scholarly journals Sustaining a warm corona in active galactic nucleus accretion discs

2020 ◽  
Vol 496 (4) ◽  
pp. 4255-4265
Author(s):  
D R Ballantyne ◽  
X Xiang
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Coronal Heating ◽  
Accretion Discs ◽  
Constant Density ◽  
One Dimensional ◽  
X Ray ◽  
Average Lead

ABSTRACT Warm coronae, thick (τT = 10–20, where τT is the Thomson depth) Comptonizing regions with temperatures of ∼1 keV, are proposed to exist at the surfaces of accretion discs in active galactic nuclei (AGNs). By combining with the reflection spectrum, warm coronae may be responsible for producing the smooth soft excess seen in AGN X-ray spectra. This paper studies how a warm corona must adjust in order to sustain the soft excess through large changes in the AGN flux. Spectra from one-dimensional constant density and hydrostatic warm corona models are calculated assuming that the illuminating hard X-ray power law, gas density, Thomson depth, and coronal heating strength vary in response to changes in the accretion rate. We identify models that produce warm coronae with temperatures between 0.3 and 1.1 keV, and measure the photon indices and emitted fluxes in the 0.5–2 and 2–10 keV bands. Correlations and anticorrelations between these quantities depend on the evolution and structure of the warm corona. Tracing the path that an AGN follows through these correlations will constrain how warm coronae are heated and connected to the accretion disc. Variations in the density structure and coronal heating strength of warm coronae will lead to a variety of soft excess strengths and shapes in AGNs. A larger accretion rate will, on average, lead to a warm corona that produces a stronger soft excess, consistent with observations of local Seyfert galaxies.

scholarly journals Cosmological Evolution of the Central Engine in High-Luminosity, High-Accretion Rate AGN

2014 ◽  
Vol 1 (1) ◽  
pp. 90-95
Author(s):  
Matteo Guainazzi
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Cosmological Evolution ◽  
High Luminosity ◽  
X Ray ◽  
Central Engine ◽  
The Status ◽  
Multi Wavelength

In this paper I discuss the status of observational studies aiming at probing the cosmological evolution of the central engine in high-luminosity, high-accretion rate Active Galactic Nuclei (AGN). X-ray spectroscopic surveys, supported by extensive multi-wavelength coverage, indicate a remarkable invariance of the accretion disk plus corona system, and of their coupling up to redshifts z≈6. Furthermore, hard X-ray (<em>E</em> &gt;10 keV) surveys show that nearby Seyfert Galaxies share the same central engine notwithstanding their optical classication. These results suggest that the high-luminosity, high accretion rate quasar phase of AGN evolution is homogeneous over cosmological times.

scholarly journals Examining the physical conditions of a warm corona in active galactic nuclei accretion discs

2019 ◽  
Vol 491 (3) ◽  
pp. 3553-3561 ◽  
Author(s):  
D R Ballantyne
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Accretion Discs ◽  
Internal Heating ◽  
One Dimensional ◽  
X Ray ◽  
Physical Conditions ◽  
Gas Layer ◽  
Hot Corona

ABSTRACT A warm corona at the surface of an accretion disc has been proposed as a potential location for producing the soft excess commonly observed in the X-ray spectra of active galactic nuclei (AGNs). In order to fit the observed data, the gas must be at temperatures of ∼1 keV and have an optical depth of τT ≈ 10–20. We present one-dimensional calculations of the physical conditions and emitted spectra of a τT = 10 or 20 gas layer subject to illumination from an X-ray power law (from above), a blackbody (from below), and a variable amount of internal heating. The models show that a warm corona with kT ∼ 1 keV can develop, producing a strong Comptonized soft excess, but only if the internal heating flux is within a relatively narrow range. Similarly, if the gas density of the layer is too large then efficient cooling will stop a warm corona from forming. The radiation from the hard X-ray power law is crucial in producing a warm corona, indicating that a warm and hot corona may coexist in AGN accretion discs, and their combined effect leads to the observed soft excess. Intense heating of a warm corona leads to steep X-ray spectra with ionized Fe K α lines, similar to those seen in some narrow-line Seyfert 1 galaxies.

scholarly journals The Jet-Disk Coupling of Seyfert Galaxies from a Complete Hard X-ray Sample

Universe ◽  
2020 ◽  
Vol 6 (5) ◽  
pp. 68 ◽  
Author(s):  
Xiang Liu ◽  
Ning Chang ◽  
Zhenhua Han ◽  
Xin Wang
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Radio Galaxies ◽  
Powerful Radio ◽  
Linear Coupling ◽  
X Ray ◽  
Radiative Efficiency ◽  
Coupling Index

We analyze the jet-disk coupling for different subsamples from a complete hard X-ray Seyfert sample to study the coupling indices and their relation to accretion rate. The results are: (1) the power-law coupling index ranges from nearly unity (linear correlation) for radio loud Seyferts to significantly less than unity for radio quiet ones. This decline trend of coupling index also holds from larger sources to compact ones; (2) the Seyferts with intermediate to high accretion rate (Eddington ratio λ ∼ 0.001 to 0.3) show a linear jet-disk coupling, but it shallows from near to super Eddington ( λ ∼ 0.3 to 10), and the former is more radio loud than the latter; (3) the Seyfert 1s are slightly steeper than the Seyfert 2s, in the jet-disk correlation. In the linear coupling regime, the ratio of jet efficiency to radiative efficiency ( η / ε ) is nearly invariant, but in low accretion or super accretion regime, η / ε varies with λ in our model. We note that a radio-active cycle of accretion-dominated active galactic nuclei would be: from a weaker jet-disk coupling in λ < 0 . 001 for low luminosity Seyferts, to a linear coupling in 0 . 001 < λ < 0 . 3 for radio-loud luminous Seyferts and powerful radio galaxies/quasars, and to a weaker coupling in 0 . 3 < λ < 10 ones.

scholarly journals Radiative efficiency of hot accretion flow and the radio/X-ray correlation in X-ray binaries

2014 ◽  
Vol 10 (S312) ◽  
pp. 139-140
Author(s):  
Fu-Guo Xie
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
X Ray ◽  
Radiative Efficiency ◽  
Accretion Flow ◽  
Accretion Rates ◽  
Distinctive Property ◽  
X Ray Binaries

AbstractSignificant progresses have been made since the discovery of hot accretion flow, a theory successfully applied to the low-luminosity active galactic nuclei (LLAGNs) and black hole (BH) X-ray binaries (BHBs) in their hard states. Motivated by these updates, we re-investigate the radiative efficiency of hot accretion flow. We find that, the brightest regime of hot accretion flow shows a distinctive property, i.e. it has a constant efficiency independent of accretion rates, similar to the standard thin disk. For less bright regime, the efficiency has a steep positive correlation with the accretion rate, while for faint regime typical of advection-dominated accretion flow, the correlation is shadower. This result can naturally explain the observed two distinctive correlations between radio and X-ray luminosities in black hole X-ray binaries. The key difference in systems with distinctive correlations could be the viscous parameter, which determines the critical luminosity of different accretion modes.

scholarly journals Line-driven disc wind in near-Eddington active galactic nuclei: decrease of mass accretion rate due to powerful outflow

2020 ◽  
Vol 494 (3) ◽  
pp. 3616-3626 ◽  
Author(s):  
Mariko Nomura ◽  
Ken Ohsuga ◽  
Chris Done
Keyword(s):  
Black Holes ◽  
Mass Loss ◽  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
Host Galaxy ◽  
Radiation Hydrodynamics ◽  
Iterative Technique ◽  
X Ray ◽  
Mass Accretion Rate

ABSTRACT Based on recent X-ray observations, ultrafast outflows from supermassive black holes are expected to have enough energy to dramatically affect their host galaxy but their launch and acceleration mechanisms are not well understood. We perform two-dimensional radiation hydrodynamics simulations of UV line-driven disc winds in order to calculate the mass-loss rates and kinetic power in these models. We develop a new iterative technique that reduces the mass accretion rate through the inner disc in response to the wind mass-loss. This makes the inner disc less UV bright, reducing the wind power compared to previous simulations which assumed a constant accretion rate with radius. The line-driven winds in our simulations are still extremely powerful, with around half the supplied mass accretion rate being ejected in the wind for black holes with mass 108–$10^{10}\, \mathrm{ M}_\odot$ accreting at L/LEdd = 0.5–0.9. Our results open up the way for estimating the growth rate of supermassive black hole and evaluating the kinetic energy ejected into the interstellar medium (active galactic nuclei feedback) based on a physical model of line-driven disc winds.

scholarly journals X-Rays from Active Galactic Nuclei

1983 ◽  
Vol 6 ◽  
pp. 491-498 ◽  
Author(s):  
A.C. Fabian
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
X Rays ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac

Recent X-ray observations of active galactic nuclei and Seyfert galaxies in particular are briefly reviewed. The application of the efficiency limit to rapidly varying luminous sources such as NGC 6814 is discussed. It is argued that the variability and probable MeV spectral turnover imply that most of the electrons which radiate the observed flux are only mildly relativistic. A possible link between the steep soft X-ray spectra and featureless optical continua of BL Lac objects is considered.

scholarly journals On Spin dependence of the Fundamental Plane of black hole activity

2020 ◽  
Vol 495 (1) ◽  
pp. 278-284 ◽  
Author(s):  
Caner Ünal ◽  
Abraham Loeb
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
Spin Dependence ◽  
Fundamental Plane ◽  
X Ray ◽  
Dependent Relation ◽  
Accretion Rates ◽  
Jet Power

ABSTRACT The Fundamental Plane (FP) of black hole (BH) activity in galactic nuclei relates X-ray and radio luminosities to BH mass and accretion rate. However, there is a large scatter exhibited by the data, which motivated us for a new variable. We add BH spin as a new variable and estimate the spin dependence of the jet power and disc luminosity in terms of radio and X-ray luminosities. We assume the Blandford–Znajek process as the main source of the outflow, and find that the jet power depends on BH spin stronger than quadratically at moderate and large spin values. We perform a statistical analysis for 10 active galactic nuclei (AGNs) which have sub-Eddington accretion rates and whose spin values are measured independently via the reflection or continuum-fitting methods, and find that the spin-dependent relation describes the data significantly better. This analysis, if supported with more data, could imply not only the spin dependence of the FP relation, but also the Blandford–Znajek process in AGN jets.

scholarly journals Rapid X-ray variability in active galactic nuclei

1986 ◽  
Vol 119 ◽  
pp. 269-271 ◽  
Author(s):  
P. Barr ◽  
R. Mushotzky ◽  
P. Giommi ◽  
J. Clavel ◽  
W. Wamsteker
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Low Earth Orbit ◽  
Earth Orbit ◽  
Rapid Variability ◽  
X Ray ◽  
Electron Positron ◽  
Eddington Limit

SummaryRecent EXOSAT observations of active galactic nuclei are presented. Unlike earlier X-ray satellites (all of which flew in low earth orbit), the deep orbit of EXOSAT allows long continuous observations of celestial X-ray sources, uninterrupted by earth occultation etc. We present the results of EXOSAT observations of several AGN which have been seen to vary rapidly (timescale 0.2–6 hours). We also consider the implications of rapid variability in AGN. For Seyfert galaxies and quasars, we find a highly significant correlation between the timescale of variability and their X-ray luminosity. They are not, howwever, bounded either by the (classical) Eddington limit nor by efficiency arguments. We sugest, rather, that the emitting plasma is dominated by electron-positron pairs.

scholarly journals X-Ray Properties of Galactic Nuclei

1980 ◽  
Vol 5 ◽  
pp. 623-630
Author(s):  
Daniel W. Weedman
Keyword(s):  
Emission Line ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxy ◽  
Seyfert Galaxies ◽  
Strong Emission ◽  
X Ray ◽  
Ngc 4151 ◽  
Survey Results ◽  
Emission Line Galaxies

Preparing this review was my just punishment for stating only two years ago - in another review (Weedman 1977) - that Seyfert galaxies are not strong X-ray sources. I said that because, as recently as three years ago, NGC 4151 was the only Seyfert galaxy known as an X-ray source. Now we have 36 Seyfert 1 galaxies, along with 12 other galaxies with strong emission-line nuclei, that are X-ray sources. And this is all without even having HEAO-2 data at our disposal yet. The study of active galactic nuclei with X-ray astronomy is progressing so rapidly that a reviewer feels almost hopeless. The best I can do is summarize what is known as of the summer of 1979 and give a simple overview of how X-ray and other properties relate.Some excellent reviews of the X-ray properties of Seyfert and other emission-line galaxies already exist. I especially recommend that by Andrew Wilson (1979). He provides very complete references as of a year ago, but X-ray astronomy is progressing so rapidly that he then had only somewhat more than half the active nuclei now in Tables 1 and 2. It was the group working with the Ariel V SSI that made the initial comprehensive X-ray studies of Seyfert galaxies (Ward et al. 1977, Elvis et al. 1978). The UHURU results for Seyfert galaxies followed soon after and are summarized by Tananbaum et al. (1978); the HEAO-A-2 survey results are now in press (Marshall et al. 1979) I have tried to incorporate these and other recent results in Tables 1 and 2.

scholarly journals Hot Accretion Disks and the High Energy Background

1983 ◽  
Vol 104 ◽  
pp. 345-346
Author(s):  
M. Kafatos ◽  
Jean A. Eilek
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Disks ◽  
Spectral Range ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
High Energy ◽  
X Rays ◽  
X Ray

The origin of the high energy (X-ray and gamma-ray) background may be attributed to discrete sources, which are usually thought to be active galactic nuclei (AGN) (cf. Rothschild et al. 1982, Bignami et al. 1979). At X-rays a lot of information has been obtained with HEAO-1 in the spectral range 2–165 keV. At gamma-rays the background has been estimated from the Apollo 15 and 16 (Trombka et al. 1977) and SAS-2 (Bignami et al. 1979) observations. A summary of some of the observations (Rothschild et al. 1982) is shown in Figure 1. The contribution of AGN to the diffuse high energy background is uncertain at X-rays although it is generally estimated to be in the 20–30% range (Rothschild et al. 1982). At gamma-rays, in the range 1–150 MeV, AGN (specifically Seyfert galaxies) could account for all the emission.

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