Astron. Astrophys. 353, 440-446 (2000)

Acknowledgements

We wish to thank the BeppoSAX Scientific Data Center for assistance and the HELLAS group for the useful and stimulating collaboration. We would also like to thank F.Fiore, P.Giommi, A.Comastri, S.Molendi and A.Vecchi for supplying us the data involved in this work and for several useful discussions, R.Gilli, G.Risaliti and M.Salvati for valuable comments on the manuscript and the referee Dr.W.Brinkmann for suggestions to improve the final version. This work was partially supported by the Italian Space Agency, and by the Ministry for University and Research (MURST) under grant COFIN 98-02-3

© European Southern Observatory (ESO) 2000

Online publication: December 17, 1999
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