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T. Di Salvo, N. R. Robba, R. Iaria (Dipartimento di Scienze Fisiche ed Astronomiche di Palermo), L. Stella, L. Burderi (Osservatorio Astronomico di Monteporzio - Roma)
Recently the broad band capabilities of BeppoSAX have detected the presence of hard excess, above 20 keV, in Low Mass X-ray Binaries of the Z class, that can be fit to power laws. These components are variable and their presence is probably connected to the state of the source. In particular, for every source in which this component has been observed, its intensity seems to be larger at lower accretion rates and seems to decrease at higher accretion rates. Here we review these observations and discuss about the possible origin of these hard tails.