Determination of wind-fed model parameters of neutron stars in high-mass X-ray binaries

TL;DR

This study models wind-fed neutron star high-mass X-ray binaries to understand accretion mechanisms, magnetic fields, and disk formation, providing insights into their variability and accretion regimes.

Contribution

It introduces a wind-fed binary model incorporating magnetic fields and classifies accretion regimes, enhancing understanding of HMXB variability and accretion processes.

Findings

Derived system parameters align with direct accretion in most cases.

Identified five regimes of disk formation based on wind velocity.

Some systems may transition from wind accretion to RLOF regimes.

Abstract

We have studied several neutron star high-mass X-ray binaries (HMXBs) with super-giant (SG) companions using a wind-fed binary model associated with the magnetic field. By using the concept of torque balance, the magnetic field parameter determines the mass accretion rate. This would help us to consider the relationship between wind velocity and mass-loss rate. These parameters significantly improve our understanding of the accretion mechanism. The wind velocity is critical in determining the X-ray features. This can be used to identify the ejection process and the stochastic variations in their accretion regimes. However, even in systems with a long orbital period, an accretion disk can be created when the wind velocity is slow. This will allow the HMXB of both types, SG and Be, to be better characterised by deriving accurate properties from these binaries. In addition, we have performed segmentation in the parameter space of donors intended for several SG-HMXB listed in our sample set. The parameter space can be categorised into five regimes, depending on the possibility of disk formation associated with accretion from the stellar wind. This can give a quantitative clarification of the observed variability and the properties of these objects. For most of the systems, we show that the derived system parameters are consistent with the assumption that the system is emitting X-rays through direct accretion. However, there are some sources (LMC X-4, Cen X-3 and OAO1657-415) that are not in the direct accretion regime, although they share similar donor parameters. This may indicate that these systems are transitioning from a normal wind accretion phase to partial RLOF regimes.