Slim Accretion Disks: Theory and Observational Consequences

Czerny, Bozena

doi:10.3390/universe5050131

Cited by 26 publications

(14 citation statements)

References 75 publications

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“…This model has frequently been applied to explain short-time spectral changes in type 1 Seyfert galaxies by changes in the location and geometry of the corona. Third, on longer timescales, changes in the accretion rate including disk instabilities can cause high or low states in AGN (e.g., Ross et al 2018;Czerny 2019). This last mechanism has been favored to explain some of the extreme changinglook AGN that also switch their Seyfert types.…”

Section: Discussionmentioning

confidence: 99%

Lifting the curtain: The Seyfert galaxy Mrk 335 emerges from deep low-state in a sequence of rapid flare events

Komossa

Grupe

Gallo

et al. 2020

A&A

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Context. The narrow-line Seyfert 1 galaxy Mrk 335 was one of the X-ray brightest active galactic nuclei, but it has systematically faded since 2007. Aims. We report the discovery with Swift of a sequence of bright and rapid X-ray flare events that reveal the emergence of Mrk 335 from its ultra-deep multiyear low state. Methods. Results are based on our dedicated multiyear monitoring of Mrk 335 with Swift. Results. Unlike other bright active galactic nuclei, the optical–UV is generally not correlated with the X-rays in Mrk 335 on a timescale of days to months. This fact either implies the absence of a direct link between the two emission components; or else implies that the observed X-rays are significantly affected by (dust-free) absorption along our line of sight. The UV and optical, however, are closely correlated at the 99.99% confidence level. The UV is leading the optical by Δt = 1.5 ± 1.5 d. The Swift X-ray spectrum shows strong deviations from a single power law in all brightness states of the outbursts, indicating that significant absorption or reprocessing is taking place. Mrk 335 displays a softer-when-brighter variability pattern at intermediate X-ray count rates, which has been seen in our Swift data since 2007 (based on a total of 590 observations). This pattern breaks down at the highest and lowest count rates. Conclusions. We interpret the 2020 brightening of Mrk 335 as a decrease in column density and covering factor of a partial-covering absorber along our line of sight in the form of a clumpy accretion-disk wind that reveals an increasing portion of the intrinsic emission of Mrk 335 from the disk and/or corona region, while the optical emission-line regions receive a less variable spectral energy distribution. This then also explains why Mrk 335 was never seen to change its optical Seyfert type (not “changing look”) despite its factor ∼50 X-ray variability with Swift.

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Section: Discussionmentioning

confidence: 99%

Lifting the curtain: The Seyfert galaxy Mrk 335 emerges from deep low-state in a sequence of rapid flare events

Komossa

Grupe

Gallo

et al. 2020

A&A

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“…In the simplest theoretical framework, active galactic nuclei (AGN) are sources in which a supermassive black hole is surrounded by a geometrically thin, optically thick accretion disk Shakura & Sunyaev (1973). For some objects, though, modifications to accretion disk, like advection-dominated accretion flow (ADAF) or slim accretion disks (for review see Czerny 2019), are needed to better represent the observed spectra. AGN also show variability in different timescale, pattern and wavelengths like X-ray (Lawrence & Papadakis 1993), optical (Sesar et al 2007), and infrared (Kozłowski et al 2016) bands.…”

Section: Introductionmentioning

confidence: 99%

Modeling changing‐look active galactic nuclei phenomenon in 1D using accretion disk instabilities

2021

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Apart from regular, low-level stochastic variability, some active galactic nuclei (AGN) occasionally show exceptionally large changes in the luminosity, spectral shape, and/or X-ray absorption. The most notable are the changes of the spectral type when the source classified as a Seyfert 1 becomes a Seyfert 2 galaxy or vice versa. Thus, a name was coined of "changing-look AGN" (CL AGN). The origin of this phenomenon is still unknown, but for most of the sources, there are strong arguments in favor of the intrinsic changes. Understanding the nature of such rapid changes is a challenge to the models of black hole accretion flows since the timescales of the changes are much shorter than the standard disk viscous timescales. We aim to model the CL AGN phenomenon assuming that the underlying mechanism is the time-dependent evolution of a black hole accretion disk unstable due to the dominant radiation pressure. We use a one-dimensional, vertically integrated disk model, but we allow for the presence of the hot coronal layer above the disk and the presence of the inner purely hot flow. We focus on the variability timescales and amplitudes, which can be regulated by the action of large-scale magnetic fields, the description of the disk-corona coupling and the presence of an inner optically thin flow, like advection-dominated accretion flow. We compare model predictions for the accretion disk around black hole mass 10 7 M ⊙ .

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“…However, due to their extremely large optical depths, accretion disks with Ṁ ṀEdd can no longer cool efficiently. The accretion flow traps photons and the advection of radiation becomes the primary mode of energy transport in the disk (Begelman 1978;Abramowicz et al 1988;Sadowski & Narayan 2016;Czerny 2019). The large concentration of photons launches a radiation-pressuredriven outflow, which originates at the radius where the radiation flux through the surface of the disk becomes super-Eddington (Shakura & Sunyaev 1973).…”

Section: Introductionmentioning

confidence: 99%

Beamed emission from a neutron-star ULX in a GRRMHD simulation

Abarca,

Parfrey,

Kluźniak

2021

Preprint

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We perform a global 2.5D general-relativistic radiation magnetohydrodynamic simulation of supercritical accretion onto a neutron star with a 2 × 10 10 G dipolar magnetic field, as a model of a neutronstar-powered ultraluminous X-ray source (ULX). We compute a lower limit on the total luminosity of ∼ 2.5 L Edd , and find the radiation to be highly beamed by the accretion disk outflows. The apparent isotropic luminosity, which is a function of the viewing angle, reaches a maximum above 100 L Edd , consistent with the luminosities observed in ULXs.

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Slim Accretion Disks: Theory and Observational Consequences

Cited by 26 publications

References 75 publications

Lifting the curtain: The Seyfert galaxy Mrk 335 emerges from deep low-state in a sequence of rapid flare events

Lifting the curtain: The Seyfert galaxy Mrk 335 emerges from deep low-state in a sequence of rapid flare events

Modeling changing‐look active galactic nuclei phenomenon in 1D using accretion disk instabilities

Beamed emission from a neutron-star ULX in a GRRMHD simulation

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