[Paper Review] Massive X-ray binaries: New developments in the INTEGRAL era

I. Negueruela|arXiv (Cornell University)|Nov 29, 2004

Astrophysical Phenomena and Observations3 citations

TL;DR

This paper reviews new insights into massive X-ray binaries (MXBs) from the INTEGRAL mission, revealing a population of highly absorbed, transient MXBs with short outbursts and supergiant companions—challenging the traditional three-class classification. The discovery of these systems, including IGR J17391–3021 and IGR J17544–2619, suggests a larger, previously underestimated MXB population due to transient behavior and high absorption, reshaping understanding of MXB evolution and galactic source counts.

ABSTRACT

The study of massive X-ray binaries provides important observational diagnostics for a number of fundamental astrophysical issues, such as the evolution of massive stars, the stellar winds of massive stars, the formation of compact objects and accretion processes. More than three decades of study have led to a coherent picture of their formation and evolution and some understanding of the physical mechanisms involved. As more and more systems are discovered, this picture grows in complexity. Over the last two years, INTEGRAL has discovered a new population of massive X-ray binaries, characterised by absorbed spectra, which challenges some of our previous assumptions and guarantees that this will be a major subject of research for the near future.

Motivation & Objective

• To characterize the newly discovered population of massive X-ray binaries (MXBs) detected by INTEGRAL, particularly those with high absorption and short outbursts.
• To assess whether these new sources fit into the traditional classification of MXBs (classical, supergiant, Be/X-ray binaries) or represent a new evolutionary class.
• To evaluate the implications of transient behavior and high absorption for estimating the total Galactic MXB population.
• To identify optical counterparts of INTEGRAL sources and determine their stellar types to constrain the nature of the donor stars.
• To investigate the physical mechanisms behind the short outbursts and high absorption in these systems, particularly in relation to mass loss and accretion processes.

Proposed method

• Utilized INTEGRAL's hard X-ray capabilities to detect and analyze sources with highly absorbed spectra, particularly those showing transient X-ray activity.
• Combined XMM-Newton and Chandra observations to obtain precise source positions and identify optical counterparts with high spatial resolution.
• Analyzed X-ray lightcurves and pulse periods to confirm the presence of X-ray pulsars and determine spin periods (e.g., P_s = 228 s for IGR J16465–4507).
• Mapped source distributions in the P_orb / P_s diagram to compare new sources with classical MXB subclasses and identify deviations.
• Correlated X-ray spectral properties (e.g., absorption column density) with optical and infrared data to infer the nature of the donor stars and circumstellar environments.
• Used Doppler shift analysis of pulse arrival times and radial velocity measurements to derive orbital parameters where possible.

Experimental results

Research questions

• RQ1 Do the newly discovered INTEGRAL sources with high absorption and short outbursts conform to the classical three-class model of massive X-ray binaries?
• RQ2 What is the nature of the donor stars in the new transient MXBs, particularly those with supergiant companions and extremely short outbursts?
• RQ3 How does the high absorption in these sources affect their detectability and what does it imply about their circumstellar environments?
• RQ4 To what extent has the true population of massive X-ray binaries in the Galaxy been underestimated due to transient behavior and absorption?
• RQ5 Can the short outburst behavior observed in sources like IGR J17391–3021 and IGR J17544–2619 be explained by wind accretion or disk instabilities, and how does this differ from classical Be/X-ray binaries?

Key findings

• INTEGRAL discovered a new population of massive X-ray binaries characterized by high photoelectric absorption and extremely short X-ray outbursts (lasting less than 1 day), such as IGR J17391–3021 and IGR J17544–2619.
• The optical counterpart of IGR J17391–3021 was identified as an O8 Iaf supergiant, indicating that not all supergiant companions in transient MXBs behave like classical supergiant X-ray binaries (SXBs).
• IGR J16465–4507 was confirmed as a pulsating X-ray source with a spin period of 228 seconds, confirming its classification as a massive X-ray binary with a neutron star.
• The discovery of transient behavior in systems with supergiant donors—previously thought to be persistent—challenges the assumption that all SXBs are bright and steady, suggesting a larger hidden population.
• The concentration of new INTEGRAL sources toward the Galactic plane and spiral arms supports their origin in dense, massive stellar regions, consistent with MXB formation in high-mass star-forming regions.
• High absorption in these sources is likely due to dense circumstellar material, possibly from enhanced mass loss in the donor stars, as seen in IGR J16318–4848, which is associated with a peculiar companion.