Revealing the nature of high-mass X-ray binaries through multi-wavelength and statistical analyses

TL;DR

This paper uses multi-wavelength and statistical analyses to explore the nature, classification, and evolution of high-mass X-ray binaries, revealing new insights into their sub-classes and their relation to star formation.

Contribution

It introduces new diagnostic tools for classifying HMXBs and provides the first spatial correlation analysis linking HMXBs with OB star-forming regions.

Findings

SFXTs may be evolutionarily linked to BEXBs and SGXBs.

HMXBs are spatially correlated with OB star-forming complexes.

Different HMXB sub-classes show distinct accretion mechanisms.

Abstract

We summarize the results of our long-running campaign to help understand the nature of high-mass X-ray binaries (HMXBs), emphasizing recent Suzaku observations of IGR J16207-5129 and IGR J17391-3021. Thanks to the expanding ranks of HMXBs in our Galaxy, we are able to perform more reliable statistical analyses on the three currently-known sub-classes of HMXB: those with supergiant companions (SGXBs); those with Be companions (BEXBs); and the enigmatic Supergiant Fast X-ray Transients (SFXTs). We discuss new diagnostic tools, akin to the "Corbet diagram," in which HMXBs tend to segregate based on their dominant accretion mechanism. We show how SFXTs span across the divided populations of BEXBs and SGXBs, bolstering the intriguing possibility that some SFXTs represent an evolutionary link. The use of HMXBs as tracers of recent massive star formation is revisited as we present the first ever spatial correlation function for HMXBs and OB star-forming complexes. Our results indicate that at distances less than a few kpc from a given HMXB, it is more likely to have neighbors that are known massive-star forming regions as opposed to objects drawn from random distributions. The characteristic scale of the correlation function holds valuable clues to HMXB evolutionary timescales.