Origin of young accreting neutron stars in high-mass X-ray binaries in supernova remnants

TL;DR

This paper proposes a model explaining young accreting neutron stars in supernova remnants by considering early fallback accretion and hysteresis effects, which can bypass the Ejector stage and initiate accretion rapidly.

Contribution

It introduces a rotational evolution model with hysteresis effects to explain the early appearance of accreting neutron stars in supernova remnants.

Findings

Fallback accretion can prevent the Ejector stage in young neutron stars.

A magnetic field of ~10^{12} G and initial spin of 0.1-0.2 s enable rapid accretion.

Accretion rates of 10^{14}-10^{15} g/s are sufficient to avoid the Ejector stage.

Abstract

Recently, several accreting neutron stars (NSs) in X-ray binary systems inside supernova remnants have been discovered. They represent a puzzle for the standard magneto-rotational evolution of NSs, as their ages ($\lesssim 10^5$ years) are much shorter than the expected duration of Ejector and Propeller stages preceding the onset of wind accretion. To explain appearance of such systems, we consider rotational evolution of NSs with early fallback accretion and asymmetry in forward/backward transitions between Ejector and Propeller stages (so-called hysteresis effect proposed by V. Shvartsman in 1970). It is shown that after a successful fallback episode with certain realistic values of the initial spin period, stellar wind properties, and magnetic field, a young NS may not enter the Ejector stage during its evolution which results in a relatively rapid initiation of accretion within the lifetime of a supernova remnant. For a standard magnetic field $\sim 10^{12}$~G and initial spin period $\sim 0.1$~--~0.2~s accretion rate $\gtrsim 10^{14}$~--~$10^{15}$~g~s$^{-1}$ is enough to avoid the Ejector stage.