mechanisms). Thus we predict that for most short bursts there will be a gap between the burst and the beginning of the afterglow. We have already remarked that at this stage one cannot tell whether the remaining 30% smooth short bursts are produced by external or by internal shocks. This could be tested in the distant future with better data. However, there are clear predictions concerning the afterglow that could distinguish between the two possibilities. If these short GRBs are produced by internal shocks then we expect a clear gap between the end of the GRB and the onset of the x-ray afterglow. If on the other hand these short bursts are produced by external shocks then we predict that the afterglow would continue immediately with no interpretation after the GRB and its features would be a direct extrapolation of the properties of the GRB.

Appendix -The algorithm {#appendix--the-algorithm .unnumbered}
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Our algorithm finds the peaks of the bursts. Each peak corresponds to a single pulse; a pulse is the basic event of the light curve. The algorithm is based on the algorithm suggested by Li & Fenimore (1996). Li & Fenimore define a time bin $ t_{p} $ (with 