MAD-Accretion Scenario in High-Mass X-Ray Binaries with Neutron Stars

TL;DR

This paper explores the magnetically arrested disk (MAD) accretion scenario in high-mass X-ray binaries with neutron stars, emphasizing how stellar wind properties influence neutron star spin periods.

Contribution

It formulates criteria for MAD accretion in HMXBs and estimates how stellar wind magnetization affects neutron star equilibrium rotation periods.

Findings

Neutron star spin period increases with wind magnetization.

MAD accretion criteria are established for HMXBs.

Equilibrium periods can reach tens of thousands of seconds.

Abstract

The wind-fed accretion of gas with an intrinsic magnetic field onto neutron stars in high-mass X-ray binaries (HMXBs) is discussed. The criteria for the implementation of quasi-spherical accretion in the system, the formation of a Keplerian accretion disk and a non-Keplerian magnetically arrested disk (MAD-accretion scenario) are formulated. It is shown that the period of the equilibrium rotation of a neutron star in the MAD-accretion scenario, in addition to the parameters of the binary system, is also determined by the velocity, temperature, and degree of magnetization of the stellar wind of its massive companion. Within the hypothesis of the equilibrium rotation, we have estimated the parameters of the stellar wind for the most fully-studied quasi-equilibrium accreting pulsars in the HMXBs corresponding to the criteria for the MAD-accretion scenario implementation. We show that the period of the equilibrium rotation of a neutron star in the system, all other things being equal, increases with the growth of the magnetization degree of the stellar wind component of its massive companion flowing out in the plane of the system's orbit. Therefore, the periods of accreting pulsars in systems with similar parameters can differ from each other by several orders of magnitude and, under favorable conditions, reach values of several thousand and even tens of thousands of seconds.