Hunting for Magnetars in High Mass X-ray Binaries. The Case of SuperGiant Fast X-Ray Transients

TL;DR

This paper explores how wind accretion and magnetic barriers in high mass X-ray binaries can cause large luminosity swings, suggesting SFXTs may host magnetar-like neutron stars and serve as unique laboratories for studying accreting magnetars.

Contribution

It introduces a model linking luminosity variability in SFXTs to magnetic and centrifugal barriers, proposing these systems may contain magnetar-like neutron stars.

Findings

Large luminosity swings (~10^4) can result from regime transitions.

SFXTs with slow-spinning neutron stars likely have magnetar-like fields.

SFXTs offer a new way to study accreting magnetars.

Abstract

In this paper we summarize some aspects of the wind accretion theory in high mass X-ray binaries hosting a magnetic neutron star and a supergiant companion. In particular, we concentrate on the different types of interaction between the inflowing wind matter and the neutron star magnetosphere that are relevant when accretion of matter onto the neutron star surface is largely inhibited; these include inhibition by the centrifugal and magnetic barriers. We show that very large luminosity swings (~10^4 or more on time scales as short as hours) can result from transitions across different regimes. This scenario is then applied to the activity displayed by supergiant fast X-ray transients (SFXTs), a new class of high mass X-ray binaries in our galaxy recently discovered with INTEGRAL. According to this interpretation we argue that SFXTs which display very large luminosity swings and host a slowly spinning neutron star are expected to be characterized by magnetar-like fields. Supergiant fast X-ray transients might thus provide a unique opportunity to detect and study accreting magnetars in binary systems.