7 Open questions and possible improvements

We can therefore state that BeppoSAX has discovered a phenomenology that is not common to all sources but shows at least less variance than the major features of GRBs in the classical band. Most GRBs have associated an afterglow source with a hard, non thermal, spectrum, and low absorption and most of them fade according to a smooth power law. How much this sample is representative of all GRBs depends how much we are conditioned from selection effects and this study is still in a very preliminary stage (Feroci et al. 1999). Some features common to most of the objects, such as the association with a host (4 with a measured high red-shift) fix the distance scale for a large subset. This is a dramatic improvement of the scenario. But still we doubt that other important features may escape us due to instrumental limits and other selection effects.

• 1) Do Gamma-Ray Burst without afterglow sources exist?
• 2) Are some Gamma-Ray Burst associated with SN?
• 3) Are short bursts generating afterglows as the long ones?
• 4) Do Gamma-Ray Burst without Gamma-Rays exist?

Question 1) will not be answered by SAX that cannot distinguish between fast afterglow and no afterglow. Question 2) requires more GRBs from BeppoSAX and a more careful search for afterglows. Question 3) should in principle be answered by BeppoSAX. As shown before all GRBs detected in the WFCs have a long duration. A lower sensitivity to short bursts may be due to the present trigger criteria of GRBM (a short integration time of 1 s). But we have a rich sample of short bursts detected with GRBM and, in any case, we recall that the BATSE triggers and positions are systematically monitored: no short burst has apparently occurred, so far, in the field of view of a WFC. In another paper (Smith et al. 1999) we describe the efforts to improve the detection of short bursts at quick look level. The actions to answer question 4) (GRBs with a low Gamma-Ray content and no Gamma-Ray trigger) are already operative. Due to the improved skill and procedures at the Science Operation Center, ad after the detection of GRB 980613, we expect some results in this direction.