On the maximum accretion luminosity of magnetized neutron stars: connecting X-ray pulsars and ultraluminous X-ray sources

Mushtukov, Alexander A.; Suleimanov, V.; Tsygankov, Sergey S.; Poutanen, Juri

doi:10.1093/mnras/stv2087

Cited by 210 publications

(241 citation statements)

References 42 publications

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“…Therefore, here we will concentrate on the quite likely case when the total luminosity is above the Eddington limit but the disc is everywhere subcritical. Column luminosity is not strictly limited by the classical Eddington limit because of geometrical and opacity effects (Basko & Sunyaev 1976;Mushtukov et al 2015). It is quite possible for a neutron star to exceed the Eddington limit by a factor of ∼ 10 2 − 10 3 .…”

Section: Introductionmentioning

confidence: 99%

Super-Eddington accretion on to a magnetized neutron star

Chashkina

Abolmasov

Poutanen

2017

Monthly Notices of the Royal Astronomical Society

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Most of ultraluminous X-ray sources are thought to be objects accreting above their Eddington limits. In the recently identified class of ultraluminous X-ray pulsars, accretor is a neutron star and thus has a fairly small mass with a small Eddington limit. The accretion disc structure around such an object affects important observables such as equilibrium period, period derivative and the size of the magnetosphere. We propose a model of a nearly-standard accretion disc interacting with the magnetosphere only in a thin layer near the inner disc rim. Our calculations show that the size of the magnetosphere may be represented as the classical Alfvén radius times a dimensionless factor ξ which depends on the disc thickness only. In the case of radiation-pressure-dominated disc, the size of the magnetosphere does not depend on the mass accretion rate. In general, increasing the disc thickness leads to a larger magnetosphere size in units of the Alfvén radius. For large enough mass accretion rates and magnetic moments, it is important to take into account not only the pressure of the magnetic field and the radiation pressure inside the disc, but also the pressure of the radiation produced close to the surface of the neutron star in accretion column. The magnetospheric size may increase by up to factor of two as a result of the effects related to the disc thickness and the irradiation from the central source. Accounting for these effects reduces the estimate of the neutron star magnetic moment by a factor of several.

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Section: Introductionmentioning

confidence: 99%

Super-Eddington accretion on to a magnetized neutron star

Chashkina

Abolmasov

Poutanen

2017

Monthly Notices of the Royal Astronomical Society

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“…Depending on accretion column height and NS compactness, the direct flux from the accretion column is eclipsed, or strongly am- plified due to gravitational lensing. High accretion columns, which are expected at high mass accretion rates (Basko & Sunyaev 1976;Mushtukov et al 2015a), can be eclipsed by NS of sufficiently large radii only (see Fig. 11).…”

Section: Beam Patterns Of Bright X-ray Pulsarsmentioning

confidence: 90%

“…(2) The relation between accretion column height and luminosity is defined by the accretion channel base geometry and opacity across B-field lines κ ⊥ , which depends on magnetic field strength. There is an approximate relation between column height and luminosity (Mushtukov et al 2015a):…”

Section: Accretion Luminosity and Accretion Column Heightmentioning

confidence: 99%

“…which was derived for accretion columns in a diffusion approximation (Mushtukov et al 2015a). Because the accretion column can be considered as a set of point sources of luminosity g(h)dh and the distribution of incoming photon energy flux over the surface can be calculated as…”

Section: Radiation From the Accretion Columnmentioning

confidence: 99%

“…It very likely that their central engine is formed by accretion columns confined by a strong magnetic field (Mushtukov et al 2015a). However, in case of ULXs powered by accreting NSs the accretion flow at the NS magnetosphere is optically thick and the central engine is hidden behind it.…”

Section: Pulsating Ulxsmentioning

confidence: 99%

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On the radiation beaming of bright X-ray pulsars and constraints on neutron star mass–radius relation

Mushtukov

Verhagen

Tsygankov

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The luminosity of accreting magnetised neutron stars can largely exceed the Eddington value due to appearance of accretion columns. The height of the columns can be comparable to the neutron star radius. The columns produce the X-rays detected by the observer directly and illuminate the stellar surface, which reprocesses the X-rays and causes additional component of the observed flux. The geometry of the column and the illuminated part of the surface determines the radiation beaming. Curved spacetime affects the angular flux distribution. We construct a simple model of the beam patterns formed by direct and reflected flux from the column. We take into account the possibility of appearance of accretion columns, whose height is comparable to the neutron star radius. We argue that depending on the compactness of the star the flux from the column can be either strongly amplified due to gravitational lensing, or significantly reduced due to column eclipse by the star. The eclipses of high accretion columns result in specific features in pulse profiles. Their detection can put constraints on the neutron star radius. We speculate that column eclipses are observed in X-ray pulsar V 0332+53, leading us to the conclusion of large neutron star radius in this system (∼ 15 km if M ∼ 1.4M ). We point out that the beam pattern can be strongly affected by scattering in the accretion channel at high luminosity, which has to be taken into account in the models reproducing the pulse profiles.

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Ultraluminous X‐ray sources: Three exciting years

Bachetti

2016

Astron Nachr

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The extreme extragalactic sources known as Ultraluminous X-ray Sources (ULX) represent a unique testing environment for compact objects population studies and the accretion process. Their nature has long been disputed. Their luminosity, well above the Eddington luminosity for a stellar-mass black hole, can imply the presence of an intermediate-mass black hole or a stellar black hole accreting above the Eddington limit. Both these interpretations are important to understand better the accretion process and the evolution of massive black holes. The last few years have seen a dramatic improvement of our knowledge of these sources. In particular, the super-Eddington interpretation for the bulk of the ULX population has gained a strong consensus. Nonetheless, exceptions to this general trend do exist, and in particular one ULX was shown to be a neutron star, and another was shown to be a very likely IMBH candidate. In this paper, I will review the progress done in the last few years.

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On the maximum accretion luminosity of magnetized neutron stars: connecting X-ray pulsars and ultraluminous X-ray sources

Cited by 210 publications

References 42 publications

Super-Eddington accretion on to a magnetized neutron star

Super-Eddington accretion on to a magnetized neutron star

On the radiation beaming of bright X-ray pulsars and constraints on neutron star mass–radius relation

Ultraluminous X‐ray sources: Three exciting years

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