Theoretical aspects of relativistic spectral features

Karas, V.

doi:10.1002/asna.200610672

Cited by 17 publications

(20 citation statements)

References 96 publications

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“…The observed radiation flux is then obtained by integrating the intrinsic emission over the entire disc surface, from the inner edge (r = r in ) to the outer edge (r = r out ), weighted by the transfer function T (r e , φ e , θ o , a) determining the impact of relativistic energy change (Doppler and gravitational) as well as the lensing effect for a distant observer directed along the inclination angle θ o (see Cunningham 1975;Asaoka 1989;Karas et al 1992;Karas 2006).…”

Section: Black-hole Signatures In Accretion Disc Radiationmentioning

confidence: 99%

Role of emission angular directionality in spin determination of accreting black holes with a broad iron line

Svoboda¹,

Dovčiak²,

Goosmann³

et al. 2009

A&A

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Aims. The spin of an accreting black hole can be determined by spectroscopy of the emission and absorption features produced in the inner regions of an accretion disc. In this work, we discuss the method employing the relativistic line profiles of iron in the X-ray domain, where the emergent spectrum is blurred by general relativistic effects. Methods. Precision of the spectra fitting procedure could be compromised by inappropriate accounting for the angular distribution of the disc emission. Often a unique profile is assumed, invariable over the entire range of radii in the disc and energy in the spectral band. An isotropic distribution or a particular limb-darkening law have been frequently set, although some radiation transfer computations exhibit an emission excess towards the grazing angles (i.e., the limb brightening). By assuming a rotating black hole in the centre of an accretion disc, we perform radiation transfer computations of an X-ray irradiated disc atmosphere (NOAR code) to determine the directionality of outgoing X-rays in the 2−10 keV energy band. Based on these computations, we produce a new extension to the KY software package for X-ray spectra fitting of relativistic accretion discs. Results. We study how sensitive the spin determination is to the assumptions about the intrinsic angular distribution of the emitted photons. The uncertainty of the directional emission distribution translates to 20% uncertainty in the determination of the marginally stable orbit. We implemented the simulation results as a new extension to the KY software package for X-ray spectra fitting of relativistic accretion disc models. Although the parameter space is rather complex, leading to a rich variety of possible outcomes, we find that on average the isotropic directionality reproduces our model data to the best precision. Our results also suggest that an improper use of limb darkening can partly mimic a steeper profile of radial emissivity. We demonstrate these results in the case of XMM-Newton observation of the Seyfert galaxy MCG-6-30-15, for which we construct confidence levels of χ 2 statistics, and on the simulated data for the future X-ray IXO mission. Our simulations, with the tentative IXO response, show a significant improvement that can qualitatively enhance the accuracy of spin determination.

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Section: Black-hole Signatures In Accretion Disc Radiationmentioning

confidence: 99%

Role of emission angular directionality in spin determination of accreting black holes with a broad iron line

Svoboda¹,

Dovčiak²,

Goosmann³

et al. 2009

A&A

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“…In the inner regions of black hole accretion disks, emerging photons are strongly influenced by strong gravity (Kato et al 1998). The framework of General Relativity (GR) is needed to properly determine the resulting spectrum (Fabian et al 2000;Karas 2006;Matt 2006;Miller 2007). Relativistic effects include the energy shifts, both due to special relativity (Doppler effect) and GR (gravitational redshift), as well as the light bending aberration effects that are particularly prominent near the photon orbit: r ph = 3 GM/c 2 = 4.43 M/M ⊙ km for a non-rotating black hole (the radius of r ph decreases with the black hole spin increasing).…”

Section: Introductionmentioning

confidence: 99%

Light-Bending Scenario for Accreting Black Holes in X-Ray Polarimetry

Dovčiak

Muleri²,

Goosmann

et al. 2011

ApJ

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We discuss a model of an X-ray illuminating source above an accretion disk of a rotating black hole. Within the so called lamp-post scheme we compute the expected (observed) polarization properties of the radiation reaching an observer. We explore the dependencies on model parameters, employing Monte Carlo radiation transfer computations of the X-ray reflection on the accretion disk and taking general relativity effects into account. In particular, we discuss the role of the black hole spin, of the observer viewing angle, and of the primary X-ray source distance from the black hole. We give several examples of the resulting polarization degree for two types of exemplary objects -active galactic nuclei and Galactic black holes. In order to assess potential observability of the polarization features, we assume the sensitivity of the proposed New Hard X-ray Mission (NHXM).We examine the energy range from several keV to ∼ 50 keV, so the iron-line complex and the Compton hump are included in our model spectra. We find the resultant polarization degree to increase at the higher end of the studied energy band, i.e. at 20 keV. Thus, the best results for polarimetry of reflection spectra should be achieved at the Compton hump energy region. We also obtain higher polarization degree for large spin values of the black hole, small heights of the primary source, and low inclination angles of the observer.

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“…We define the redshift factor (e.g., Karas )

g = \frac{ν_{observed}}{ν_{local}},

with ν observed and ν local being the radiation frequency measured by the observer in infinity and in the close proximity of the accretion disc, respectively. Aiming to take the relativistic effects into account in the first approximation, we adopt the redshift factor (Pecháček et al )

g = \frac{\sqrt{R ((), R - 3)}}{R + \sin (φ) \sin (I) \sqrt{R - 2 + 4 {((), 1 + normalcos ((), φ) normalsin ((), I))}^{- 1}}},

where R stands for the radial coordinate, φ stands for the azimuthal coordinate, and I stands for the inclination parameter of the system.…”

Section: Reflection Spectral Line From Evolving Accretion Ringsmentioning

confidence: 99%

Tidal disruption events as a site of an evolving relativistic spectral line

Štolc

Karas

2019

Astron Nachr

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In nuclei of galaxies, strong tidal forces can destroy stars passing within a critical distance from the central supermassive black hole (SMBH). Observational signatures of tidal disruption events (TDEs) depend on the environment around the SBMH horizon and the level of its accretion activity. Evidence for optical and ultraviolet spectral features has been reported in TDE flares; nevertheless, to test the effects of general relativity in the immediate vicinity of SMBH, the relativistically broadened and skewed X-ray line would tell us significantly more useful information. This will require to proceed beyond inactive nuclei. To this end, we consider a system where the material from a disrupted star forms a gaseous ring that circularizes near the tidal radius around SMBH, it gradually spreads in radius by viscous processes and resides embedded within a hot corona. In our test calculation, the remnant trail is assumed to be fully circularized and embedded in a hot environment and illuminated by X-rays from a surrounding corona or a jet base of (mild) active galactic nucleus activity. We show the expected effects on the observed profile and the centroid energy. In the future, the evolving spectral features can enhance the diagnostic capability and provide a novel way to reveal the parameters of TDEs in such sources; the distance of the remnant gas from the SMBH, the radial extent of the gaseous trail, and the spin of the SMBH could be measured.

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Theoretical aspects of relativistic spectral features

Cited by 17 publications

References 96 publications

Role of emission angular directionality in spin determination of accreting black holes with a broad iron line

Role of emission angular directionality in spin determination of accreting black holes with a broad iron line

Light-Bending Scenario for Accreting Black Holes in X-Ray Polarimetry

Tidal disruption events as a site of an evolving relativistic spectral line

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