Ionization Instability Driven Outbursts in SXTs

Bagińska, Patrycja; Różáńska, A.; Janiuk, Agnieszka

doi:10.3847/1538-4357/abee79

Cited by 7 publications

(4 citation statements)

References 71 publications

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“…Most known black hole X-ray binaries (BHXBs) undergo a cycle of outbursts, driven by a mass accretion rate modulation caused by an outer disk instability (Homan et al 2001;Lasota 2001;Bagińska et al 2021). During outburst, in a luminous (0.05 < 𝐿/𝐿 Edd < 0.3) soft (thermal) spectral state, the observations are consistent with multiblackbody spectra expected from the classic analytic thin 𝛼-disk model in its relativistic version (NT disk;Novikov & Thorne 1973;Clintock et al 2006), as the disk geometry begins to deviate from the geometrical thinness assumption.…”

Section: Introductionmentioning

confidence: 99%

Observational properties of puffy disks: radiative GRMHD spectra of mildly sub-Eddington accretion

Wielgus,

Lancova,

Straub

et al. 2022

Preprint

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Numerical general relativistic radiative magnetohydrodynamic simulations of accretion disks around a stellar mass black hole with a luminosity above 0.5 of the Eddington value reveal their stratified, elevated vertical structure. We refer to these thermally stable numerical solutions as puffy disks. Above a dense and geometrically thin core of dimensionless thickness ℎ/𝑟 ∼ 0.1, crudely resembling a classic thin accretion disk, a puffed-up, geometrically thick layer of lower density and ℎ/𝑟 ∼ 1.0 is formed. We discuss the observational properties of puffy disks, in particular the geometrical obscuration of the inner disk by the elevated puffy region at higher observing inclinations, and collimation of the radiation along the accretion disk spin axis, which may explain the apparent super-Eddington luminosity of some X-ray objects. We also present synthetic spectra of puffy disks, and show that they are qualitatively similar to those of a Comptonized thin disk. We demonstrate that the existing spectral fitting models provide good fits to synthetic observations of puffy disks, but cannot correctly recover the input black hole spin. The puffy region remains optically thick to scattering; in its spectral properties the puffy disk roughly resembles that of a warm corona sandwiching the disk core. We suggest that puffy disks may correspond to X-ray binary systems of luminosities above 0.3 of the Eddington luminosity in the intermediate spectral states.

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Section: Introductionmentioning

confidence: 99%

Observational properties of puffy disks: radiative GRMHD spectra of mildly sub-Eddington accretion

Wielgus,

Lancova,

Straub

et al. 2022

Preprint

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“…However, FRED light curves are rather exceptional cases. Observed irregularities, platoes, breaks, and reflares of the light curves demonstrate physical complexity calling for further analytic and numerical considerations (see, e.g., Bagińska et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Physical modeling of viscous disc evolution around magnetized neutron star. Aql X-1 2013 outburst decay

Lipunova,

Malanchev,

Tsygankov

et al. 2021

Preprint

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We present a model of a viscously evolving accretion disc around a magnetized neutron star. The model features the varying outer radius of the hot ionized part of the disc due to cooling and the varying inner radius of the disc due to interaction with the magnetosphere. It also includes hindering of accretion on the neutron star because of the centrifugal barrier and irradiation of the outer disc and companion star by X-rays from the neutron star and disc. When setting inner boundary conditions, we take into account that processes at the inner disc occur on a time scale much less than the viscous time scale of the whole disc. We consider three types of outflow from the disc inner edge: zero outflow, one based on MHD calculations, and a very efficient propeller mechanism. The light curves of an X-ray transient after the outburst peak can be calculated by a corresponding, publicly available code. We compare observed light curves of the 2013 burst of Aql X-1 in X-ray and optical bands with modeled ones. We find that the fast drop of the 0.3 − 10 keV flux can be solely explained by a radial shrinking of the hot disc. At the same time, models with the neutron star magnetic field > 10 8 G have better fits because the accretion efficiency behaviour emphasizes the 'knee' on the light curve. We also find that a plato emission can be produced by a disc-reservoir with stalled accretion.

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“…A model based on the instability has been developed in a number of works (e.g., Hōshi (1979); Smak (1982a); Meyer & Meyer-Hofmeister (1981; Faulkner et al (1983); Papaloizou et al (1983); Smak (1984)). Presently, it is referred to as the Disc Instability Model (or DIM, Hameury et al 1998;Lasota 2001;Hameury 2020), see also Bagińska et al (2021). Details of DIM depend not only on the disc vertical structure at different radii but on the radial energy transport as well.…”

Section: Introductionmentioning

confidence: 99%

Vertical structure and stability of accretion discs with convective energy transport and external X-ray irradiation

Tavleev¹,

Lipunova²,

Malanchev³

2023

Preprint

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Radial structure of accretion discs around compact objects is often described using analytic approximations which are derived from averaging or integrating vertical structure equations. For non-solar chemical composition, partial ionization, or for supermassive black holes, this approach is not accurate. Additionally, radial extension of 'analytically-described' disc zones is not evident in many cases. We calculate vertical structure of accretion discs around compact objects, with and without external irradiation, with radiative and convective energy transport taken into account. For this, we introduce a new open Python code, allowing different equations of state (EoS) and opacity laws, including tabular values. As a result, radial structure and stability 'S-curves' are calculated for specific disc parameters and chemical composition. In particular, based on more accurate power-law approximations for opacity in the disc, we supply new analytic formulas for the farthest regions of the hot disc around stellar-mass object. On calculating vertical structure of a self-irradiated disc, we calculate a self-consistent value of the irradiation parameter 𝐶 irr for stationary 𝛼-disc. We find that, for a fixed shape of the X-ray spectrum, 𝐶 irr depends weakly on the accretion rate but changes with radius, and the dependence is driven by the conditions in the photosphere and disc opening angle. The hot zone extent depends on the ratio between irradiating and intrinsic flux: corresponding relation for 𝑇 irr, crit is obtained.

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Ionization Instability Driven Outbursts in SXTs

Cited by 7 publications

References 71 publications

Observational properties of puffy disks: radiative GRMHD spectra of mildly sub-Eddington accretion

Observational properties of puffy disks: radiative GRMHD spectra of mildly sub-Eddington accretion

Physical modeling of viscous disc evolution around magnetized neutron star. Aql X-1 2013 outburst decay

Vertical structure and stability of accretion discs with convective energy transport and external X-ray irradiation

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