2 New instrumentation to solve old problems

To achieve the goal of a simultaneous detection of an optical-$\gamma$-ray event the optical telescope must be already observing that field from where the GRB will be received. To do this the minimal requisite is a wide field optical telescope scanning the sky area under observation by $\gamma$-ray satellite. As an example we now analyze the following configuration: i) telescope: mirror diameter D=1 m, focal ratio f = 1:1, size of field $l=3^{\circ}$, scale factor $fs=206\hbox{$^{\prime\prime}$}$ mm^-1; ii) detector: two $2\times 2$ CCD arrays, each CCD featuring $25\times25$ mm active area, 40000 rebinned pixels (with pixel size $d=300~\mu$m, corresponding to about $70\hbox{$^{\prime\prime}$}$ in the focal plane), quantum efficiency $\eta=40\%-80\%$ in the range $4000-8000~{\mbox \AA}$, read-out time 1 s (equal to the exposure time, to allow double buffer image acquisition by switching between the two arrays).

We now evaluate the detection limit and the catching probability when such a telescope is scanning the $\gamma$ detector field of view. We assume 1 s exposures and a 0.1-0.5 s shifting time from one position to the next.