RDC and IMG are greateful to T. Maccacaro for the continuous support and encouragement since the early phases of this work. M. Hattori provided us with unpublished data for AXJ 2019-1127. We thank G. Chincarini, C. Lobo, A. Wolter and G. Zamorani for a careful reading of the paper and useful comments. We thank the Beppo SAX SDC, SOC and OCC teams for the successful operation of the satellite and preliminary data reduction and screening. This research has made use of SAXDAS linearized and cleaned event files produced at the Beppo SAX Science Data Center. IMG acknowledges partial financial support from NSF AST95-00515, from NASA-STScI GO-06668.02-95A and from CNR-ASI grants.
© European Southern Observatory (ESO) 2000
Online publication: December 17, 1999