Neutron-Star Accretion in a Stellar Wind: Model for a Pulsed X-Ray Source

Many of the characteristics of the pulsing X-ray sources Cen X-3 and Her X-1 are explicable in terms of a simple model. A rotating magnetized neutron star orbits a more massive slightly evolved star and accretes mass from the stellar wind emanating from that star. An analysis of the tidal disruption problem shows that the period, velocity amplitude, and eclipse duration of the X-ray source permit the neutron star to have a mass of 1 M0, determine the inclinations to be , and require separations, masses, radii, and spectral types of the companion stars to be approximately (18 R0, 8 R0), (20 M0, 2 M0), (12 R0, 4 R0), and (B2 III, F5 III), for Cen X-3 and Her X-1, respectively. Accretion rate is restricted to less than l0- M0 per year in any case, by the Eddington limit, and calculated to be l0- M0 per year three orders of magnitude less than the moderate stellar winds required. Infalling gas interacting with the neutron star magnetosphere causes its rotation period to approach an equilibrium value which is on the order of seconds if the surface field is 10' gauss. The X-ray spectrum coming from well-defined areas near each magnetic pole is also fixed by system parameters. The theory applied to Cen X-3 is consistent with a surface field of 10' gauss and X-ray luminosity of 1036.5 ergs 1 Subject headings: binaries - magnetic stars - neutron stars - X-ray sources