analysis we have selected only those events that have an energy of $\le 200$ mK. So a list of 87177 GW candidate events with average energy of 100 mK has been obtained, distributed over 652 non continuous days, with a mean rate of $\sim 133$ events per day. The time distribution of these events relative to the trigger time of each GRB in a window of $\pm 300$ s is shown in Fig. 1.

  
\begin{figure}

\includegraphics [width=7cm,clip]{R3f1.eps}\end{figure} Figure 1: Number of events with energy $\sim 100$ mK with respect to the GRB trigger time

The total number of 393 GW candidate events found in the $\pm 300$ s window, over the 441 GRBs analysed, indicates that the average density of the GW events

around the trigger time, 128 events per day, is compatible with the mean rate of $\sim 133$ over the entire period. Further we notice that in the chosen window there are not significant coincidence excesses either at the trigger time or at different instants.


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