Steep X-ray reflection emissivity profiles in AGN as the result of radially structured disc ionization

Kammoun, E. S.; Domček, Vladimír; Svoboda, Jiří; Dovčiak, Michal; Matt, Giorgio

doi:10.1093/mnras/stz408

Cited by 32 publications

(27 citation statements)

References 60 publications

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“…8 (Wilkins & Gallo 2015a). We note that other authors have interpreted very high inner emissivity indices from the fit as a deficiency of the model, in particular of the assumption of a constant ionization profile of the disk (Kammoun et al 2019). Such an interpretation would presumably lead to a different measurement of the spin and of the deformation parameter (Shreeram & Ingram 2020), and we plan to leave the study of such a possibility and its impact in the constraint on α 13 to future work.…”

Section: Impact Of the Disk Thickness On Tests Of The Kerr Black Holementioning

confidence: 92%

Testing the Kerr Black Hole Hypothesis Using X-Ray Reflection Spectroscopy and a Thin Disk Model with Finite Thickness

Abdikamalov

Ayzenberg

Bambi

et al. 2020

ApJ

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X-ray reflection spectroscopy is a powerful tool for probing the strong gravity region of black holes and can be used for testing general relativity in the strong field regime. Simplifications of the available relativistic reflection models limit the capability of performing accurate measurements of the properties of black holes. In this paper, we present an extension of the model relxill nk in which the accretion disk has a finite thickness rather than being infinitesimally thin. We employ the accretion disk geometry proposed by Taylor & Reynolds (2018) and we construct relativistic reflection models for different values of the mass accretion rate of the black hole. We apply the new model to high quality Suzaku data of the X-ray binary GRS 1915+105 to explore the impact of the thickness of the disk on tests of the Kerr metric.

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Section: Impact Of the Disk Thickness On Tests Of The Kerr Black Holementioning

confidence: 92%

Testing the Kerr Black Hole Hypothesis Using X-Ray Reflection Spectroscopy and a Thin Disk Model with Finite Thickness

Abdikamalov

Ayzenberg

Bambi

et al. 2020

ApJ

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“…Given the observed 2-10 keV band luminosity of the X-ray source, the model estimates the intrinsic luminosity and the incident flux on each disk radius, as a function of time (in the observer's frame), taking into account all the relativistic effects in the propagation of light from the primary source to the disk. Given the incident X-ray flux on the disk at each radius, the model estimates the radial ionization profile of the accretion disk assuming a constant disk density 2 (see Kammoun et al 2019, for more details about the ionization estimates). The disk reflection spectrum is computed using the XILLVERD tables for the reflection spectrum from ionized material (García et al 2016), by integrating them from 0.1 keV to infinity.…”

Section: Model Setupmentioning

confidence: 99%

“…https://projects.asu.cas.cz/stronggravity/kynreverb/ 2 The choice of a constant disk density in the estimation of the ionization disk profile should not significantly affect our results because the radial dependence of any realistic density profile is much less significant than the radial decrease of the disk illumination by the lamp-post (see e.g Svoboda et al 2012;Kammoun et al 2019…”

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confidence: 99%

A Hard Look at Thermal Reverberation and Optical/Ultraviolet Lags in NGC 5548

Kammoun

Papadakis

Dovčiak

2019

ApJL

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The UV/optical variations in many AGN are very well correlated, showing delays which increase with increasing wavelength. It is thought that this is due to thermal reprocessing of the X-ray emission by the accretion disk. In this scenario, the variable X-ray flux from the corona illuminates the accretion disk where it is partially reflected, and partially absorbed and thermalized in the disk producing a UV/optical reverberation signal. This will lead to a time lag increasing with wavelength. However, although the shape of the observed time-lags as a function of wavelength is consistent with the model predictions, their amplitude suggested a disk which is significantly hotter than expected. In this work, we estimate the response functions and the corresponding time lags assuming a standard Novikov-Thorne accretion disk illuminated by a point-like X-ray source. We take into account all relativistic effects in the light propagation from the X-ray source to the disk then to the observer. We also compute the disk reflection, accounting for its ionization profile. Our results show that thermal reverberation effects are stronger in sources with large X-ray source height and low accretion rate. We also found that the time lags increase with height and accretion rate. We apply our model to NGC 5548 and we show that the observed lags in this source can be explained by the model, for a source height of ∼ 60 r g and an accretion rate of a few percent of the Eddington limit for a maximally-spinning black hole.

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“…The simulations by Svoboda et al (2012) and Kammoun et al (2019) indicated that the ignorance of the ionization gradient will lead to an increase in the emissivity index.…”

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confidence: 97%

A detailed study on the reflection component for the black hole candidate MAXI J1836−194

Dong

García

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present a detailed spectral analysis of the black hole candidate MAXI J1836-194. The source was caught in the intermediate state during its 2011 outburst by Suzaku and RXTE. We jointly fit the X-ray data from these two missions using the relxill model to study the reflection component, and a steep inner emissivity profile indicating a compact corona as the primary source is required in order to achieve a good fit. In addition, a reflection model with a lamp-post configuration (relxilllp), which is normally invoked to explain the steep emissivity profile, gives a worse fit and is excluded at 99% confidence level compared to relxill. We also explore the effect of the ionization gradient on the emissivity profile by fitting the data with two relativistic reflection components, and it is found that the inner emissivity flattens. These results may indicate that the ionization state of the disc is not constant. All the models above require a supersolar iron abundance higher than ∼ 4.5. However, we find that the high-density version of reflionx can describe the same spectra even with solar iron abundance well. A moderate rotating black hole (a * = 0.84-0.94) is consistently obtained by our models, which is in agreement with previously reported values.2 Yanting Dong et al. INTRODUCTIONGalactic X-ray binaries are believed to be powered by accretion onto stellar-mass black holes or neutron stars. The gases in accretion disc emit thermal radiation in UV/X-ray band (Shakura & Sunyaev 1973). Some fraction of the thermal photons from the disc are then inverse Compton scattered by energetic electrons in the hypothetically hot corona, producing a hard X-ray spectrum in the form of power-law, i.e. N(E) ∝ E −Γ . A fraction of the high-energy photons will irradiate the cold accretion disc, generating the so-called X-ray reflection component (Fabian et al. 1989). The main features of the reflection spectrum are the fluorescent Fe Kα emission line at energies of 6.4-6.97 keV (depend upon the ionization state of the disc) and the Compton hump at 20-30 keV (Young et al. 1999).The profile of the reflection spectrum will be smeared due to the effects of Doppler shift, special relativity, and general relativity if it comes from the inner region of the accretion disc (Fabian et al. 2000). Observationally, the most prominent effect is that the intrinsically narrow Fe Kα line is broadened and skewed to an asymmetric shape. The profile of the broad line, especially the red wing of the line, is directly linked to the inner radius of the accretion disc which is thought to be at the innermost stable circular orbit (ISCO), i.e. R in = R ISCO . Thus, by modelling the broad iron line, we can deduce the spin of the black hole based on the relation between the spin and the ISCO (Bardeen et al. 1972). However, the line profile is readily affected by the subtraction of continuum and other components. Therefore, Reynolds (2014) pointed out that a more accurate measurement of the spin can be achieved by modelling the full reflection spectrum. The spin...

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Steep X-ray reflection emissivity profiles in AGN as the result of radially structured disc ionization

Cited by 32 publications

References 60 publications

Testing the Kerr Black Hole Hypothesis Using X-Ray Reflection Spectroscopy and a Thin Disk Model with Finite Thickness

Testing the Kerr Black Hole Hypothesis Using X-Ray Reflection Spectroscopy and a Thin Disk Model with Finite Thickness

A Hard Look at Thermal Reverberation and Optical/Ultraviolet Lags in NGC 5548

A detailed study on the reflection component for the black hole candidate MAXI J1836−194

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