Thermal instability in X-ray photoionized media in active  galactic nuclei

Chevallier, L.; Gonçalves, A. C.; Różáńska, A.; Dumont, A. M.

doi:10.1051/0004-6361/200810956

Cited by 8 publications

(6 citation statements)

References 30 publications

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“…Neither titan nor cloudy have this option. However, the position of the discontinuity is well determined on the basis of radiative transfer only, as was shown by Czerny et al (2009) and its extension depends on the model parameters.…”

Section: Comparison With Observationsmentioning

confidence: 99%

ABSORPTION MEASURE DISTRIBUTION IN Mrk 509

Adhikari

Różáńska

Sobolewska

2015

ApJ

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In this paper we model the observed absorption measure distribution (AMD) in Mrk 509, which spans three orders of magnitude in ionization level with a single-zone absorber in pressure equilibrium. AMD is usually constructed from observations of narrow absorption lines in radio-quiet active galaxies with warm absorbers. We study the properties of the warm absorber in Mrk 509 using recently published broad-band spectral energy distribution observed with different instruments. This spectrum is an input in radiative transfer computations with full photoionisation treatment using titan code. We show that the simplest way to fully reproduce the shape of AMD is to assume that the warm absorber is a single zone under constant total pressure. With this assumption we found theoretical AMD which matches the observed one determined on the basis of 600 ks RGS XMM-Newton spectrum of Mrk 509. The softness of the source spectrum and the important role of the free-free emission breaks the usual degeneracy in the ionization state calculations, and the explicit dependence of the depths of AMD dips on density open a new path to density diagnostic for the warm absorber. In Mrk 509 the implied density is of the order of 10 8 cm −3 .

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Section: Comparison With Observationsmentioning

confidence: 99%

ABSORPTION MEASURE DISTRIBUTION IN Mrk 509

Adhikari

Różáńska

Sobolewska

2015

ApJ

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“…10 and Fig. 17, the column density of a group of clumps ranges from a few ×10 22 cm −2 to a few ×10 23 cm −2 and the column density for a particular light-of-sight show a rapid time variation with timescales of ≈ 10 2 -3 yr. A possible mechanism for the formation of clumpy structures may be coupled with thermal instability (e.g., Krolik et al 1981;Różańska 1999;Gonçalves et al 2007;Czerny et al 2009;Proga & Waters 2015), i.e., a transition from cold phase (T gas ≈ 10 2 -3 K) to hot phase (T gas ≈ (1 -3) × 10 4 K), and the subsequent ejection of hot phase gas. The comparison between the high resolution model and the low resolution one suggests that the spatial resolution is important for such transition to occur.…”

Section: The Effects Of Spatial Resolutionmentioning

confidence: 99%

Sub-parsec-scale dynamics of a dusty gas disc exposed to anisotropic AGN radiation with frequency-dependent radiative transfer

Namekata

Umemura

2016

Mon. Not. R. Astron. Soc.

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We explore the gas dynamics near the dust sublimation radius of active galactic nucleus (AGN). For the purpose, we perform axisymmetric radiation hydrodynamic simulations of a dusty gas disk of radius ≈ 1 pc around a supermassive black hole of mass 10 7 M taking into account (1) anisotropic radiation of accretion disk, (2) X-ray heating by corona, (3) radiative transfer of infrared (IR) photons reemitted by dust, (4) frequency dependency of direct and IR radiations, and (5) separate temperatures for gas and dust. As a result, we find that for Eddington ratio ≈ 0.77, a nearly neutral, dense (≈ 10 6 -8 cm −3 ), geometrically-thin (h/r < 0.06) disk forms with a high velocity (≈ 200 ∼ 3000 km s −1 ) dusty outflow launched from the disk surface. The disk temperature is determined by the balance between X-ray heating and various cooling, and the disk is almost supported by thermal pressure. Contrary to Krolik (2007), the radiation pressure by IR photons is not effective to thicken the disk, but rather compresses it. Thus, it seems difficult for a radiation-supported, geometrically-thick, obscuring torus to form near the dust sublimation radius as far as the Eddington ratio is high (∼ 1). The mass outflow rate is 0.05 -0.1 M /yr and the column density of the outflow is N H 10 21 cm −2 . To explain observed type-II AGN fraction, it is required that outflow gas is extended to larger radii (r 10 pc) or that a denser dusty wind is launched from smaller radii (r ∼ 10 4 R g ).

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“…Krolik & Kriss 2001;Steenbrugge et al 2005). The most complete warm absorber models, which include RPC, are presented by Różańska et al (2006) (see also Gonçalves et al 2007;Czerny et al 2009). Their model (titan) allows to derive the two stable solutions at a given pressure.…”

Section: Numerical Solutionsmentioning

confidence: 99%

Radiation pressure confinement – II. Application to the broad-line region in active galactic nuclei

Baskin¹,

Laor²,

Stern³

2013

Monthly Notices of the Royal Astronomical Society

116

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Active galactic nuclei (AGN) are characterized by similar broad emission lines properties at all luminosities (10 39 -10 47 erg s −1 ). What produces this similarity over a vast range of 10 8 in luminosity? Photoionization is inevitably associated with momentum transfer to the photoionized gas. Yet, most of the photoionized gas in the Broad Line Region (BLR) follows Keplerian orbits, which suggests that the BLR originates from gas with a large enough column for gravity to dominate. The photoionized surface layer of the gas must develop a pressure gradient due to the incident radiation force. We present solutions for the structure of such a hydrostatic photoionized gas layer in the BLR. The gas is stratified, with a low-density highly-ionized surface layer, a density rise inwards, and a uniform-density cooler inner region, where the gas pressure reaches the incident radiation pressure. This radiation pressure confinement (RPC) of the photoionized layer leads to a universal ionization parameter U ∼ 0.1 in the inner photoionized layer, independent of luminosity and distance. Thus, RPC appears to explain the universality of the BLR properties in AGN. We present predictions for the BLR emission per unit covering factor, as a function of distance from the ionizing source, for a range of ionizing continuum slopes and gas metallicity. The predicted mean strength of most lines (excluding H β), and their different average-emission radii, are consistent with the available observations.

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Thermal instability in X-ray photoionized media in active galactic nuclei

Cited by 8 publications

References 30 publications

ABSORPTION MEASURE DISTRIBUTION IN Mrk 509

ABSORPTION MEASURE DISTRIBUTION IN Mrk 509

Sub-parsec-scale dynamics of a dusty gas disc exposed to anisotropic AGN radiation with frequency-dependent radiative transfer

Radiation pressure confinement – II. Application to the broad-line region in active galactic nuclei

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