[Paper Review] High Energy Phenomena in Supergiant X-ray Binaries

S. Chaty|arXiv (Cornell University)|May 12, 2010

Gamma-ray bursts and supernovae4 citations

TL;DR

This paper presents INTEGRAL satellite discoveries of a previously underappreciated population of supergiant high-mass X-ray binaries (sgXBs), revealing two distinct subclasses: highly absorbed, persistent wind-fed systems with long spin periods and dusty cocoon enshrouding the binary, and Supergiant Fast X-ray Transients (SFXTs) exhibiting short, intense flares due to clumpy wind accretion. The study establishes that these systems are linked to massive star-forming regions and represent key evolutionary stages in high-energy binary evolution, with implications for gamma-ray emission and compact object progenitors.

ABSTRACT

The INTEGRAL satellite has revealed a major population of supergiant High Mass X-ray Binaries in our Galaxy, revolutionizing our understanding of binary systems and their evolution. This population, constituted of a compact object orbiting around a massive and luminous supergiant star, exhibits unusual properties, either being extremely absorbed, or showing very short and intense flares. An intensive set of multi-wavelength observations has led us to reveal their nature, and to show that these systems are wind-fed accretors, closely related to massive star-forming regions. In this paper I describe the characteristics of these sources, showing that this newly revealed population is linked to the evolution of gamma-ray emitting massive stars with a compact companion.

Motivation & Objective

• To characterize the nature and properties of high-energy sources detected by the INTEGRAL satellite, particularly focusing on supergiant high-mass X-ray binaries (sgXBs).
• To determine the evolutionary pathways of these systems by identifying their companions, measuring orbital and spin periods, and assessing intrinsic absorption and circumstellar environments.
• To distinguish between two new subclasses: highly absorbed, persistent wind-fed systems and transient SFXTs with short flares.
• To link these systems to massive star-forming regions and assess their role in the formation of compact object binaries, including potential progenitors of gravitational wave sources.

Proposed method

• Multi-wavelength observations using ESO's 3.5m NTT (EMMI, SOFI) and VLT's 8m UT3 (VISIR) to obtain optical, near-infrared, and mid-infrared photometry and spectroscopy of 21 INTEGRAL sources.
• Spectral energy distribution (SED) fitting of optical, NIR, and MIR data to derive distances, identify companion stars, and detect circumstellar dust or gas components.
• Analysis of X-ray light curves and periodic modulations from INTEGRAL's IBIS and SPI instruments to measure spin and orbital periods and assess X-ray variability.
• Comparison of observed N_H–P_spin and N_H–P_orb correlations with theoretical models to distinguish between sgXBs and BeXBs.
• Use of Target of Opportunity (ToO) and Visitor mode observations to capture transient flares in SFXTs and enable rapid follow-up.
• Population synthesis modeling to explore the evolutionary pathways of these systems, particularly their role as precursors to common-envelope phases and compact object mergers.

Experimental results

Research questions

• RQ1 What is the nature of the newly discovered population of supergiant high-mass X-ray binaries revealed by INTEGRAL, and how do they differ from previously known HMXB classes?
• RQ2 What causes the extreme X-ray variability observed in Supergiant Fast X-ray Transients (SFXTs), and how does it relate to the orbital and wind structure of the binary system?
• RQ3 To what extent is the high intrinsic absorption in some sgXBs due to a dense, dusty cocoon surrounding the binary system, and how does this affect X-ray modulation?
• RQ4 How do the orbital parameters and accretion geometry in sgXBs correlate with their X-ray luminosity and spectral states?
• RQ5 What is the evolutionary significance of these systems in the context of massive binary evolution, particularly as potential progenitors of compact object mergers and gravitational wave sources?

Key findings

• INTEGRAL tripled the number of known Galactic supergiant X-ray binaries, identifying 15 new HMXBs with massive, luminous early-type companions.
• Twelve of the 15 identified HMXBs are wind-fed systems with long spin periods (139–5880 s) and orbital periods of 4–14 days, placing them in the upper region of the Corbet diagram.
• Three sources exhibit mid-infrared excesses indicative of a dust cocoon at ~1000 K, extending up to ~10 R* around the binary system, explaining their high intrinsic absorption.
• The SFXT class, exemplified by IGR J17544-2619, shows rapid X-ray flares lasting ~1 hour, with peak luminosity ~10^36 erg s⁻¹, recurring every ~7–100 days, consistent with clumpy wind accretion.
• The observed N_H–P_spin and N_H–P_orb correlations show that sgXBs and BeXBs are physically distinct, with sgXBs exhibiting higher absorption and longer spin periods.
• Population synthesis models suggest these systems may represent a precursor phase to the common-envelope evolution, with potential links to NS/NS or NS/BH coalescences and short-hard gamma-ray bursts.