Characteristics and evolution of Be-type high mass X-ray binaries as potential Ultraluminous X-ray Sources

TL;DR

This paper investigates how Be-type high mass X-ray binaries can evolve into ultraluminous X-ray sources, estimating their potential duration as ULXs and identifying conditions that favor this transition.

Contribution

It introduces a model to estimate when BeHMXBs exceed Eddington luminosity and explores their evolution into ULXs, highlighting the significance of dense Be star disks.

Findings

BeHMXBs can be ULXs for about 1 million years.

Many BeHMXBs have the potential to become ULXs during evolution.

ULXs may often originate from evolved BeHMXBs with dense disks.

Abstract

Some ultraluminous X-ray sources (ULXs) exhibit X-ray pulses, and their central sources are thought to be neutron stars. It has also been suggested that some are transient sources with Be-type donors. In this study, we use the mass accretion model of a Be-type high mass X-ray binary (BeHMXB) to estimate the conditions under which a giant X-ray burst caused by a BeHMXB exceeds the Eddington luminosity. Moreover, we investigate the duration for which BeHMXBs can be observed as transient ULXs with bursts above the Eddington luminosity during binary evolutions. The results indicate that BeHMXBs could be ULXs for a typical duration of approximately 1 Myr. Comparisons with nearby observed BeHMXBs indicate that many binary systems have the potential to become ULXs during their evolution. Particularly, a BeHMXB system tends to become a ULX when the Be donor has a dense deccretion disc aligned with the orbital plane. Because BeHMXBs are very common objects and a significant number of them can become ULXs, we conclude that a reasonable fraction of the observed ULXs could consist of evolved BeHMXBs.