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1.
We calculate the polarization of the radiation from an optically thick accretion disk with a vertical averaged magnetic field. The polarization arises from the scattering of light by free electrons in a magnetized disk plasma. The Faraday rotation of the polarization plane during the propagation of a photon in a medium with a magnetic field is considered as the main effect. We discuss various models of optically thick accretion disks with a vertical averaged magnetic field. Our main goal is to derive simple asymptotic formulas for the polarization of radiation in the case where the Faraday rotation angle Ψ ≫ 1 at the Thomson optical depth τ = 1. The results of our calculations allow the magnetic field strength in the region of the marginally stable orbit near a black hole to be estimated from polarimetric observations, including X-ray observations expected in the future. Since the polarization spectrum of the radiation strongly depends on the accretion disk model, a realistic physical model of the accretion disk can be determined from data on the polarization of its radiation.  相似文献   

2.
Magnetic fields in an accretion disk around the central black hole can modify the size of the innermost stable circular orbit (ISCO) and can produce a difference to the classical Novikov‐Thorne radius. We estimated the ISCO magnetic field strength from the polarimetric observations of the accretion‐disk radiation. This estimate is obtained taking into account the effect of the Faraday rotation of the polarization plane at the distance of the mean free path of photons between successive electron scattering events. We present the new method for estimating the ISCO radius in the accretion disk, i.e. in the nearest vicinity of a central black hole. Our estimates confirmed the Frolov, Shoom & Tzounis (2014) and Ranea‐Sandoval & Garcia (2015) conclusion that the magnetic field in the accretion disk decreases the size of the innermost stable circular orbit. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

3.
The magnetic field in an accretion disk is estimated assuming that all of the angular momentum within prescribed accretion disk radii is removed by a jet. The magnetic field estimated at the base of the jet is extrapolated to the blazar emission region using a model for a relativistic axisymmetric jet combined with some simplifying assumptions based on the relativistic nature of the flow. The extrapolated magnetic field is compared with estimates based upon the synchrotron and inverse Compton emission from three blazars, MKN 501, MKN 421 and PKS 2155-304. The magnetic fields evaluated from pure synchrotron self-Compton models are inconsistent with the magnetic fields extrapolated in this way. However, in two cases inverse Compton models in which a substantial part of the soft photon field is generated locally agree well, mainly because these models imply magnetic field strengths consistent with an important Poynting Flux component. This comparison is based on estimating the mass accretion rate from the jet energy flux. Further comparisons along these lines will be facilitated by independent estimates of the mass accretion rate in blazars and by more detailed models for jet propagation near the black hole.  相似文献   

4.
Estimates of magnetic fields for a number of active galactic nuclei are presented. These estimates are based on the observed polarization degrees and position angles of broad Hα lines and in the nearby continuum and on asymptotic analytical formulas for the Stokes parameters of the radiation emerging from a magnetized accretion disk (the Milne problem in a magnetized atmosphere). The characteristic observed feature of the wavelength dependence of the polarization degree inside the line—a minimum at the center and a fast increase of the position angle from one wing to another—can be explained by the superposition of resonance emission from two or more clouds located in the right (Keplerian velocity directed away from the observer) and left (Keplerian velocity directed toward the observer) parts of the orbit in the rotating magnetized accretion disk. The main component in our mechanism is the azimuthal magnetic field in the disk. The presence of a magnetic field perpendicular to the disk plane (which is usually weaker than the azimuthal field) results in the asymmetry of the distribution of the polarization degree and position angle inside the line. The inferred magnetic field strengths at the galactocentric distances where broad lines are emitted can be used to estimate the magnetic fields in the region of the centermost stable orbit and at the horizon of the central black hole, using the power-law dependence of the magnetic field strength corresponding to the standard model of the accretion disk.  相似文献   

5.
Various relations are found between the key parameters of black holes and active galactic nuclei. Some have a statistical property, others follow from the theoretical consideration of the evolution of these objects. In this paper we use a recently discovered empirical relation between the characteristic frequency of quasi-periodic oscillations of radiation ν br of black holes, their masses and matter accretion rates to determine the magnetic field strength B H at the black hole event horizon. Since the characteristic frequency can be determined from observations, the use of a new relation for the estimations of magnetic field B H can yield more definite results, since we are decreasing the number of the unknown or poorly-determined parameters of objects (it especially concerns the accretion rate Ṁ). The typical values which we have found are B H ≃ 108G for the stellar mass black holes, and B H ≃ 104G for the supermassive black holes. Besides, we demonstrate that if the linear polarization of an object is caused by the radiation of a magnetized accretion disk, then the degree of observable polarization is p ∼ ν br −1/2.  相似文献   

6.
In this paper we demonstrate that the wavelength dependence of polarization degree and position angle allows us to derive the distribution of magnetic field in accretion disc. The polarized radiation arises due to scattering of emission light by electrons in a magnetized optically thick accretion disc. Faraday rotation of polarization plane is taken into consideration. Through wavelength dependence of polarization it is possible to derive the value of the magnetic Prandtl number in the accretion disc plasma. The power law index of the polarization wavelength dependence is related with the radial distribution of magnetic field in an accretion disc. This allows us to test the various models of an accretion disc around the central black hole.  相似文献   

7.
本文讨论了具有磁场的几何厚吸积盘结构和辐射。结果表明:磁场的存在明显地影响吸积盘的总光度和形状。这种模型可以解释类星体的辐射幂谱分布和高度偏振现象。它是类星体主要辐射区域的一种合理模型。  相似文献   

8.
High-frequency quasi-periodic variations (HF QPOs) in the X-ray light curves of black hole X-ray novae can be understood as oscillations of the accretion disk in a nonlinear 3:2 resonance. An m = 0 vertical oscillation near a black hole modulates the X-ray emission through gravitational lensing (light-bending) at the source. Certain oscillations of the accretion disk will also modulate the mass accretion rate, and in neutron-star systems this would lead to nearly periodic variations in brightness of the luminous boundary layer on the stellar surface – the amplitude of the neutron-star HF QPOs would be thus increased relative to the black hole systems. The “kHz QPOs” in black holes are in the hecto-Hz range.  相似文献   

9.
We show that a fundamental choice between various models of an accretion disk around a black hole can be made based on the spectral wavelength distribution of the polarization. This conclusion is based on the possibility of comparing the observed spectral distribution of the polarization with its theoretical values obtained in various accretion disk models. The expected power-law wavelength (frequency) dependences of the polarization for various accretion disk models known in the literature are presented in the table.  相似文献   

10.
A hypothesis is being put forward that the formation of jets in the nuclei of radio galaxies is due to a high-speed energy excretion (explosion) in the accretion disk around a massive black hole. The explosion can be induced, for example, by a fall of the star into the black hole. For the accretion disk featuring an exponential high-density distribution, an asymmetrical explosion can be obtained: the shock front moves in the direction of decreasing the density accelerately and achieves the relativistic velocity swiftly, carrying away the most fraction of the explosion energy. Radio emission of the jet involves synchrotron radiation of relativistic electrons which are accelerated by such shock wave in the magnetic field driven up by the shock front.  相似文献   

11.
The peaks in the spectra of the accretion disks surrounding massive black holes in quasars are in the far-UV or soft X-ray band, which are usually not observed. However, in the disk corona model, soft photons from the disk are Comptonized to high energy in the hot corona, and the hard X-ray spectra(luminosity and spectral shape) contain information on the incident spectra from the disk. The values of black hole spin parameter a*are inferred from the spectral fitting, which are spread over a large range, ~-0.94 to 0.998. We find that the inclination angles and mass accretion rates are well determined by the spectral fitting, but the results are sensitive to the accuracy of black hole mass estimates. No tight constraints on the black hole spins are achieved, if the uncertainties in black hole mass measurements are a factor of four,which are typical for the single-epoch reverberation mapping method. Recently, the accuracy of black hole mass measurement has been significantly improved to 0.2- 0.4 dex with the velocity resolved reverberation mapping method. The black hole spin can be well constrained if the mass measurement accuracy is50%. In the accretion disk corona scenario, a fraction of power dissipated in the disk is transported into the corona, and therefore the accretion disk is thinner than a bare disk for the same mass accretion rate,because the radiation pressure in the disk is reduced. We find that the thin disk approximation, H/R0.1,is still valid if 0.3 m 0.5, provided half of the dissipated power is radiated in the corona above the disk.  相似文献   

12.
We apply the disk-corona evaporation model (Meyer & Meyer-Hofmeister) originally derived for dwarf novae to black hole systems. This model describes the transition of a thin cool outer disk to a hot coronal flow. The mass accretion rate determines the location of this transition. For a number of well-studied black hole binaries, we take the mass flow rates derived from a fit of the advection-dominated accretion flow (ADAF) model to the observed spectra (for a review, see Narayan, Mahadevan, & Quataert) and determine where the transition of accretion via a cool disk to a coronal flow/ADAF would be located for these rates. We compare this with the observed location of the inner disk edge, as estimated from the maximum velocity of the Halpha emission line. We find that the transition caused by evaporation agrees with this determination in stellar disks. We also show that the ADAF and the "thin outer disk + corona" are compatible in terms of the physics in the transition region.  相似文献   

13.
Recent results of the gamma-ray Cherenkov astronomy definitely prove the existence of fast variability in the very high energy (V.H.E.) gamma-ray flux of some active galactic nuclei. The BL Lac PKS 2155-304 for instance showed variations down to a few minutes time scale. From standard light travel time argument, these variations put extremely strong constraints on the size of the TeV emitting zone, which has to be of the order of a few Schwarzschild radius, even for high values of the relativistic Doppler factor of the emitting jets. Such discovery is a challenge for particle acceleration scenarios, which have to imagine efficient acceleration processes at work in a very compact zone. Eventually, the immediate vicinity of the central black hole appears as the most conservative choice for the location of the TeV emission region of active galactic nuclei. In this paper, we propose a two-step mechanism for charged particle acceleration in the magnetosphere of a massive black hole surrounded by an accretion disk. Particles first gain energy by a stochastic process during the accretion phase. It is shown that effective proton acceleration up to energies 1017–1019 eV is possible in a low-luminosity magnetized accretion disk with 2D turbulent motion. The distribution function of energetic protons over energies is a power law function with typical index ≃−1. Here electrons are not very efficiently accelerated because of their drastic losses by synchrotron radiation. In a second time, part of the fast particles escape from the disk and are then entrained by the magnetic structure above the disk, in the rotating black hole magnetosphere. They thus gain additional energy by direct centrifugal mechanism, up to about 1020 eV for the protons and to 10–100 TeV for the electrons when they cross the light cylinder surface. Such energetic particles can further radiate in the TeV spectral range observed by Cherenkov experiments as HESS, MAGIC and VERITAS. Energetic protons can produce γ-radiation in the energy band 1 GeV–100 TeV and above mainly by nuclei collisions with the disk matter, clouds, or ambient low energy photons. Energetic electrons can also reach the required spectral range by inverse Compton emission. However their acceleration is less efficient due to heavy radiation losses, and only gained by centrifugal process during the second phase of the whole mechanism we describe. Our present analysis would therefore favor hadronic scenarios for TeV emission of active galactic nuclei. It is tempting to relate long term variability over years of TeV active galactic nuclei to the first stochastic acceleration phase, which also provides the needed power law particle distributions, while short term variability over minutes is more likely due to perturbations of the second fast direct acceleration phase.  相似文献   

14.
The highest efficiency of converting rest mass into energy by accreting matter into a Kerr black hole is approximately 31% (Thorne 1974). We propose a new process in which periods of accretion from a thin disk, and the associated spin-up of the black hole, alternate with the periods of no accretion and magnetic transfer of energy from the black hole to the disk. These cycles can repeat indefinitely, at least in principle, with the black hole mass increasing by approximately 66% per cycle and up to approximately 43% of accreted rest mass radiated away by the disk.  相似文献   

15.
The nature of Ultraluminous X-ray Sources – X-ray sources which exceed the Eddington luminosity for a ∼10 M ⊙ black hole – remains a mystery. One possible explanation is an inhomogeneous accretion disk around a solar mass black hole where photon transport through radiation-pressure dominated “photon bubbles” can lead to super-Eddington accretion. While previous studies of this model have focused primarily on its radiation-hydrodynamics aspects, here we explore some observational implications of such a model with a Monte Carlo–Fokker Planck radiation transport code.  相似文献   

16.
具有不同质量的恒星在耗尽其热核能源后,最终可能会坍缩成为性质完全不同的致密天体,如白矮星、中子星或者黑洞。从20世纪30年代起,黑洞的观测及其证认一直是天体物理学的研究热点之一。首先简要地回顾了恒星级黑洞的形成及其候选天体的研究历史;然后介绍了如何从观测上证认恒星级黑洞:接着详细讨论了恒星级黑洞的质量和自转参数的测量方法;最后介绍恒星级黑洞观测及其证认的最新研究进展,并做出结论:目前已经有充分的证据宣告在部分吸积X射线双星中存在恒星级黑洞。  相似文献   

17.
Hardly any of the observed black hole accretion disks in X-ray binaries and active galaxies shows constant flux. When the local stochastic variations of the disk occur at specific regions where a resonant behaviour takes place, there appear the quasi-periodic oscillations (QPOs). If the global structure of the flow and its non-linear hydrodynamics affects the fluctuations, the variability is chaotic in the sense of deterministic chaos. Our aim is to solve a problem of the stochastic versus deterministic nature of the black hole binary variabilities. We use both observational and analytic methods. We use the recurrence analysis and we study the occurence of long diagonal lines in the recurrence plot of observed data series and compare it to the surrogate series. We analyze here the data of two X-ray binaries – XTE J1550-564 and GX 339-4 observed by Rossi X-ray Timing Explorer. In these sources, the non-linear variability is expected because of the global conditions (such as the mean accretion rate) leading to the possible instability of an accretion disk. The thermal-viscous instability and fluctuations around the fixed-point solution occurs at high accretion rate, when the radiation pressure gives dominant contribution to the stress tensor.  相似文献   

18.
The structure and magnitude of the electromagnetic field produced by a rotating accretion disk around a black hole were determined. The disk matter is assumed to be a magnetized plasma with a frozenin poloidal magnetic field. The vacuum approximation is used outside the disk.  相似文献   

19.
通过几十年的观测研究, 黑洞X射线双星(X-Ray Binary, XRB)部分特征被揭示. 然而, 吸积盘结构尚不确定. 黑洞XRB功率密度谱的截断频率与准周期振荡(Quasi Periodic Oscillation, QPO)的相关性质(W-K关系)可以限制吸积盘结构. 利用慧眼-HXMT (Hard X-ray Modulation Telescope)观测到的5个黑洞XRB的数据, 对黑洞XRB的W-K关系进行了研究, 结果表明在慧眼-HXMT观测的3个探测器能段中W-K关系成立. 此外在MAXI J1535-571之中存在截断频率和吸积盘内半径的相关关系, 这和截断的吸积盘结构一致. 如果观测到的功率密度谱来自质量吸积率的扰动传播, 可以推测吸积盘内半径接近最内圆形稳定轨道, 此黑洞可能是高自旋系统.  相似文献   

20.
Naturally occurring water vapor maser emission at 1.35 cm wavelength provides an accurate probe for the study of accretion disks around highly compact objects, thought to be black holes, in the centers of active galaxies. Because of the exceptionally fine angular resolution, 200 microarcseconds, obtainable with very long baseline interferometry, accompanied by high spectral resolution, <0.1 km s-1, the dynamics and structures of these disks can be probed with exceptional clarity. The data on the galaxy NGC 4258 are discussed here in detail. The mass of the black hole binding the accretion disk is 3·9 × 107 M⊙. Although the accretion disk has a rotational period of about 800 years, the physical motions of the masers have been directly measured with VLBI over a period of a few years. These measurements also allow the distance from the earth to the black hole to be estimated to an accuracy of 4 per cent. The status of the search for other maser/black hole candidates is also discussed.  相似文献   

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