The BeppoSAX satellite is a joint Italian-Dutch program. The authors wish to thank T.Mineo and A.Orr for useful discussions and M.Salvati and G.Stirpe for comments on the manuscript. The anonymous referee's comments helped us to better focus several issues. MG acknowledges the receipt of an ESA Research Fellowship. Financial support from ASI and CNR is acknowledged. This research has made use of data obtained through the High Energy Astrophysics Science Archive Research Center Online Service, provided by the NASA/Goddard Space Flight Center and of the NASA/IPAC Extragalactic Database, which is operated by the Jet Propulsion Laboratory Caltech, under contract with NASA.
© European Southern Observatory (ESO) 1999
Online publication: May 21, 1999