X-Ray Timing and Spectral Measurements of X Persei

Abstract

The results of an X-ray timing and spectral study of the Be star X-ray binary system X Per are reported, based on two series of Exosat observations. The timing measurements indicate that the neutron star in the X Per system was in a net spin-down mode during the 1984-1986 period and that this trend may have been in progress since 1978. The phase-averaged X-ray spectrum is consistent with a power law of photon spectral index 1.2 with a high-energy cutoff which becomes pronounced above 5 keV. The spectral form remains fairly constant with pulse phase, except for a brief episode of spectral hardening near pulse minimum. The results are discussed in terms of current models for wide-orbit binaries containing a Be star primary and an accreting neutron star.