Signs of Magnetic Accretion in the X-ray Pulsar Binary GX 301-2

TL;DR

This paper investigates the magnetic properties of the accretion flow in the X-ray pulsar GX 301-2, proposing that magnetized accretion explains observed spin behaviors and suggesting the neutron star's surface magnetic field is around 4 x 10^{12} G.

Contribution

It introduces the concept that magnetized accretion flows can account for the spin-down rates in GX 301-2, challenging previous models that neglect magnetic effects in the accretion process.

Findings

Magnetized accretion flow increases spin-down torque.

Observed spin evolution aligns with magnetically controlled accretion.

Surface magnetic field estimated at ~4 x 10^{12} G.

Abstract

Observations of the cyclotron resonance scattering feature in the X-ray spectrum of GX 301-2 suggest that the surface field of the neutron star is B_CRSF ~ 4 x 10^{12}G. The same value has been derived in modelling the rapid spin-up episodes in terms of the Keplerian disk accretion scenario. However, the spin-down rate observed during the spin-down trends significantly exceeds the value expected in currently used spin-evolution scenarios. This indicates that either the surface field of the star exceeds 50 x B_CRSF, or a currently used accretion scenario is incomplete. We show that the above discrepancy can be avoided if the accreting material is magnetized. The magnetic pressure in the accretion flow increases more rapidly than its ram pressure and, under certain conditions, significantly affects the accretion picture. The spin-down torque applied to the neutron star in this case is larger than that evaluated within a non-magnetized accretion scenario. We find that the observed spin evolution of the pulsar can be explained in terms of the magnetically controlled accretion flow scenario provided the surface field of the neutron star is ~ B_CRSF.