The X-ray emission of Intermediate Polars: the BeppoSAX view and the role of current missions

Abstract

Intermediate Polars (IPs) are the most intriguing systems among Cataclysmic Variables (CVs), as the X-ray spectral and temporal behaviour is not similar in all members. The simultaneous study of broad–band X-ray temporal and spectral properties is crucial to characterize the accretion geometry and the physical conditions of the accretion flow onto moderately (B<10-20 MG) magnetized white dwarfs. Thanks to the wide energy coverage, BeppoSAX observations of bright IPs have allowed to infer the accretion mode, the presence of complex patchy absorption in the pre–shock flow and of a Compton reflection component from the white dwarf surface as well as to measure simultaneously the temperature of the post–shock region and that of the irradiated poles of the white dwarf atmosphere. The observations show that accretion in these systems cannot be reconciled with a single scenario, accounting for their soft and hard X-ray behaviour. Many known systems and IP candidates still lack of X-ray characterization in both soft and hard bands, for which current X–ray missions are providing new and unprecedented results.