Radial modes of levitating atmospheres around Eddington luminosity neutron stars

Bollimpalli, D. A.; Kluźniak, W.

doi:10.1093/mnras/stx2140

Cited by 6 publications

(13 citation statements)

References 34 publications

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“…These simulations could have astrophysical interest in the context of high frequency QPOs in black hole, low-mass X-ray binaries. Our simulation shows local oscillations at the breathing frequency predicted theoretically (Silbergleit et al 2001;Bollimpalli & Kluźniak 2017). A qualitative, as well as quantitative, analysis of the simulation confirms the identity of the oscillation.…”

Section: Discussionsupporting

confidence: 79%

“…The results described below are based on our radiative, viscous, relativistic hydrodynamic simulations of geometrically thin black hole accretion disks . In this paper we unambiguously identify the presence in the simulations of a particular type of local, thin-disk oscillations, corresponding to the well studied breathing modes of accretion tori (Blaes et al 2006) and spherical (or planeparallel) atmospheres (Bollimpalli & Kluźniak 2017).…”

Section: Introductionmentioning

confidence: 73%

“…In our simulations the disk seems to execute such oscillations at all radii, each at its own frequency. the formula (Silbergleit et al 2001;Kato 2016;Bollimpalli & Kluźniak 2017)…”

Section: Characteristic Frequenciesmentioning

confidence: 99%

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Breathing oscillations in a global simulation of a thin accretion disc

Mishra

Kluźniak

Fragile

2018

Monthly Notices of the Royal Astronomical Society

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We study the oscillations of an axisymmetric, viscous, radiative, general relativistic hydrodynamical simulation of a geometrically thin disk around a non-rotating, 6.62 M black hole. The numerical setup is initialized with a Novikov-Thorne, gas-pressuredominated accretion disk, with an initial mass accretion rate of m = 0.01 L Edd /c 2 (where L Edd is the Eddington luminosity and c is the speed of light). Viscosity is treated with the α-prescription. The simulation was evolved for about 1000 Keplerian orbital periods at three Schwarzschild radii (ISCO radius). Power density spectra of the radial and vertical fluid velocity components, the total (gas + radiation) midplane pressure, and the vertical component of radiative flux from the photosphere, all reveal strong power at the local breathing oscillation frequency. The first, second and third harmonics of the breathing oscillation are also clearly seen in the data. We quantify the properties of these oscillations by extracting eigenfunctions of the radial and vertical velocity components and total pressure. This confirms that these oscillations are associated with breathing motion.

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Section: Discussionsupporting

confidence: 79%

Section: Introductionmentioning

confidence: 73%

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Breathing oscillations in a global simulation of a thin accretion disc

Mishra

Kluźniak

Fragile

2018

Monthly Notices of the Royal Astronomical Society

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“…Radial oscillations of levitating atmospheres have been previously investigated for special cases (Abarca & Kluźniak 2016;Bollimpalli & Kluźniak 2017), and the current paper aims to present a general study of these oscillations, including radiation drag in the relativistic regime. Before turning to rigorous calculations (Section 3 and following), we present a heuristic derivation of the fundamental mode frequency of the levitating atmosphere.…”

Section: Fundamentals Of Levitating Atmosphere Oscillationsmentioning

confidence: 99%

“…(2), and the radius of equilibrium follows as 1 The higher radial modes are more difficult to derive, as pressure variations play a role in determining the oscillatory motion. For example, the next higher mode is a breathing mode in which the oscillatory motion can be described as expansion away and contraction towards the ECS, with the (only) node at the ECS (Bollimpalli & Kluźniak 2017). (Abramowicz et al 1990;Stahl et al 2013)…”

Section: Fundamentals Of Levitating Atmosphere Oscillationsmentioning

confidence: 99%

Atmospheric oscillations provide simultaneous measurement of neutron star mass and radius

Bollimpalli

Wielgus

Abarca

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Neutron stars with near-Eddington observable luminosities were shown to harbour levitating atmospheres, suspended above their surfaces. We report a new method to simultaneously measure the mass and radius of a neutron star based on oscillations of such atmospheres. In this paper, we present an analytic derivation of a family of relativistic, oscillatory, spherically symmetric eigenmodes of the optically and geometrically thin levitating atmospheres, including the damping effects induced by the radiation drag. We discover characteristic maxima in the frequencies of the damped oscillations and show that from a measurement of the frequency maximum and of the luminosity one can determine the mass and radius of the neutron star. In addition to the stellar parameters, observation of the variation of the oscillation frequencies with flux would allow us to estimate the stellar luminosity and therefore the distance to the source with an accuracy of a few per cent. We also show that the ratio of any two undamped eigenfrequencies depends only on the adiabatic index of the atmosphere, while for the damped eigenfrequencies, this ratio varies with the luminosity. The damping coefficient is independent of the mode number of the oscillations. Signatures of the dynamics of such atmospheres will be reflected in the source's X-ray light curves.

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Relativistic, axisymmetric, viscous, radiation hydrodynamic simulations of geometrically thin discs. II. Disc variability

Mishra

Kluźniak

Fragile

2020

Monthly Notices of the Royal Astronomical Society

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An analysis of two-dimensional viscous, radiation hydrodynamic numerical simulations of thin α-disks around a stellar mass black hole reveals multiple robust, coherent oscillations. Our disk models are initialized on both the gas- and radiation-pressure-dominated branches of the thermal equilibrium curve, with mass accretion rates between $\dot{M} = 0.01 L_\mathrm{Edd}/c^2$ and 10 LEdd/c2. In the initially radiation-pressure-dominated disk, we confirm the presence of global inertial-acoustic oscillations of frequency slightly above the maximum radial epicyclic one. In the gas-pressure-dominated Schwarzschild-metric models, we find a velocity oscillation occurring at the maximum value of the radial epicyclic frequency, $3.5\times 10^{-3}\, t_\mathrm{g}^{-1}$, which is most likely a trapped fundamental g-mode. For the Kerr-metric, gas-pressure-dominated disk with dimensionless black hole spin parameter a* = 0.5, the mode frequency is well below the epicyclic frequency maximum, thus confirming that this oscillation is a trapped g-mode. Additionally, the total pressure fluctuations in the disks strongly suggest standing-wave p-modes with frequencies below the apparent g-mode frequency, some trapped in the inner disk close to the ISCO, others present in the middle/outer parts of the disk. The strongest oscillations occur at the breathing oscillation frequency, and are present in all the numerical models we report here, as are weaker velocity oscillations at the vertical epicyclic frequencies. The vertical oscillations show a 3:2 frequency ratio with oscillations occurring approximately at the radial epicyclic frequency, which could be of astrophysical importance in systems with observed twin peak, high-frequency quasi-periodic oscillations.

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Radial modes of levitating atmospheres around Eddington luminosity neutron stars

Cited by 6 publications

References 34 publications

Breathing oscillations in a global simulation of a thin accretion disc

Breathing oscillations in a global simulation of a thin accretion disc

Atmospheric oscillations provide simultaneous measurement of neutron star mass and radius

Relativistic, axisymmetric, viscous, radiation hydrodynamic simulations of geometrically thin discs. II. Disc variability

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