X-ray ionized reflection occurs when a surface is irradiated with X-rays so intense that its ionization state is determined by the ionization parameter ξ ∝ F/n, where F is the incident flux and n the gas density. It occurs in accretion, on to compact objects including black holes in both active galaxies and stellar-mass binaries, and possibly in gamma-ray bursts. Computation of model reflection spectra is often time consuming. Here we present the results from a comprehensive grid of models computed with our code, which has now been extended to include what we consider to be all energetically important ionization states and transitions. This grid is being made available as an ionized-reflection model, REFLION, for XSPEC. Ke yw ords: accretion, accretion discs ‐ line: formation ‐ radiative transfer ‐ galaxies: active ‐ X-rays: general.

/pdf/a-comprehensive-range-of-x-ray-ionized-reflection-models-536yauzu5h.pdf

A comprehensive range of X-ray ionized-reflection models

We present a new and complete library of synthetic spectra for modeling the component of emission that is reflected from an illuminated accretion disk. The spectra were computed using an updated version of our code xillver that incorporates new routines and a richer atomic data base. We offer in the form of a table model an extensive grid of reflection models that cover a wide range of parameters. Each individual model is characterized by the photon index Gamma of the illuminating radiation, the ionization parameter zeta at the surface of the disk (i.e., the ratio of the X-ray flux to the gas density), and the iron abundance A(sub Fe) relative to the solar value. The ranges of the parameters covered are: 1.2 <= Gamma <= 3.4, 1 <= zeta <= 104, and 0.5 <= A(sub Fe) <= 10. These ranges capture the physical conditions typically inferred from observations of active galactic nuclei, and also stellar-mass black holes in the hard state. This library is intended for use when the thermal disk flux is faint compared to the incident power-law flux. The models are expected to provide an accurate description of the Fe K emission line, which is the crucial spectral feature used to measure black hole spin. A total of 720 reflection spectra are provided in a single FITS file suitable for the analysis of X-ray observations via the atable model in xspec. Detailed comparisons with previous reflection models illustrate the improvements incorporated in this version of xillver.

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X-ray reflected spectra from accretion disk models. iii. a complete grid of ionized reflection calculations

We present new models for illuminated accretion disks, their structure, and reprocessed emission. We consider the effects of incident X-rays on the surface of an accretion disk by simultaneously solving the equations of radiative transfer, energy balance, and ionization equilibrium over a large range of column densities. We assume plane-parallel geometry and azimuthal symmetry, such that each calculation corresponds to a ring at a given distance from the central object. Our models include recent and complete atomic data for K-shell processes of the iron and oxygen isonuclear sequences. We examine the effect on the spectrum of fluorescent Kα line emission and absorption in the emitted spectrum. We also explore the dependence of the spectrum on the strength of the incident X-rays and other input parameters, and discuss the importance of Comptonization on the emitted spectrum.

/pdf/x-ray-reflected-spectra-from-accretion-disk-models-i-3c9ec5s5at.pdf

X-ray reflected spectra from accretion disk models. I. Constant density atmospheres

We present a new and complete library of synthetic spectra for modeling the component of emission that is reflected from an illuminated accretion disk The spectra were computed using an updated version of our code XILLVER that incorporates new routines and a richer atomic data base We offer in the form of a table model an extensive grid of reflection models that cover a wide range of parameters Each individual model is characterized by the photon index \Gamma of the illuminating radiation, the ionization parameter \xi at the surface of the disk (ie, the ratio of the X-ray flux to the gas density), and the iron abundance A_{Fe} relative to the solar value The ranges of the parameters covered are: 12 \leq \Gamma \leq 34, 1 \leq \xi \leq 10^4, and 05 \leq A_{Fe} \leq 10 These ranges capture the physical conditions typically inferred from observations of active galactic nuclei, and also stellar-mass black holes in the hard state This library is intended for use when the thermal disk flux is faint compared to the incident power-law flux The models are expected to provide an accurate description of the Fe K emission line, which is the crucial spectral feature used to measure black hole spin A total of 720 reflection spectra are provided in a single FITS file{\url{this http URL}} suitable for the analysis of X-ray observations via the atable model in XSPEC Detailed comparisons with previous reflection models illustrate the improvements incorporated in this version of XILLVER

X-ray reflected spectra from accretion disk models. III. A complete grid of ionized reflection calculations

Accreting black holes are believed to emit X-rays, which then mediate information about strong gravity in the vicinity of the emission region. We report on a set of new routines for the XSPEC package for analyzing X-ray spectra of black-hole accretion disks. The new computational tool significantly extends the capabilities of the currently available fitting procedures that include the effects of strong gravity and allows one to systematically explore the constraints on more model parameters than previously possible (e.g., black-hole angular momentum). Moreover, axial symmetry of the disk intrinsic emissivity is not assumed, although it can be imposed to speed up the computations. The new routines can be used also as a stand-alone and flexible code with the capability of handling time-resolved spectra in the regime of strong gravity. We have used the new code to analyze the mean X-ray spectrum from the long XMM-Newton 2001 campaign of the Seyfert 1 galaxy MCG -6-30-15. Consistent with previous findings, we obtained a good fit to the broad Fe K line profile for a radial line intrinsic emissivity law in the disk that is not a simple power law, and for near maximal value of black hole angular momentum. However, equally good fits can be obtained also for small values of the black hole angular momentum. The code has been developed with the aim of allowing precise modeling of relativistic effects. Although we find that current data cannot constrain the parameters of black-hole/accretion disk system well, the code allows, for a given source or situation, detailed investigations of what features of the data future studies should be focused on in order to achieve the goal of uniquely isolating the parameters of such systems.

https://iopscience.iop.org/article/10.1086/421115/pdf

An Extended Scheme for Fitting X-Ray Data with Accretion Disk Spectra in the Strong Gravity Regime

We present detailed computations of the vertical structure of an accretion disc illuminated by hard X-ray radiation with the code titan-noar, which is suitable for Compton-thick media. The energy generated via accretion is dissipated partially in the cold disc as well as in the X-ray source. We study the differences between the case where the X-ray source is in the form of a lamp-post above the accretion disc and the case of a heavy corona. We consider radiative heating via Comptonization together with heating via photo-absorption on numerous heavy elements such as carbon, oxygen, silicon and iron. The transfer in lines is precisely calculated. A better description of the heating/cooling through the inclusion of line transfer, a correct description of the temperature in the deeper layers, and a correct description of the entire disc vertical structure, as well as the study of the possible coronal pressure effect, constitute an improvement in comparison to previous works.



We show that exact calculations of hydrostatic equilibrium and determination of the disc thickness have a crucial impact on the optical depth of the hot illuminated zone. We study the lamp-post model for a low (m˙=0.03) and high (m˙=0.3) accretion rate. In both cases we assume a moderate illumination where the viscous flux equals the X-ray radiation flux. A highly ionized skin is created in the lamp-post model, with the outgoing spectrum containing many emission lines and ionization edges in emission or absorption in the soft X-ray domain, as well as an iron line at ∼7 keV consisting of a blend of a low-ionization line from the deepest layers and hydrogen- and helium-like resonance lines from the upper layers, and almost no absorption edge, contrary to the case of a slab of constant density. A full heavy corona completely suppresses the highly ionized zone on the top of the accretion disc and in such a case the spectrum is featureless.

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The structure and radiation spectra of illuminated accretion discs in active galactic nuclei – I. Moderate illumination

We present a model of the vertical stratication and the spectra of an irradiated medium under the assumption of constant pressure Such a solution has properties intermediate between constant density models and hydrostatic equilibrium models, and it may represent a flattened conguration of gas clumps accreting onto the central black hole Such a medium develops a hot skin, thicker than hydrostatic models, but thinner than constant density models, under comparable irradiation The range of theoretical values of the ox index is comparable to those from hydrostatic models and both are close to the observed values for Seyfert galaxies but lower than in quasars The amount of X-ray Compton reflection is consistent with the observed range The characteristic property of the model is a frequently multicomponent iron K line

/pdf/reprocessing-of-x-rays-in-agn-i-plane-parallel-geometry-test-4yb4chumtt.pdf

S. Collin

Papers

The structure and radiation spectra of illuminated accretion discs in active galactic nuclei – I. Moderate illumination

Reprocessing of x-rays in agn. I. plane parallel geometry - test of pressure equilibrium