The origin of long-period X-ray pulsars

Abstract

Several relatively bright, persistent X-ray sources display regular pulses, with periods in the range of (0.7–10) × 103 s. These sources are identified with massive close binaries in which a neutron star accretes material on to its surface. The observed pulsations in all of them, but one, are unambiguously associated with the spin period of the neutron star. Analysing the possible history of these pulsars, I conclude that the neutron stars in these systems undergo spherical accretion, and their evolutionary tracks in a previous epoch contained three instead of two states, namely ejector, supersonic propeller and subsonic propeller. An assumption about a supercritical value of the initial magnetic field of the neutron stars within this scenario is not necessary. Furthermore, I show that the scenario in which the neutron star in 2S 0114+650 is assumed to be a magnetar descendant encounters major difficulties in explaining the evolution of the massive companion. An alternative interpretation of the spin evolution of the neutron star in this system is presented and the problem raised by the association of the 104 s pulsations with the spin period of the neutron star is briefly discussed.