This research has made use of the NASA/IPAC extragalactic database (NED) which is operated by the Jet Propulsion Laboratory, Caltech, under contract with the National Aeronautics and Space Administration. We have also used the public radio data of the Green Bank Interferometer. We thank the italian space agency ASI for financial support and the Beppo SAX space data center for constant help. Annalisa Celotti and Giovanni Fossati acknowledge the Italian MURST for financial support.
© European Southern Observatory (ESO) 1999
Online publication: July 16, 1999