Determination of Supermassive Black Hole Spins Based on the Standard Shakura–Sunyaev Accretion Disk Model and Polarimetric Observations     

V.?L.?Afanasiev  Yu.N.?GnedinEmail author  M.Yu.?Piotrovich  S.?D.?Buliga  T.?M.?Natsvlishvili 《Astronomy Letters》2018,44(6):362-369

Based on spectropolarimetry for 47 type 1 active galactic nuclei observed with the 6-m BTA telescope, we have estimated the spins of the supermassive black holes at the centers of these galaxies. We have determined the spins based on the standard Shakura–Sunyaev accretion disk model. About 70% of the investigated active galactic nuclei are shown to have Kerr supermassive black holes with a dimensionless spin greater than 0.9.  相似文献   

The magnetic-field structure in a stationary accretion disk     

M. Yu. Piotrovich  N. A. Silant’ev  Yu. N. Gnedin  T. M. Natsvlishvili  S. D. Buliga 《Astronomy Reports》2016,60(5):486-497

The magnetic-field structure in regions of stationary, planar accretion disks around active galactic nuclei where general-relativistic effects can be neglected (from 10 to 200 gravitational radii) is considered. It is assumed that the magnetic field in the outer edges of the disk, which forms in the magnetosphere of the central black hole during the creation of the relativisitic jets, corresponds to the field of a magnetic dipole perpendicular to the plane of the disk. In this case, the azimuthal field component B_φ in the disk arises due to the presence of the radial field B_ρ and the azimuthal velocity component U_φ. The value of the magnetic field at the inner radius of the disk is taken to correspond to the solution of the induction equation in a diffusion approximation. Numerical solutions of the induction equation are given for a number of cases.  相似文献   

Spectropolarimetric Observations of Magnetic White Dwarfs with the SAO 6-m Telescope     

V. L. Afanas’ev  M. Yu. Piotrovich  Yu. N. Gnedin  S. D. Buliga  T. M. Natsvlishvili 《Astronomy Reports》2018,62(2):138-143

The results of spectropolarimetric observations of a number of magnetic white dwarfs obtained on the 6-m optical telescope of the Special Astrophysical Observatory are presented. The observations were carried out using the SCORPIO focal aperture-ratio reducer in a spectropolarimetric regime. Two characteristic dependences of the degree of polarization on the wavelength are observed. For one group of objects, the degree of linear polarization grows with wavelength, suggesting that the alignment of atoms and molecules in Rydberg states in the atmosphere of the white dwarf due to the action of its magnetic field influences scattering processes. The second group of objects displays an increase in the degrees of both linear and circular polarization with wavelength, providing evidence for the presence of protoplanetary disks around these magnetic white dwarfs, in which the alignment of circumstellar grains leads to the observed behavior.  相似文献   

Spectropolarimetric observations of active galactic nuclei with the 6-m BTA telescope     

V. L. Afanasiev  N. V. Borisov  Yu. N. Gnedin  T. M. Natsvlishvili  M. Yu. Piotrovich  S. D. Buliga 《Astronomy Letters》2011,37(5):302-310

We present the results of our spectropolarimetric observations for a number of active galactic nuclei (AGNs) carried out at the 6-m telescope with the SCORPIO focal reducer. The derived wavelength dependences of the polarization have been analyzed by taking into account the Faraday rotation of the polarization plane on the photon mean free path in a magnetized accretion disk. As a result, based on traditional accretion disk models, we have determined the magnetic field strength and distribution and a number of physical parameters of the accreting plasma in the region where the optical radiation is generated.  相似文献   

Magnetic fields and quasi-periodic oscillations of black hole radiation     

M. Yu. Piotrovich  N. A. Silant’ev  Yu. N. Gnedin  T. M. Natsvlishvili 《Astrophysical Bulletin》2011,66(3):320-324

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   

Radio emission of the cosmic gamma-ray burst GRB 080319B: Observations of the afterglow using telescopes of the Institute of Applied Astronomy of the Russian Academy of Sciences     

M. A. Kharinov  A. M. Finkel’shteĭn  A. V. Ipatov  O. A. Tsiopa  Yu. N. Gnedin  M. Yu. Piotrovich 《Astronomy Reports》2010,54(9):853-860

Results of radio observations of the cosmic gamma-ray burst GRB 080319B at 8.45 GHz during the afterglow are reported. The observations were carried out on telescopes of the Zelenchukskaya and Svetloe Observatories of the Institute of Applied Astronomy, Russian Academy of Sciences. Two outbursts in the radio brightness were detected in the afterglow of GRB 080319B. A total of 148 radio observations were performed at 3.5, 6.2, and 13 cm. The observations were conducted in a mode with smooth scanning in elevation, which was also used to update the flux densities of the primary reference sources. The first powerful radio outburst was recorded on March 28, 2008, 6.86^d after the gamma-ray burst, when the maximum flux density was F _{8.45 GHz} = 44 ± 12 mJy. Almost two months later, a second increase in the radio brightness was observed. The flux density monotonically increased from 19 mJy (59.55^d) to 34mJy (59.79^d) over 6.5 h; 1.17 d later, the flux density fell to 12mJy.At this last epoch, the radio flux demonstrated variability within 3σ on timescales of 9^d−10^d. The detected radio brightness increases are interpreted in terms of MHD interactions of a fast plasma outflow with a cloud of inhomogeneous surrounding medium. This interaction is accompanied by restructuring of the relativistic plasma outflow; the analysis of this process has been carried out.  相似文献   

Spectral distribution of the polarized radiation from standard accretion disks in Active Galactic Nuclei: Observational analysis     

V. L. Afanas’ev  N. V. Borisov  Yu. N. Gnedin  S. D. Buliga  T. M. Natsvlishvili  M. Yu. Piotrovich 《Astronomy Reports》2014,58(10):725-732

Spectropolarimetric observations of a number of Active Galactic Nuclei obtained using the SCORPIO-2 aperture focal reducer installed on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences are used to estimate physical parameters of these objects. The measured polarization and its wavelength dependence are consistent with the expectations of a standard accretion-disk model taking into account the effect of Faraday depolarization over the mean free path of the emitted photons. Estimates of the magnetic field in the accretion disk near the innermost stable orbit and the spin of the accreting central black hole are obtained. It is concluded that supermassive black holes with standard accretion disks and equal magnetic and radiative pressures are primarily Kerr black holes.  相似文献   

Topology of magnetic field and polarization in accretion discs of AGN     

Y. N. Gnedin  S. D. Buliga  N. A. Silant’ev  T. M. Natsvlishvili  M. Y. Piotrovich 《Astrophysics and Space Science》2012,342(1):137-145

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   

Determining the spins of supermassive black holes in Active Galactic Nuclei based on spectropolarimetric observations     

Yu. N. Gnedin  V. L. Afanasiev  N. V. Borisov  M. Yu. Piotrovich  T. M. Natsvlishvili  S. D. Buliga 《Astronomy Reports》2012,56(8):573-577

Strong constraints are obtained for the spins of supermassive black holes in a number of Active Galactic Nuclei. These estimates are based on spectropolarimetric data, obtained mainly on the 6-m telescope of the Special Astrophysical Observatory, as well as data on the kinetic power of relativistic jets. The magnetic fields at the innermost stable Keplerian orbit in the accretion disk and at the event horizon of the supermassive black hole are estimated. These data are used to place strong constraints on the spins of supermassive black holes in Active Galactic Nuclei.  相似文献   

Subgrade-reinforcement techniques for the dangerously deforming sections of railway lines in the north of the Russian Far East     

Alexey Piotrovich  Svetlana Zhdanova 《寒旱区科学》2017,9(3):197-204

This paper lists difficult railway construction conditions that are typical for the northern areas of the Russian Far East. Permafrost-bound issues of railway and highway construction and operation are described. Some of the authors'' developments for subgrade stabilization in the foregoing conditions are given as examples.  相似文献