1 Introduction

There are at least two possibilities to obtain information on the behaviour of X-ray, optical and radio transients connected with GRBs during or after the $\gamma$ event. The first way is the continuous monitoring of the sky region coinciding with the field of view of the $\gamma$-ray detectors. In this case we must use telescopes with maximum field of view, equipped with high temporal resolution panoramic detectors.

Another opportunity is offered by cosmological GRBs in the case of repetition of the event, if a repetition of the event occurs, as a result of gravitational lensing produced by an interposed galaxy. The shape of the repeated light curves is identical to the original one, taking into account the galaxy absorption effects. By summing the information obtained in all the wavelength ranges during one or two repetitions it might be possible to reconstruct the behavior of the variable source during, after and also before the $\gamma$ burst. The main difficulty is to predict the time of the first repetition with good accuracy (the delay is caused by several parameters; most of them are unknown, such as redshifts of the GRB source and of the lens galaxy, characteristics of the lens galaxy structure and so on). For this reason, in order to detect the first repetition we need to monitor the transient throughout long periods of time. If a repetition is registered, we can estimate some parameters and predict the time of the second repetition with good enough accuracy. We already discussed this problem with respect to GRB 970508 (Beskin et al. 1998a); now, a wider sample of galaxies and GRBs configuration is analyzed.