Innermost Part Of Accretion Disk Research Articles

Observational evidences for black-hole existence

Summary. — About forty years ago it was predicted that black holes can be detected as sources of X-ray radiation. Later distortions of spectral lines (Fe Kαline, in particular) for X-ray radiation emitted from the innermost parts of accretion disks were studied. In 1995 these features of Fe Kα-line were discovered with the Japanese ASCA satellite in MCG 6-30-15. Other X-ray missions such as RXTE, XMM-Newton, Chandra, etc. re-discovered features of Fe Kα-lines and other X-ray lines as well. Attempts to fit spectral line shapes lead to conclusions that sometimes the profiles should correspond to radiating regions which are located in the innermost parts of accretion disks where contributions of general relativistic phenomena are extremely important. As an illustration we consider a radiating annulus model to clarify claims about different spectral line profiles. We discuss properties of highly inclined disks and analyze the possibility to evaluate magnetic fields near black-hole horizons.

Shapes of Fe K α lines from annuli near black holes

Recent x-ray observations of microquasars and Seyfert galaxies reveal broad emission lines in their spectra, which can arise in the innermost parts of accretion disks. We consider a radiating annulus model to simulate spectral line shapes. That is a natural approximation for narrow emitting circular rings without extra astrophysical assumptions about emissivity laws. Recently, Muller and Camenzind (Astron. Astrophys. 413, 861 (2004)) presented results of their calculations and classified different types of spectral line shapes and described their origin. We clarified their hypothesis about an origin of double peaked and double horned line shapes. On the basis of results of numerical simulations, we showed that double peaked spectral lines arise almost for any locations of narrow emission rings (annuli), although Muller and Camenzind claimed that such profiles arise for relatively flat spacetimes and typical radii for emission region of about 25r g. We showed that triangular spectral lines could arise for nearest annuli and high inclination angles. We discuss a possibility of appearance of narrow spectral line shapes as a result of spiraling evolution of matter along quasi-circular orbits which could be approximated by narrow annuli.

Measuring the supermassive black hole parameters with space missions

AbstractRecent X-ray observations of microquasars and Seyfert galaxies reveal broad emission lines in their spectra, which can arise in the innermost parts of accretion disks. Recently Müller & Camenzind (2004) classified different types of spectral line shapes and described their origin. Zakharov (2006b) clarified their conclusions about an origin of doubled peaked and double horned line shapes in the framework of a radiating annulus model and discussed s possibility to evaluate black hole parameters analyzing spectral line shapes.

Black Hole Advective Accretion Disks with Optical Depth Transition

We have constructed numerically global solutions of advective accretion disks around black holes that describe a continuous transition between the effectively optically thick outer and optically thin inner disk regions. We have concentrated on models of accretionflows with large mass accretion rates, and we have employed a bridging formula for radiative losses at high and low effective optical depths. Contrary to the models neglecting advection, we have found that global solutions exist for the extended range of accretion rates. The presence of the effectively optically thin regions in the innermost parts of accretion disks with intermediate accretion rates (� 10‐50 Eddington units) results in a significant increase of the plasma temperature in those regions, and this increase can be discriminated in observations. Subject headingg accretion, accretion disks — black hole physics — hydrodynamics

Different types of Fe K α lines from radiating annuli near black holes

Recent X-ray observations of microquasars and Seyfert galaxies reveal the broad emission lines in their spectra, which can arise in the innermost parts of accretion disks. A theoretical analysis of observations and their interpretations were discussed in a number of papers. We consider a radiating annulus model to simulate spectral line shapes. That is a natural approximation for narrow emitting circular rings without extra astrophysical assumptions about emissivity laws. Recently, Müller and Camenzind [Müller, A., Camenzind, M., 2004. A&A 413, 861] presented results of their calculations and classified different types of spectral line shapes and described their origin. We clarified their hypothesis about an origin of double peaked and double horned line shapes. Based on results of numerical simulations we showed that double peaked spectral lines arise almost for any locations of narrow emission rings (annuli) although Müller and Camenzind [Müller, A., Camenzind, M., 2004. A&A 413, 861] suggested that such profiles arise for relatively flat space-times and typical radii for emission region about 25 r g. We showed that triangular spectral lines could arise for nearest annuli and high inclination angles. We discuss a possibility of appearance of narrow spectral line shapes as a result of spiralling evolution of matter along quasi-circular orbits which could be approximated by narrow annuli.

BLACK HOLES: OBSERVATIONAL PROPERTIES

In the article we review observational features of black holes where an influence of a gravitational field is dominant and we must use strong gravitational field approach for GR. Recent X-ray observations of microquasars and Seyfert galaxies reveal broad emission lines in their spectra, which can arise in the innermost parts of accretion disks. Simulations indicate that at low inclination angle the line is measured by a distant observer as characteristic two-peak profile. However, at high inclination angles (> 85°) two additional peaks arise. This phenomenon was discovered by Matt et al. (1993) using the Schwarzschild black hole metric to analyze such an effect. They assumed that the effect is applicable to a Kerr metric far beyond the range of parameters that they exploited. We check and confirm their hypothesis about such a structure of the spectral line shape for the Kerr metric case. We discuss how analysis of the iron spectral line shapes could give an information about an upper limit of magnetic field near black hole horizon.

Signatures of highly inclined accretion disks in galactic black hole candidates and AGNs

Recent X-ray observations of microquasars and Seyfert galaxies reveal broad emission lines in their spectra, which can arise in the innermost parts of accretion disks. Simulations indicate that at low inclination angle the line is measured by a distant observer as characteristic two-peak profile. However, at high inclination angles (>$ 85 \degr$) two additional peaks arise. This phenomenon was discovered by [CITE] using the Schwarzschild black hole metric to analyze such effect. They assumed that the effect is applicable to a Kerr metric far beyond the range of parameters that they exploited. We check and confirm their hypothesis about such a structure of the spectral line shape for the Kerr metric case. We use no astrophysical assumptions about the physical structure of the emission region except the assumption that the region should be narrow enough. Positions and heights of these extra peaks drastically depend on both the radial coordinate of the emitting region (circular hot spot) and the inclination angle. We find that the best conditions to observe this effect are realized at $\theta > 85\degr$ and $r > 5r_{\rm g}$ and may exist in microquasars or low-mass black holes in X-ray binary systems, because there is some precession (and nutation of accretion disks) with not very long time periods (see, for example, the SS433 binary system). The line profiles for different inclination angles and radial coordinates are presented. To analyze the influence of disk models on the spectral line shapes we simulate the line profiles for the Shakura–Sunyaev disk model for accretion disks with the high inclination.

Iron K Line Variability in the Low-Luminosity Active Galactic Nucleus NGC 4579.

We present results of new ASCA observations of the low-luminosity active galactic nucleus (LLAGN) NGC 4579 obtained on 1998 December 18 and 28, and we report on the detection of variability of an iron K emission line. The X-ray luminosities in the 2-10 keV band for the two observations are nearly identical (LX approximately 2x1041 ergs s(-1)), but they are approximately 35% larger than that measured in 1995 July by Terashima et al. An Fe K emission line is detected at 6.39+/-0.09 keV (source rest frame), which is lower than the line energy 6.73+0.13-0.12 keV in the 1995 observation. If we fit the Fe lines with a blend of two Gaussians centered at 6.39 and 6.73 keV, the intensity of the 6.7 keV line decreases, while the intensity of the 6.4 keV line increases, within an interval of 3.5 yr. This variability rules out thermal plasmas in the host galaxy as the origin of the ionized Fe line in this LLAGN. The detection and variability of the 6.4 keV line indicates that cold matter subtends a large solid angle viewed from the nucleus and that it is located within approximately 1 pc from the nucleus. It could be identified with an optically thick standard accretion disk. If this is the case, a standard accretion disk is present at the Eddington ratio of Lbol/LEdd approximately 2x10-3. A broad disk-line profile is not clearly seen, and the structure of the innermost part of accretion disk remains unclear.

Neutron viscosity in accretion disks

Neutron viscosity is investigated as a possible mechanism for the dissipation of kinetic energy into luminosity in the innermost parts of accretion disks around compact objects. Simplified models are presented of the self-consistent, steady-state accretion flows in which viscosity is provided by neutron collisions with accreting ions. Ion temperatures are determined by balancing the heating of ions by viscous dissipation to their cooling by Coulomb collisions with the electrons, providing a self-consistent solution between neutron production and their impact on energy dissipation. The results indicate that neutrons can indeed provide the necessary dissipation to sustain the steady-state accretion of matter at rates of about 10 to the -8th solar mass/yr or less, and electron temperatures of about 100 keV-1 MeV. Neutrons thus present a promising way of modeling bright Galactic X-ray sources.

Innermost parts of accretion disks are thermally and secularly stable

There is strong evidence that various types of exotic astronomical objects (quasars, active galactic nuclei, Cyg X-1, SS433) can be explained by accretion disks orbiting black holes. Most of the proposed models of such objects are plagued by instabilities. It is widely held, for example, that all accretion disks must be thermally and secularly unstable in their innermost parts, which seems to be in direct conflict with observations. Much effort has been made to find a stabilizing mechanism operating in the innermost parts of the disks. Here I show that such a mechanism does exist. It is of general relativistic origin, is purely mechanical—operating independently of viscosity and other micro-physical processes—and is similar to the mass loss caused by Roche lobe overflow in close binaries.