Local Stability and Global Instability in Iron-opaque Disks

Grzȩdzielski, Mikołaj; Janiuk, Agnieszka

doi:10.3847/1538-4357/aa7dd9

Cited by 7 publications

(9 citation statements)

References 24 publications

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“…Second, the opacity drives convection that isn't present in the previous simulations, which enhances the nonradiative fluxes carried in the simulations. However, the dependence of shearing box simulations on box size, combined with timedependent global modeling (Grzȩdzielski, Janiuk & Czerny 2017) strongly motivates further study of UV opacity effects in global numerical simulations.…”

Section: Thermal Instability In Radiation Pressure Dominated Accretionmentioning

confidence: 99%

Magnetohydrodynamics Simulations of Active Galactic Nucleus Disks and Jets

Davis

Tchekhovskoy

2020

Annu. Rev. Astron. Astrophys.

116

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There is a broad consensus that accretion onto supermassive black holes and consequent jet formation power the observed emission from active galactic nuclei (AGNs). However, there has been less agreement about how jets form in accretion flows, their possible relationship to black hole spin, and how they interact with the surrounding medium. There have also been theoretical concerns about instabilities in standard accretion disk models and lingering discrepancies with observational constraints. Despite seemingly successful applications to X-ray binaries, the standard accretion disk model faces a growing list of observational constraints that challenge its application to AGNs. Theoretical exploration of these questions has become increasingly reliant on numerical simulations owing to the dynamic nature of these flows and the complex interplay between hydrodynamics, magnetic fields, radiation transfer, and curved spacetime. We conclude the following: ▪ The advent of general relativistic magnetohydrodynamics (MHD) simulations has greatly improved our understanding of jet production and its dependence on black hole spin. ▪ Simulation results show both disks and jets are sensitive to the magnetic flux threading the accretion flow as well as possible misalignment between the angular momentum of the accretion flow and the black hole spin. ▪ Radiation MHD simulations are providing new insights into the stability of luminous accretion flows and highlighting the potential importance of radiation viscosity, UV opacity from atoms, and spiral density waves in AGNs. Expected final online publication date for the Annual Review of Astronomy, Volume 58 is August 18, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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Section: Thermal Instability In Radiation Pressure Dominated Accretionmentioning

confidence: 99%

Magnetohydrodynamics Simulations of Active Galactic Nucleus Disks and Jets

Davis

Tchekhovskoy

2020

Annu. Rev. Astron. Astrophys.

116

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“…We compute the opacity value self-consistently with the density and temperature at each radius with an iterative process, using as reference stellar opacity tables (at solar metallicity) from the Opacity Project (Seaton et al 1994;Seaton 1995). This is important since the density and temperature regimes relevant for AGN disks imply opacities that can be significantly different from the electron scattering value (e.g., see Jiang et al 2016;Czerny et al 2016;Grzȩdzielski et al 2017a). Further, we assume a downward component of the X-ray emission (η) and a disk albedo (a disk ), which modify the disk equations from the usual (1 − f ) factor (M03; Svensson & Zdziarski 1994) to:…”

Section: The Disk-corona Modelmentioning

confidence: 99%

Testing the disk-corona interplay in radiatively-efficient broad-line AGN

Arcodia

Merloni

Nandra

et al. 2019

A&A

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The correlation observed between monochromatic X-ray and UV luminosities in radiatively-efficient active galactic nuclei (AGN) lacks a clear theoretical explanation despite being used for many applications. Such a correlation, with its small intrinsic scatter and its slope that is smaller than unity in log space, represents the compelling evidence that a mechanism regulating the energetic interaction between the accretion disk and the X-ray corona must be in place. This ensures that going from fainter to brighter sources the coronal emission increases less than the disk emission. We discuss here a self-consistently coupled disk-corona model that can identify this regulating mechanism in terms of modified viscosity prescriptions in the accretion disk. The model predicts a lower fraction of accretion power dissipated in the corona for higher accretion states. We then present a quantitative observational test of the model using a reference sample of broad-line AGN and modeling the disk-corona emission for each source in the L X − L UV plane. We used the slope, normalization, and scatter of the observed relation to constrain the parameters of the theoretical model. For non-spinning black holes and static coronae, we find that the accretion prescriptions that match the observed slope of the L X − L UV relation produce X-rays that are too weak with respect to the normalization of the observed relation. Instead, considering moderatelyoutflowing Comptonizing coronae and/or a more realistic high-spinning black hole population significantly relax the tension between the strength of the observed and modeled X-ray emission, while also predicting very low intrinsic scatter in the L X − L UV relation. In particular, this latter scenario traces a known selection effect of flux-limited samples that preferentially select high-spinning, hence brighter, sources.

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“…Our global simulations, with a range of µ-paramater values for the stress tensor, have shown that the limit cycle oscillations appear. They are suffering some disturbances from the Iron Opacity Bump, but nevertheless are still expected in AGN over a wide range of black hole mass [19].…”

Section: Modified Stress Tensormentioning

confidence: 99%