EXOSAT X-ray observations of the eclipsing magnetic cataclysmic variable EX Hya.

Abstract

Mechanisms for generating the 67-min rotational X-ray modulation in EX Hya are exmined. It is concluded that the dominant process is probably absorption in material accreting onto the polar regions of the white dwarf which is symmetrically distributed about the rotation axis due to the angular offset of the dipole field. The X-ray emitting region must extend above the white dwarf by more than about one stellar radius in order to explain the gradual ingress and egress of its eclipse by the companion star. Two possible explanations of the partial X-ray eclipse are considered: one in which the companion star occults part of an accretion column above the disk plane and a second where eclipse geometry X-rays are observed form both polar regions of a dipole field but only the emission region below the disk plane is occulted.