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 700-10000 s. These sources are identified with massive close binaries in which a neutron star accretes material onto its surface. The observed pulsations in all of them, but one, are unambiguously associated with the spin period of the neutron star. Analyzing 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 association of the 10000 s pulsations with the spin period of the neutron star is briefly discussed.Comment: 7 pages, 2 tables, accepted for publication in MNRA

High-mass X-ray binaries in the Milky Way

“…These authors developed in details the previously proposed idea of the so-called "subsonic accretion regime" (Davies and Pringle, 1981;Ikhsanov, 2007). According to Elsner and Lamb (1977), the wind material halted at R acc is able to fall freely and accrete at the rate indicated by Eq.…”

Exploring the Small Magellanic Cloud to the Faintest X-Ray Fluxes: Source Catalog, Timing, and Spectral Analysis

“…A theoretical investigation into long-period X-ray pulsars by Ikhsanov (2006) postulated a modification to NS spin evolution that divides the propellor phase into supersonic and subsonic propellor phases. They report that this refinement removes the ∼500 s barrier in specific circumstances and reconciles the standard theory of close-binary evolution with the undoubted existence of long-period HMXB pulsars.…”

“…They report that this refinement removes the ∼500 s barrier in specific circumstances and reconciles the standard theory of close-binary evolution with the undoubted existence of long-period HMXB pulsars. Ikhsanov (2006) also gives two scenarios that lead to X-ray pulsars with periods >1000 s. First, if the NS accretes spherically the spin-orbit equilibrium period is an order of magnitude longer than for disk-fed accretion. Second, if the mass-donor star has recently increased its mass-loss rate, a slow-rotating NS companion (that had spun-down to equilibrium spin in a more tenuous wind) will be re-activated as a long-period X-ray pulsar.…”

“…Continued monitoring and optical counterpart studies will be important to reveal whether the spin-orbit equilibrium for trans-P max pulsars differs from pulsars in the < 500 s range, testing the suggestion of Ikhsanov (2006) that different physics comes into play. A large number of hard point sources in the SMC are still unidentified and could plausibly be X-ray pulsars.…”

Retrograde wind accretion – an alternative mechanism for long spin period of SFXTs

“…If the system undergoes a spherical accretion and three epochs, i.e. the ejector, supersonic propeller, and subsonic propeller epoch, the conditions under which a longer period can be achieved may be relaxed (Ikhsanov 2001(Ikhsanov , 2007.…”