Stellar wind accretion and accretion disk formation: Applications to neutron star high-mass X-ray binaries

Abstract. A fraction of high-mass X-ray binaries are supergiant fast X-ray transients. These systems have on average low X-ray luminosities, but display short flares during which their X-ray luminosity rises by a few orders of magnitude. The leading model for the physics governing this X-ray behaviour suggests that the winds of the donor OB supergiants are magnetized. In agreement with this model, the first spectropolarimetric observations of the SFXT IGR J11215-5952 using the FORS 2 instrument at the Very Large Telescope indicate the presence of a kG longitudinal magnetic field. Based on these results, it seems possible that the key difference between supergiant fast X-ray transients and other high-mass X-ray binaries are the properties of the supergiant’s stellar wind and the physics of the wind’s interaction with the neutron star magnetosphere.

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Accretion from Stellar Winds

International Astronomical Union Colloquium ◽

10.1017/s0252921100103306 ◽

1988 ◽

Vol 103 ◽

pp. 149-160

Author(s):

Mario Livio

Keyword(s):

Angular Momentum ◽

Inhomogeneous Medium ◽

Accretion Disk ◽

Stellar Wind ◽

Optical Observations ◽

Stellar Winds ◽

X Ray ◽

Disk Formation ◽

X Ray Binaries

AbstractRecent calculations have demonstrated that accretion from a stellar wind is very probably unsteady. The average rate of accretion of angular momentum is lower by about a factor 5 than the rate at which angular momentum is deposited into the Bondi-Hoyle accretion cylinder. This makes disk formation from wind accretion very difficult, in particular in the case of massive x-ray binaries. A combination of x-ray, uv and optical observations of symbiotic and related systems, as well as spin-up information on x-ray binaries, can be used to determine whether an accretion disk does form. Such observations can provide us with valuable information on the process of accretion from an inhomogeneous medium.

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Hardness Ratio in Evolving Low-Mass X-ray Binary Systems

Symposium - International Astronomical Union ◽

10.1017/s0074180900160723 ◽

1987 ◽

Vol 125 ◽

pp. 199-199

Author(s):

J. Shaham ◽

M. Tavani

Keyword(s):

Neutron Star ◽

Accretion Disk ◽

Binary Systems ◽

Spectral Component ◽

Soft Component ◽

Hard Component ◽

X Ray ◽

Low Mass ◽

Additional Support ◽

X Ray Binaries

Spectral observations of low-mass X-ray binaries (LMXBs) show that the soft component usually dominates over the hard one. These results provide additional support to an interpretation based on models of LMXBs in which the neutron star while, on the average, spinning up, is also experiencing a spinning down torque. Under these conditions, a fraction of the luminosity associated with the gravitational release of energy on the surface of the accreting neutron star may manifest itself as luminosity originating in the inner part of the accretion disk. It is probably possible to separate the two contributions; the stellar luminosity can be associated with the hard component of the spectrum and the disk luminosity, related to the exchange of energy due to the torque between the rapidly spinning neutron star and the accretion disk, can be associated with the soft spectral component.

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Mass transfer on a nuclear timescale in models of supergiant and ultra-luminous X-ray binaries

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935453 ◽

2019 ◽

Vol 628 ◽

pp. A19 ◽

Cited By ~ 6

Author(s):

M. Quast ◽

N. Langer ◽

T. M. Tauris

Keyword(s):

Mass Transfer ◽

Black Hole ◽

Neutron Star ◽

Roche Lobe ◽

High Mass ◽

X Rays ◽

X Ray ◽

Mass Ratios ◽

X Ray Binaries ◽

Eddington Limit

Context. The origin and number of the Galactic supergiant X-ray binaries is currently not well understood. They consist of an evolved massive star and a neutron star or black-hole companion. X-rays are thought to be generated from the accretion of wind material donated by the supergiant, while mass transfer due to Roche-lobe overflow is mostly disregarded because the high mass ratios of these systems are thought to render this process unstable. Aims. We investigate how the proximity of supergiant donor stars to the Eddington limit, and their advanced evolutionary stage, may influence the evolution of massive and ultra-luminous X-ray binaries with supergiant donor stars (SGXBs and ULXs). Methods. We constructed models of massive stars with different internal hydrogen and helium gradients (H/He gradients) and different hydrogen-rich envelope masses, and exposed them to slow mass-loss to probe the response of the stellar radius. In addition, we computed the corresponding Roche-lobe overflow mass-transfer evolution with our detailed binary stellar evolution code, approximating the compact objects as point masses. Results. We find that a H/He gradient in the layers beneath the surface, as it is likely present in the well-studied donor stars of observed SGBXs, can enable mass transfer in SGXBs on a nuclear timescale with a black-hole or a neutron star accretor, even for mass ratios in excess of 20. In our binary evolution models, the donor stars rapidly decrease their thermal equilibrium radius and can therefore cope with the inevitably strong orbital contraction imposed by the high mass ratio. We find that the orbital period derivatives of our models agree well with empirical values. We argue that the SGXB phase may be preceded by a common-envelope evolution. The envelope inflation near the Eddington limit means that this mechanism more likely occurs at high metallicity. Conclusion. Our results open a new perspective for understanding that SGBXs are numerous in our Galaxy and are almost completely absent in the Small Magellanic Cloud. Our results may also offer a way to find more ULX systems, to detect mass transfer on nuclear timescales in ULX systems even with neutron star accretors, and shed new light on the origin of the strong B-field in these neutron stars.

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Modelling decretion discs in Be/X-ray binaries

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1757 ◽

2019 ◽

Cited By ~ 4

Author(s):

R O Brown ◽

M J Coe ◽

W C G Ho ◽

A T Okazaki

Keyword(s):

Neutron Star ◽

Orbital Period ◽

Major Axis ◽

High Mass ◽

Model Parameters ◽

Be Stars ◽

Semi Major Axis ◽

X Ray ◽

Smoothed Particle ◽

X Ray Binaries

Abstract As the largest population of high mass X-ray binaries, Be/X-ray binaries provide an excellent laboratory to investigate the extreme physics of neutron stars. It is generally accepted that Be stars possess a circumstellar disc, providing an additional source of accretion to the stellar winds present around young hot stars. Interaction between the neutron star and the disc is often the dominant accretion mechanism. A large amount of work has gone into modelling the properties of these circumstellar discs, allowing for the explanation of a number of observable phenomena. In this paper, smoothed particle hydroynamics simulations are performed whilst varying the model parameters (orbital period, eccentricity, the mass ejection rate of the Be star and the viscosity and orientation of the disc). The relationships between the model parameters and the disc’s characteristics (base gas density, the accretion rate of the neutron star and the disc’s size) are presented. The observational evidence for a dependency of the size of the Be star’s circumstellar disc on the orbital period (and semi-major axis) is supported by the simulations.

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Early neutron star evolution in high-mass X-ray binaries

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa675 ◽

2020 ◽

Vol 494 (1) ◽

pp. 44-49 ◽

Cited By ~ 2

Author(s):

Wynn C G Ho ◽

M J P Wijngaarden ◽

Nils Andersson ◽

Thomas M Tauris ◽

F Haberl

Keyword(s):

Magnetic Field ◽

Neutron Star ◽

Thermal Emission ◽

Equilibrium Phase ◽

High Mass ◽

X Ray ◽

Spin Period ◽

Long Duration ◽

X Ray Binaries ◽

The Magnetic Field

ABSTRACT The application of standard accretion theory to observations of X-ray binaries provides valuable insights into neutron star (NS) properties, such as their spin period and magnetic field. However, most studies concentrate on relatively old systems, where the NS is in its late propeller, accretor, or nearly spin equilibrium phase. Here, we use an analytic model from standard accretion theory to illustrate the evolution of high-mass X-ray binaries (HMXBs) early in their life. We show that a young NS is unlikely to be an accretor because of the long duration of ejector and propeller phases. We apply the model to the recently discovered ∼4000 yr old HMXB XMMU J051342.6−672412 and find that the system’s NS, with a tentative spin period of 4.4 s, cannot be in the accretor phase and has a magnetic field B > a few × 1013 G, which is comparable to the magnetic field of many older HMXBs and is much higher than the spin equilibrium inferred value of a few × 1011 G. The observed X-ray luminosity could be the result of thermal emission from a young cooling magnetic NS or a small amount of accretion that can occur in the propeller phase.

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Probing the stellar wind geometry in Vela X-1 with infrared interferometry

Proceedings of the International Astronomical Union ◽

10.1017/s174392131201959x ◽

2012 ◽

Vol 8 (S290) ◽

pp. 197-198

Author(s):

Élodie Choquet ◽

Pierre Kervella ◽

Jean-Baptiste Le Bouquin ◽

Antoine Mérand ◽

Xavier Haubois ◽

...

Keyword(s):

Neutron Star ◽

High Mass ◽

Resolution Limit ◽

X Ray ◽

Upper Limit ◽

Accretion Process ◽

Massive Neutron Star ◽

Infrared Interferometry ◽

X Ray Binaries ◽

K Band

AbstractHigh-mass X-ray Binaries (HMXBs) are keys to study stellar remnants that are otherwise extremely faint and difficult to observe when isolated. Vela X-1 is a well-known eclipsing HMXB composed of a very massive neutron star orbiting a B0.5I supergiant with a period of 9 days. The supergiant wind is the main feeding material for the accreting neutron star, and its properties are of prime interest to understand the physics at stakes in the accretion process.In order to characterize the geometry and physical properties of the dense wind at a scale of a few stellar radii, we obtained infrared interferometric observations of Vela X-1 in 2010 using the VLTI/AMBER instrument in the K band (2.2 μm), and in 2012 using the VLTI/PIONIER instrument in the H band (1.6 μm).Although the apparent disk of the supergiant and the orbital separation of the two objects are beyond the present resolution limit of the VLTI, the K-band observations partially resolve the wind envelope on the two longest baselines. We were able to measure the radius of 265±82 R⊙ for the circumstellar wind at a temperature of 1300 K, assuming a distance of 1.9 kpc. The H-band observations do not resolve the system, and we were able to set an upper limit of 112 R⊙ for the envelope radius at a temperature of 1800 K.

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Color–color diagrams as tools for assessment of the variable absorption in high mass X-ray binaries

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039183 ◽

2020 ◽

Vol 643 ◽

pp. A109

Author(s):

V. Grinberg ◽

M. A. Nowak ◽

N. Hell

Keyword(s):

Stellar Wind ◽

Binary Systems ◽

Compact Object ◽

Spectral Shape ◽

High Mass ◽

Line Of Sight ◽

Current Generation ◽

X Ray ◽

Partial Covering ◽

X Ray Binaries

High mass X-ray binaries hold the promise of allowing us to understand the structure of the winds of their supermassive companion stars by using the emission from the compact object as a backlight to evaluate the variable absorption in the structured stellar wind. The wind along the line of sight can change on timescales as short as minutes and below. However, such short timescales are not available for the direct measurement of absorption through X-ray spectroscopy with the current generation of X-ray telescopes. In this paper, we demonstrate the usability of color–color diagrams for assessing the variable absorption in wind accreting high mass X-ray binary systems. We employ partial covering models to describe the spectral shape of high mass X-ray binaries and assess the implication of different absorbers and their variability on the shape of color–color tracks. We show that in taking into account, the ionization of the absorber, and in particular accounting for the variation of ionization with absorption depth, is crucial to describe the observed behavior well.

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Evidence from high-mass X-ray binaries that Galactic WR components of WR+O binaries end their life with a supernova explosion

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937253 ◽

2020 ◽

Vol 636 ◽

pp. A99 ◽

Cited By ~ 3

Author(s):

D. Vanbeveren ◽

N. Mennekens ◽

E. P. J. van den Heuvel ◽

J. Van Bever

Keyword(s):

Black Hole ◽

Neutron Star ◽

Supernova Explosion ◽

Solar Neighborhood ◽

High Mass ◽

Population Number ◽

X Ray ◽

Theoretical Population ◽

X Ray Binaries

Context. Theoretical population number studies of binaries with at least one black hole (BH) component obviously depend on whether or not BHs receive a (natal) kick during their formation. Aims. Several observational facts seem to indicate that BHs do indeed receive a kick during their formation. In the present paper, we discuss additional evidence of this. Methods. The progenitors of wind-fed high-mass X-ray binaries (HMXB) with a BH component (BH HMXB) are WR+OB binaries where the Wolf–Rayet (WR) star will finally collapse and form the BH. Starting from the observed population of WR+OB binaries in the solar neighborhood, we predict the population of wind-fed BH HMXBs as a function of the BH-natal kick. Results. The simulations reveal that when WR stars collapse into a BH with a zero or low kick, we should expect 100 or more wind-fed BH HMXBs in the solar neighborhood, whereas only one is observed (Cyg X-1). We consider this as evidence that either WR components in binaries end their life as a neutron star or that they collapse into BHs, both accompanied by a supernova explosion imparting significant (natal) kicks.

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