# Ultra-luminous X-ray sources as neutron stars propelling and accreting at super-critical rates in high-mass X-ray binaries

## TL;DR

This paper proposes an evolutionary model where neutron stars in high-mass X-ray binaries can propel matter at super-critical rates, explaining the nature of ultra-luminous X-ray sources and their pulsating counterparts.

## Contribution

It introduces a self-consistent magnetosphere-disk interaction model to explain ULXs as neutron stars propelling matter at super-critical rates, linking non-pulsating and pulsating ULXs.

## Key findings

- Non-pulsating ULXs can be neutron stars propelling matter at super-critical rates.
- Pulsating ULXs are evolved, super-critical accreting neutron stars.
- The model constrains neutron star magnetic fields and spin evolution.

## Abstract

Ultra-luminous X-ray sources (ULXs) are off-nuclear point sources in nearby galaxies with luminosities well exceeding the Eddington limit for stellar-mass objects. It has been recognized after the discovery of pulsating ULXs (PULXs) that a fraction of these sources could be accreting neutron stars in high-mass X-ray binaries (HMXBs) though the majority of ULXs are lacking in coherent pulsations. The earliest stage of some HMXBs may harbor rapidly rotating neutron stars propelling out the matter transferred by the massive companion. The spin-down power transferred by the neutron-star magnetosphere to the accretion disk at this stage can well exceed the Eddington luminosities and the system appears as a non-pulsating ULX. In this picture, PULXs appear as super-critical mass-accreting descendants of non-pulsating ULXs. We present this evolutionary scenario within a self-consistent model of magnetosphere-disk interaction and discuss the implications of our results on the spin and magnetic field of the neutron star.