Signs of magnetic accretion in X-ray pulsars

TL;DR

This paper investigates the spin-down mechanisms of accreting neutron stars, applying magnetic accretion theory to explain observed spin-down rates in the X-ray pulsar GX 301-2, emphasizing the role of magnetospheric radius.

Contribution

It introduces a method to evaluate the maximum spin-down torque and calculates the magnetospheric radius within a magnetic accretion framework, aligning theoretical predictions with observations.

Findings

Maximum spin-down torque formula derived

Magnetospheric radius smaller than canonical value explains observations

Theoretical spin-down rates match observed data for GX 301-2

Abstract

The spin-down mechanism of accreting neutron stars is discussed with an application to one of the best studied X-ray pulsars GX 301-2. We show that the maximum possible spin-down torque applied to a neutron star from the accretion flow can be evaluated as $K_{\rm sd}^{\rm (t)} = \mu^2/(r_{\rm m} r_{\rm cor})^{3/2}$. The spin-down rate of the neutron star in GX 301-2 can be explained provided the magnetospheric radius of the neutron star is smaller than its canonical value. We calculate the magnetospheric radius considering the mass-transfer in the binary system in the frame of the magnetic accretion scenario suggested by V.F. Shvartsman. The spin-down rate of the neutron star expected within this approach is in a good agreement with that derived from observations of GX 301-2.