4 Selection on gamma-ray intensity

A selection in gamma-ray intensity in the BeppoSAX/WFC GRBs could be expected due to the triggering mechanisms of the GRBM. In fact, the GRBM experiment is composed of 4 detectors placed in a box-like configuration, 90$^{\circ}$ one to the other. The trigger condition requires a simultaneous 4 $\sigma$ excess in at least 2 detectors. Events occurring within the WFC field of view are basically on axis for either unit #1 or #3 of the GRBM, and this implies the geometric area of the adjacent detectors to be almost null. Therefore, the onboard trigger relies on scattering effects due to the satellite structures and/or the Earth atmosphere. The typical efficiency for such a scattering is of the order of $10-20\%$.However, the BeppoSAX-SOC has also the ability to recognize events detected by the GRBM but not triggered by the onboard software. The net result is that the peak fluxes of the BeppoSAX GRBs include very weak events, that samples the low-flux tail of the BATSE $\log N-\log S$ distribution. Therefore it appears to be no significant selection on the gamma-ray intensity of the sample of GRBs detected by BeppoSAX/WFC and GRBM.