Showing 1–33 of 33 results for author: Piotrovich, M Y

Spins of SMBHs in distant low luminosity AGNs

Authors: M. Yu. Piotrovich, S. D. Buliga, T. M. Natsvlishvili

Abstract: We estimated radiative efficiency, spin and SMBH mass values for sample of 33 distant low luminosity AGNs. The distribution of the estimated spin values (majority of objects have a spin greater than 0.8) is fairly typical for many types of AGNs. The dependence of the estimated spin values on the estimated SMBH masses shows strong correlation between them, which suggests a rapid increase in spin wi… ▽ More We estimated radiative efficiency, spin and SMBH mass values for sample of 33 distant low luminosity AGNs. The distribution of the estimated spin values (majority of objects have a spin greater than 0.8) is fairly typical for many types of AGNs. The dependence of the estimated spin values on the estimated SMBH masses shows strong correlation between them, which suggests a rapid increase in spin with mass, i.e. that the main mechanism of mass growth in this case is disk accretion. We did not find any significant qualitative differences in the spin characteristics between our objects and objects of other types considered in the paper. △ Less

Submitted 27 June, 2025; originally announced June 2025.

Comments: 12 pages, 12 figures

MAD-Accretion Scenario in High-Mass X-Ray Binaries with Neutron Stars

Authors: N. R. Ikhsanov, M. Yu. Piotrovich, N. G. Beskrovnaya

Abstract: The wind-fed accretion of gas with an intrinsic magnetic field onto neutron stars in high-mass X-ray binaries (HMXBs) is discussed. The criteria for the implementation of quasi-spherical accretion in the system, the formation of a Keplerian accretion disk and a non-Keplerian magnetically arrested disk (MAD-accretion scenario) are formulated. It is shown that the period of the equilibrium rotation… ▽ More The wind-fed accretion of gas with an intrinsic magnetic field onto neutron stars in high-mass X-ray binaries (HMXBs) is discussed. The criteria for the implementation of quasi-spherical accretion in the system, the formation of a Keplerian accretion disk and a non-Keplerian magnetically arrested disk (MAD-accretion scenario) are formulated. It is shown that the period of the equilibrium rotation of a neutron star in the MAD-accretion scenario, in addition to the parameters of the binary system, is also determined by the velocity, temperature, and degree of magnetization of the stellar wind of its massive companion. Within the hypothesis of the equilibrium rotation, we have estimated the parameters of the stellar wind for the most fully-studied quasi-equilibrium accreting pulsars in the HMXBs corresponding to the criteria for the MAD-accretion scenario implementation. We show that the period of the equilibrium rotation of a neutron star in the system, all other things being equal, increases with the growth of the magnetization degree of the stellar wind component of its massive companion flowing out in the plane of the system's orbit. Therefore, the periods of accreting pulsars in systems with similar parameters can differ from each other by several orders of magnitude and, under favorable conditions, reach values of several thousand and even tens of thousands of seconds. △ Less

Submitted 15 May, 2025; originally announced May 2025.

Comments: 14 pages

Estimating the spins of supermassive black holes in distant ultraluminous quasars

Authors: M. Yu. Piotrovich, S. D. Buliga, T. M. Natsvlishvili

Abstract: We estimated spin, inclination angle and corresponding SMBH mass values for sample of extremely distant (6 < z < 7.5) ultraluminous quasars. The estimated spin values are on average greater that 0.9 and the spin distribution has a characteristic appearance, similar to ones obtained for other types of AGNs and quasars. The dependence of estimated parameters on each other shows strong correlations b… ▽ More We estimated spin, inclination angle and corresponding SMBH mass values for sample of extremely distant (6 < z < 7.5) ultraluminous quasars. The estimated spin values are on average greater that 0.9 and the spin distribution has a characteristic appearance, similar to ones obtained for other types of AGNs and quasars. The dependence of estimated parameters on each other shows strong correlations between them, from which we can assume that in this early quasars the growth of SMBHs mass should occur mainly due to disk accretion with high accretion rate, which very effectively increases the spin. △ Less

Submitted 13 May, 2025; originally announced May 2025.

Comments: 15 pages, 12 figures

Red quasars: estimation of SMBH spin, mass and accretion disk inclination angle

Authors: M. Yu. Piotrovich, S. D. Buliga, T. M. Natsvlishvili

Abstract: We estimated values of spin, mass and inclination angle for sample of 42 red quasars. Our estimations show that 2 objects: F2MS~J1113+1244 and F2MS~J1434+0935 with highest Eddington ratios may have geometrically thick disk. Six objects: SDSS~J0036-0113, S82X~0040+0058, S82X~0118+0018, S82X~0303-0115, FBQS~J1227+3214, S82X~2328-0028 may have "retrograde" rotation. Analysis of estimated spin values… ▽ More We estimated values of spin, mass and inclination angle for sample of 42 red quasars. Our estimations show that 2 objects: F2MS~J1113+1244 and F2MS~J1434+0935 with highest Eddington ratios may have geometrically thick disk. Six objects: SDSS~J0036-0113, S82X~0040+0058, S82X~0118+0018, S82X~0303-0115, FBQS~J1227+3214, S82X~2328-0028 may have "retrograde" rotation. Analysis of estimated spin values shows that red quasar population may contain Seyfert galaxies and NLS1. △ Less

Submitted 7 October, 2024; originally announced October 2024.

Comments: 10 pages, 9 figures

Probing AGN with spectropolarimetry: accretion disk and SMBH parameters

Authors: M. Yu. Piotrovich, E. S. Shablovinskaya, E. A. Malygin, S. D. Buliga, T. M. Natsvlishvili

Abstract: The interaction of a supermassive black hole with the matter of an accretion disk in the presence of a magnetic field is the key mechanism of energy release in active galactic nuclei. However, determining the physical parameters of this system, such as the spin and mass of the black hole, the shape and parameters of the rotation of the accretion disk, and the geometry of the magnetic field in the… ▽ More The interaction of a supermassive black hole with the matter of an accretion disk in the presence of a magnetic field is the key mechanism of energy release in active galactic nuclei. However, determining the physical parameters of this system, such as the spin and mass of the black hole, the shape and parameters of the rotation of the accretion disk, and the geometry of the magnetic field in the accretion disk is a complex and not completely solved problem. We have previously shown, based on our numerical models, that these estimates can be obtained from just three parameters: the black hole mass, bolometric luminosity, and optical polarization. In this paper, we estimate the accretion disk and black hole parameters for a sample of 14 type 1 Seyfert galaxies. Using the spectropolarimetric data obtained by us, we selected only those objects in which the polarization of optical radiation is generated mainly by the mechanism in the accretion disk. Despite the small statistics, our results for such a sample are consistent with our previous conclusions and show a discrepancy between the disk magnetic field parameters and the classical Shakura-Sunyaev disk model. △ Less

Submitted 22 September, 2023; originally announced September 2023.

Comments: 9 pages, 5 figures

Determination of supermassive black hole spins in local active galactic nuclei

Authors: M. Yu. Piotrovich, S. D. Buliga, T. M. Natsvlishvili

Abstract: We estimated the radiative efficiency and spin value for a number of local active galactic nuclei with z < 0.34 using 3 popular models connecting the radiative efficiency with such parameters of AGNs as mass of supermassive black hole, angle between the line of sight and the axis of the accretion disk and bolometric luminosity. Analysis of the obtained data shown that the spin value decreases with… ▽ More We estimated the radiative efficiency and spin value for a number of local active galactic nuclei with z < 0.34 using 3 popular models connecting the radiative efficiency with such parameters of AGNs as mass of supermassive black hole, angle between the line of sight and the axis of the accretion disk and bolometric luminosity. Analysis of the obtained data shown that the spin value decreases with cosmic time, which is in agreement with results of theoretical calculations for low redshift AGNs of other authors. Also we found that the spin value increases with the increasing mass of SMBH and bolometric luminosity. This is the expected result that corresponds to theoretical calculations. Analysis of the distribution of the spin values shown a pronounced peak in the distribution in 0.75 < a < 1.0 range. ~ 40% of objects have spin a > 0.75 and ~ 50% of objects have spin a > 0.5. This results are in a good agreement with our previous results and with the results of other authors. △ Less

Submitted 21 May, 2022; originally announced May 2022.

Comments: 7 pages, 6 figures

Search for wormhole candidates in active galactic nuclei: radiation from colliding accreting flows

Authors: M. Yu. Piotrovich, S. V. Krasnikov, S. D. Buliga, T. M. Natsvlishvili

Abstract: The underlying hypothesis of this work is that the active galactic nuclei (AGNs) are wormhole mouths rather than supermassive black holes (SMBHs). Under some - quite general - assumptions such wormholes may emit gamma radiation as a result of a collision of accreting flows inside the wormholes. This radiation has a distinctive spectrum much different from those of jets or accretion disks of AGNs.… ▽ More The underlying hypothesis of this work is that the active galactic nuclei (AGNs) are wormhole mouths rather than supermassive black holes (SMBHs). Under some - quite general - assumptions such wormholes may emit gamma radiation as a result of a collision of accreting flows inside the wormholes. This radiation has a distinctive spectrum much different from those of jets or accretion disks of AGNs. An observation of such radiation would serve as evidence of the existence of wormholes. △ Less

Submitted 21 August, 2020; originally announced August 2020.

Comments: 4 pages, 2 figures

Determination of magnetic field strength on the event horizon of supermassive black holes in active galactic nuclei

Authors: M. Yu. Piotrovich, A. G. Mikhailov, S. D. Buliga, T. M. Natsvlishvili

Abstract: We estimated the magnetic field strength at the event horizon for a sample of supermassive black holes (SMBHs) in active galactic nuclei (AGNs). Our estimates were made using the values of the inclination angles of the accretion disk to the line of sight, that we obtained previously from spectropolarimetric observations in the visible spectrum. We also used published values of full width at half m… ▽ More We estimated the magnetic field strength at the event horizon for a sample of supermassive black holes (SMBHs) in active galactic nuclei (AGNs). Our estimates were made using the values of the inclination angles of the accretion disk to the line of sight, that we obtained previously from spectropolarimetric observations in the visible spectrum. We also used published values of full width at half maximum (FWHM) of spectral line $H_β$ from broad line region, masses of SMBHs and luminosity of AGNs at 5100 angstrom. In addition we used literature data on the spins of SMBHs obtained from their X-ray spectra. Our estimates showed that the magnetic field strength at the event horizon of the majority of SMBHs in AGNs ranges from several to tens of kG and have mean values of about $10^4$G. At the same time, for individual objects, the fields are significantly larger - of the order of hundreds kG or even 1 MG. △ Less

Submitted 14 April, 2020; originally announced April 2020.

Comments: 8 pages, 8 figures

Criterions for retrograde rotation of accreting black holes

Authors: A. G. Mikhailov, M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili, S. D. Buliga

Abstract: Rotating supermassive black holes produce jets and their origin is connected to magnetic field that is generated by accreting matter flow. There is a point of view that electromagnetic fields around rotating black holes are brought to the hole by accretion. In this situation the prograde accreting disks produce weaker large-scale black hole threading magnetic fields, implying weaker jets that in r… ▽ More Rotating supermassive black holes produce jets and their origin is connected to magnetic field that is generated by accreting matter flow. There is a point of view that electromagnetic fields around rotating black holes are brought to the hole by accretion. In this situation the prograde accreting disks produce weaker large-scale black hole threading magnetic fields, implying weaker jets that in retrograde regimes. The basic goal of this paper is to find the best candidates for retrograde accreting systems in observed active galactic nuclei. We show that active galactic nuclei with low Eddington ratio are really the best candidates for retrograde systems. This conclusion is obtained for kinetically dominated FRII radio galaxies, flat spectrum radio loud narrow line Seyfert I galaxies and a number of nearby galaxies. Our conclusion is that the best candidates for retrograde systems are the noticeable population of active galactic nuclei in the Universe. This result corresponds to the conclusion that in the merging process the interaction of merging black holes with a retrograde circumbinary disk is considerably more effective for shrinking the binary system. △ Less

Submitted 9 March, 2018; originally announced March 2018.

Comments: 5 pages

Constraints on Spin of a Supermassive Black Hole in Quasars with Big Blue Bump

Authors: M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili, S. D. Buliga

Abstract: We determined the spin value of supermassive black hole (SMBH) in active galactic nuclei (AGN) with investigated ultraviolet-to-optical spectral energy distribution, presented in the sample of Shang et al. (2005). The estimates of the spin values have been produced at the base of the standard geometrically thin accretion disk model and with using the results of the polarimetric observations. The p… ▽ More We determined the spin value of supermassive black hole (SMBH) in active galactic nuclei (AGN) with investigated ultraviolet-to-optical spectral energy distribution, presented in the sample of Shang et al. (2005). The estimates of the spin values have been produced at the base of the standard geometrically thin accretion disk model and with using the results of the polarimetric observations. The polarimetric observations are very important for determining the inclination angle of AGN disk. We presented the results of our determinations of the radiation efficiency of the accretion flow and values of the spins of SMBHs, that derives the coefficient of radiation efficiency. The majority of SMBHs of AGNs from Shang et al. (2005) sample are to be the Kerr black holes with the high spin value. △ Less

Submitted 20 November, 2017; originally announced November 2017.

Comments: 5 pages, 1 figure

Constraining Recoiling Velocities of Black Holes Ejected by Gravitational Radiation in Galaxy Mergers

Authors: M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili, S. D. Buliga

Abstract: Recent general relativistic simulations have shown that the coalescence of two spinning black holes (BH) can lead to recoiling speeds of the BH remnant of up to thousands of km/s as a result of the gravitational radiation emission. It is important that the accretion disc remains bound to ejected BH within the region where the gas orbital velocity is larger than the ejection speed. We considered th… ▽ More Recent general relativistic simulations have shown that the coalescence of two spinning black holes (BH) can lead to recoiling speeds of the BH remnant of up to thousands of km/s as a result of the gravitational radiation emission. It is important that the accretion disc remains bound to ejected BH within the region where the gas orbital velocity is larger than the ejection speed. We considered the situation when the recoiling kick radius coincides with the radius of the broad line region (BLR). We show that in this situation the observed polarization data of accretion disk emission allow to determine the value of the recoil velocity. We present the estimates of the kick velocity for AGN with determined polarization data. △ Less

Submitted 5 May, 2017; originally announced May 2017.

Comments: 7 pages, 1 figures, 2 tables. Accepted for publication in Astrophysics and Space Sciences

Polarization of broad line emission from AGNs with determined virial factors

Authors: M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili, S. D. Buliga

Abstract: We calculated the polarization degree of hydrogen Balmer broad emission lines from a number of active galactic nuclei (AGNs) with determined virial factors. The objects were selected from the sample presented by Decarli et al.(2008). In our calculations, we used the model of the flattened disc-like structure of the broad-line emission region (BLR). In this model, the expression for the virial fact… ▽ More We calculated the polarization degree of hydrogen Balmer broad emission lines from a number of active galactic nuclei (AGNs) with determined virial factors. The objects were selected from the sample presented by Decarli et al.(2008). In our calculations, we used the model of the flattened disc-like structure of the broad-line emission region (BLR). In this model, the expression for the virial factor makes it possible to determine the inclination angle for the flattened BLR, which in turn yields the polarization degree of the broad emission lines. As a result, we obtained the direct relation between the polarization degree and the virial factor. We also compared the determined values of the polarization degree with those obtained in polarimetric observations. △ Less

Submitted 24 March, 2017; originally announced March 2017.

Comments: 5 pages, 1 figure. Accepted for publication in MNRAS

New mechanism of radiation polarization in Seyfert-1 AGNs

Authors: N. A. Silant'ev, Yu. N. Gnedin, M. Yu. Piotrovich, T. M. Natsvlishvili, S. D. Buliga

Abstract: In most of Seyfert-1 active galactic nucei (AGN) the optical linear continuum polarization degree is usually small (less than 1%) and the polarization position angle is nearly parallel to the AGN radio-axis. However, there are many types-1 AGNs with unexplained intermediate values for both positional angles and polarization degrees. Our explanation of polarization degree and positional angle of Se… ▽ More In most of Seyfert-1 active galactic nucei (AGN) the optical linear continuum polarization degree is usually small (less than 1%) and the polarization position angle is nearly parallel to the AGN radio-axis. However, there are many types-1 AGNs with unexplained intermediate values for both positional angles and polarization degrees. Our explanation of polarization degree and positional angle of Seyfert-1 AGNs focuses on the reflection of non-polarized radiation from sub-parsec jets in optically thick accretion discs. The presence of a magnetic field surrounding the scattering media will induce Faraday rotation of the polarization plane that may explain the intermediate values of positional angles if there is a magnetic field component normal to the accretion disc. The Faraday rotation depolarization effect in disc diminishes the competition between polarization of the reflected radiation with the parallel component of polarization and the perpendicular polarization from internal radiation of disc (the Milne problem) in favor of polarization of reflected radiation. This effect allows us to explain the observed polarization of Seyfert-1 AGN radiation even though the jet optical luminosity is much lower than the luminosity of disc. We present the calculation of polarization degrees for a number of Seyfert-1 AGNs. △ Less

Submitted 29 June, 2016; originally announced June 2016.

Comments: 10 pages, 4 figures

A Polarimetric Method for Measuring Black Hole Masses in Active Galactic Nuclei

Authors: M. Yu. Piotrovich, Yu. N. Gnedin, N. A. Silant'ev, T. M. Natsvlishvili, S. D. Buliga

Abstract: The structure of the broad emission line region (BLR) in active galactic nuclei (AGN) remains unclear. We test in this paper a flattened configuration model for BLR. The virial theorem, by taking into account the disc shape of BLR, allows us to get a direct connection between the mass of a supermassive black hole (SMBH) and the inclination angle of the accretion flow. The inclination angle itself… ▽ More The structure of the broad emission line region (BLR) in active galactic nuclei (AGN) remains unclear. We test in this paper a flattened configuration model for BLR. The virial theorem, by taking into account the disc shape of BLR, allows us to get a direct connection between the mass of a supermassive black hole (SMBH) and the inclination angle of the accretion flow. The inclination angle itself is derived from the spectropolarimetric data on broad emission lines using the theory for the generation of polarized radiation developed by Sobolev and Chandrasekhar. As the result, the new estimates of SMBH masses in AGN with measured polarization of BLR are presented. It is crucial that the polarimetric data allow also to determine the value of the virial coefficient that is essential for determining SMBH masses. △ Less

Submitted 3 September, 2015; originally announced September 2015.

Comments: 5 pages

Magnetic field and radius of innermost stable circular orbit near SMBH in AGNs

Authors: M. Yu. Piotrovich, Yu. N. Gnedin, N. A. Silant'ev, T. M. Natsvlishvili, S. D. Buliga

Abstract: Magnetic fields in an accretion disk around the central black hole can modify the position of the innermost stable circular orbit (ISCO) radius and produces the difference for the classical Novikov-Thorne radius. We estimated the ISCO magnetic field strength on the base of polarimetric observations of the accretion disk radiation. This estimate can be obtained with taking into account the effect o… ▽ More Magnetic fields in an accretion disk around the central black hole can modify the position of the innermost stable circular orbit (ISCO) radius and produces the difference for the classical Novikov-Thorne radius. We estimated the ISCO magnetic field strength on the base of polarimetric observations of the accretion disk radiation. This estimate can be obtained with taking into account the effect of Faraday rotation of the polarization plane at the length of the free path of photon between successive electron scattering events. In a result we presented the new method for real estimation of the ISCO radius in the accretion disk, i.e. in the nearest vicinity of a central black hole. Our estimations confirmed the V.P. Frolov, A.A. Shoom and C. Tzounis (2014) conclusion that magnetic field produces the effect in a result of which the innermost stable circular orbit becomes closer to the horizon of a black hole. △ Less

Submitted 24 April, 2015; v1 submitted 7 October, 2014; originally announced October 2014.

Comments: 7 pages

Magnetic Fields of Compact Objects in Close X-Ray Binary Systems

Authors: M. Yu. Piotrovich, Yu. N. Gnedin, S. D. Buliga, T. M. Natsvlishvili, N. A. Silant'ev, A. S. Nikitenko

Abstract: X-ray binary systems are very popular objects for astrophysical investigations. Compact objects in these systems are neutron stars, white dwarfs and black holes. Neutron stars and white dwarfs can have intrinsic magnetic fields. There is well known, famous theorem about absence of intrinsic magnetic fields of black holes. But magnetic field can exist in the accretion disk around a black hole. We p… ▽ More X-ray binary systems are very popular objects for astrophysical investigations. Compact objects in these systems are neutron stars, white dwarfs and black holes. Neutron stars and white dwarfs can have intrinsic magnetic fields. There is well known, famous theorem about absence of intrinsic magnetic fields of black holes. But magnetic field can exist in the accretion disk around a black hole. We present here the real estimates of the magnetic field strength at the radius of innermost stable orbit in an accretion disk of stellar mass black holes. △ Less

Submitted 8 September, 2014; originally announced September 2014.

Comments: 4 pages

Magnetic fields of active galactic nuclei and quasars with polarized broad H-alpha lines

Authors: N. A. Silant'ev, Yu. N. Gnedin, S. D. Buliga, M. Yu. Piotrovich, T. M. Natsvlishvili

Abstract: We present estimates of magnetic field in a number of AGNs from the Spectropolarimetric atlas of Smith, Young & Robinson (2002) from the observed degrees of linear polarization and the positional angles of spectral lines (H-alpha) (broad line regions of AGNs) and nearby continuum. The observed polarization is lower than the Milne value in a non-magnetized atmosphere. We hypothesize that the polari… ▽ More We present estimates of magnetic field in a number of AGNs from the Spectropolarimetric atlas of Smith, Young & Robinson (2002) from the observed degrees of linear polarization and the positional angles of spectral lines (H-alpha) (broad line regions of AGNs) and nearby continuum. The observed polarization is lower than the Milne value in a non-magnetized atmosphere. We hypothesize that the polarized radiation escapes from optically thick magnetized accretion discs and is weakened by the Faraday rotation effect. This effect is able to explain both the value of the polarization and the position angle. We estimate the required magnetic field in the broad line region by using simple asymptotic analytical formulas for Milne's problem in magnetized atmosphere, which take into account the last scattering of radiation before escaping from the accretion disc. The polarization of a broad spectral line escaping from disc is described by the same mechanism. The characteristic features of polarization of a broad line is the minimum of the degree of polarization in the center of the line and continuous rotation of the position angle from one wing to another. These effects can be explained by existence of clouds in the left (velocity is directed to an observer) and the right (velocity is directed from an observer) parts of the orbit in a rotating keplerian magnetized accretion disc. The base of explanation is existence of azimuthal magnetic field in the orbit. The existence of normal component of magnetic field makes the picture of polarization asymmetric. The existence of clouds in left and right parts of the orbit with different emissions also give the contribution in asymmetry effect. Assuming a power-law dependence of the magnetic field inside the disc, we obtain the estimate of the magnetic field strength at first stable orbit near the central SMBH for a number of AGNs. △ Less

Submitted 13 March, 2012; originally announced March 2012.

Comments: 15 pages, 4 figures

Black holes of intermediate masses in globular clusters: constraints on a spin of a black hole

Authors: S. D. Buliga, V. I. Globina, Yu. N. Gnedin, T. M. Natsvlishvili, M. Yu. Piotrovich, N. A. Shaht

Abstract: In this paper we determined values of a spin of central black holes of the intermediate masses in globular clusters. For determination of value of a spin we used the known relation between the kinetic power of the relativistic jet and observable radio-luminosity of the region near to a central black hole, and our estimates have based on the known Blandford-Znajek mechanism. The value of a magnetic… ▽ More In this paper we determined values of a spin of central black holes of the intermediate masses in globular clusters. For determination of value of a spin we used the known relation between the kinetic power of the relativistic jet and observable radio-luminosity of the region near to a central black hole, and our estimates have based on the known Blandford-Znajek mechanism. The value of a magnetic field strength near the event horizon of a black hole was derived via magnetic coupling mechanism. Accretion rate was derived using Bondi-Hoyle mechanism. △ Less

Submitted 30 July, 2011; originally announced August 2011.

Comments: 4 pages

Spectropolarimetric Observations of Active Galactic Nuclei with the 6-m BTA Telescope

Authors: V. L. Afanasiev, N. V. Borisov, Yu. N. Gnedin, T. M. Natsvlishvili, M. Yu. Piotrovich, S. D. Buliga

Abstract: 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… ▽ More 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. △ Less

Submitted 19 April, 2011; originally announced April 2011.

Comments: 10 pages, 2 figures

Journal ref: Astronomy Letters, 2011, Vol.37, No.5, pp.302-310

Polarization of AGN in UV Spectral Range

Authors: Yu. N. Gnedin, M. Yu. Piotrovich, T. M. Natsvlishvili

Abstract: We present the review of some new problems in cosmology and physics of stars in connection with future launching of WSO. We discuss three problems. UV observations of distant z > 6 quasars allow to obtain information on the soft < 1 KeV X-ray radiation of the accretion disk around a supermassive black hole because of its cosmological redshift. Really the region of X-ray radiation is insufficiently… ▽ More We present the review of some new problems in cosmology and physics of stars in connection with future launching of WSO. We discuss three problems. UV observations of distant z > 6 quasars allow to obtain information on the soft < 1 KeV X-ray radiation of the accretion disk around a supermassive black hole because of its cosmological redshift. Really the region of X-ray radiation is insufficiently investigated because of high galactic absorption. In a result one will get important information on the reionization zone of the Universe. Astronomers from ESO revealed the effect of alignment of electric vectors of polarized QSOs. One of the probable mechanism of such alignment is the conversion of QSO radiation into low mass pseudoscalar particles (axions) in the extragalactic magnetic field. These boson like particles have been predicted by new SUSY particle physics theory. Since the probability of such conversion is increasing namely in UV spectral range one can expect the strong correlation between UV spectral energy distribution of QSO radiation and polarimetric data in the optical range. In the stellar physics one of the interesting problems is the origin of the X-ray sources with super Eddington luminosities. The results of UV observations of these X-ray sources will allow to find the origin of these sources as accreting intermediate mass black holes. △ Less

Submitted 8 March, 2011; originally announced March 2011.

Comments: 6 pages, 3 figures

Dependence of linear polarization of radiation in accretion disks on the spin of central black hole

Authors: N. A. Silant'ev, M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili

Abstract: We suppose that linear optical polarization is due to multiple scattering in optically thick magnetized accretion disk around central black hole. The polarization degree is very sensitive to the spin of black hole - for Kerr rotating hole the polarization is higher than for Schwarzschild non-rotating one if both holes have the same luminosities and masses. The reason of this effect is that the rad… ▽ More We suppose that linear optical polarization is due to multiple scattering in optically thick magnetized accretion disk around central black hole. The polarization degree is very sensitive to the spin of black hole - for Kerr rotating hole the polarization is higher than for Schwarzschild non-rotating one if both holes have the same luminosities and masses. The reason of this effect is that the radius of the first stable orbit for non-rotating hole is equal to three gravitational radiuses, and for fast rotating Kerr hole is approximately 6 times lesser. Magnetic field, decreasing from first stable orbits, is much larger in the region of escaping of optical radiation for the case of Schwarzschild hole than for Kerr one. Large magnetic field gives rise to large depolarization of radiation due to Faraday rotation effect. This explains the mentioned result. It seems that the ensemble of objects with observed polarization mostly consists of Kerr black holes. △ Less

Submitted 9 November, 2010; originally announced November 2010.

Comments: 7 pages

Magnetic Fields of Black Holes and the Variability Plane

Authors: M. Yu. Piotrovich, N. A. Silant'ev, Yu. N. Gnedin, T. M. Natsvlishvili

Abstract: We estimated the magnetic field strength at the horizon radius of black holes, that is derived by the magnetic coupling process and depended on the black hole mass $M_{BH}$ and the accretion rate $\dot{M}$. Our estimation is based on the use of the fundamental variability plane for stellar mass black holes, AGNs and QSOs. The typical values of magnetic field strength on the black hole horizon ar… ▽ More We estimated the magnetic field strength at the horizon radius of black holes, that is derived by the magnetic coupling process and depended on the black hole mass $M_{BH}$ and the accretion rate $\dot{M}$. Our estimation is based on the use of the fundamental variability plane for stellar mass black holes, AGNs and QSOs. The typical values of magnetic field strength on the black hole horizon are appeared at the level of $B_{BH}\sim 10^8$G for stellar mass black holes and $B_{BH}\sim 10^4$G for the supermassive black holes. We have obtained the relation $p_l\sim ν^{-1/2}_b$ between the intrinsic polarization of the accretion disk radiation and the characteristic frequency of the black hole X-ray variability. △ Less

Submitted 26 February, 2010; originally announced February 2010.

Comments: 4 pages

Intrinsic Origin Of Extreme-Scale Rotation Of Quasar Polarization Vectors

Authors: N. A. Silant'ev, M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili

Abstract: Extreme-scale alignment of quasar optical polarization vectors at cosmological scales ($z\le 2$) is also characterized by the rotation of mean position angle $χ$ with $Δχ\approx 30^{\circ}$ per 1 Gpc. For observing interval of $z$ the total rotation angle acquires the value $\sim 90^{\circ}$. We suggest the possible explanation of the half of this rotation as a consequence of physical transforma… ▽ More Extreme-scale alignment of quasar optical polarization vectors at cosmological scales ($z\le 2$) is also characterized by the rotation of mean position angle $χ$ with $Δχ\approx 30^{\circ}$ per 1 Gpc. For observing interval of $z$ the total rotation angle acquires the value $\sim 90^{\circ}$. We suggest the possible explanation of the half of this rotation as a consequence of physical transformation of initially vertical magnetic field ${\bf B}_{\|}$, directed along the normal ${\bf N}$ to the surface of accretion disk, into the horizontal (perpendicular to ${\bf N}$) one. We found asymptotical analytical expressions for axially averaged polarization degree $p$ and mean position angle $χ$ for various types of magnetized accretion disks. We found also that during the evolution can be realized the case $B_{\bot}\approx B_{\|}$ where position angle $χ$ rotates from $45^{\circ}$ to zero. This rotation may occur during fairly great cosmological time (corresponding to $Δz\sim 1-2$). The part of rotation $\sim Δχ\approx 45^{\circ}$ can be explained by a mechanism of alignment of polarization vectors, say distribution of the part of quasars as a spiral in the cosmic space with slow variation of rotation axis of corresponding accretion disks. Both mechanisms are mutually related one with another. △ Less

Submitted 14 November, 2009; originally announced November 2009.

Comments: 7 pages

Magnetic Fields of Agns and Standard Accretion Disk Model: Testing by Optical Polarimetry

Authors: N. A. Silant'ev, M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili

Abstract: We have developed the method that allows us to estimate the magnetic field strength at the horizon of a supermassive black hole (SMBH) through the observed polarization of optical emission of the accreting disk surrounding SMBH. The known asymptotic formulae for the Stokes parameters of outgoing radiation are azimuthal averaged, which corresponds to an observation of the disk as a whole. We cons… ▽ More We have developed the method that allows us to estimate the magnetic field strength at the horizon of a supermassive black hole (SMBH) through the observed polarization of optical emission of the accreting disk surrounding SMBH. The known asymptotic formulae for the Stokes parameters of outgoing radiation are azimuthal averaged, which corresponds to an observation of the disk as a whole. We consider two models of the embedding 3D-magnetic field, the regular field, and the regular field with an additional chaotic (turbulent) component. It is shown that the second model is preferable for estimating the magnetic field in NGC 4258. For estimations we used the standard accretion disk model assuming that the same power-law dependence of the magnetic field follows from the range of the optical emission down to the horizon. The observed optical polarization from NGC 4258 allowed us to find the values 10^3 - 10^4 Gauss at the horizon, depending on the particular choice of the model parameters. We also discuss the wavelength dependencies of the light polarization, and possibly applying them for a more realistic choice of accretion disk parameters. △ Less

Submitted 7 September, 2009; originally announced September 2009.

Comments: 14 pages, 2 figures

The Black Hole Mass and Magnetic Field Correlation in AGN: Testing by Optical Polarimetry

Authors: N. A. Silant'ev, M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili

Abstract: We consider the integral light polarization from optically thick accretion disks. Basic mechanism is the multiple light scattering on free electrons (Milne's problem) in magnetized atmosphere. The Faraday rotation of the polarization plane changes both the value of integral polarization degree $p$ and the position angle $χ$. Besides, the characteristic spectra of these values appear. We are test… ▽ More We consider the integral light polarization from optically thick accretion disks. Basic mechanism is the multiple light scattering on free electrons (Milne's problem) in magnetized atmosphere. The Faraday rotation of the polarization plane changes both the value of integral polarization degree $p$ and the position angle $χ$. Besides, the characteristic spectra of these values appear. We are testing the known relation between magnetic field of black hole at the horizon $B_{BH}$ and its mass $M_{BH}$, and the usual power-law distribution inside the accretion disk. The formulae for $p(λ)$ and $χ(λ)$ depend on a number of parameters describing the particular dependence of magnetic field in accretion disk (the index of power-law distribution, the spin of the black hole, etc.). Comparison of our theoretical values of $p$ and $χ$ with observed polarization can help us to choice more realistic values of parameters if the accretion disk mechanism gives the main contribution to the observed integral polarization. The main content is connected with estimation of validity of the relation between $B_{BH}$ and $M_{BH}$. We found for the AGN NGC 4258 that such procedure does not confirm the mentioned correlation between magnetic field and mass of black hole. △ Less

Submitted 19 August, 2009; originally announced August 2009.

Comments: 7 pages

Magnetic Fields of Nearby Active Galactic Nuclei and Correlation of the Highest-Energy Cosmic Rays with their Positions

Authors: M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili

Abstract: The correlation between the pointing direction of ultra high energy cosmic rays and AGN observed by the Pierre Auger Collaboration is explained in the framework of acceleration process in AGN. This acceleration process is produced by a rotating accretion disk around a black hole that is frozen-in magnetic field. In a result the accretion disk is acting as a induction accelerator of cosmic rays.… ▽ More The correlation between the pointing direction of ultra high energy cosmic rays and AGN observed by the Pierre Auger Collaboration is explained in the framework of acceleration process in AGN. This acceleration process is produced by a rotating accretion disk around a black hole that is frozen-in magnetic field. In a result the accretion disk is acting as a induction accelerator of cosmic rays. We estimate the resulting magnetic field in the framework of the magnetic coupling process. The results of our calculations allow to make the conclusion that the Flat Spectrum Radio Quasars appear the effective cosmic accelerators. We estimate also the attenuation of highest-energy cosmic rays in a result of their interaction with ambient radiation field. △ Less

Submitted 20 November, 2008; originally announced November 2008.

Comments: 5 pages

Photon-Axion-Like Particle Coupling Constant and Cosmological Observations

Authors: M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili

Abstract: We estimated the photon-pseudoscalar particle mixing constant from the effect of cosmological alignment and cosmological rotation of polarization plane of distant QSOs. This effect is explained in terms of birefringent phenomenon due to photon-pseudoscalar (axion-like) particle mixing in a cosmic magnetic field. On the contrary, one can estimate the strength of the cosmic magnetic field using th… ▽ More We estimated the photon-pseudoscalar particle mixing constant from the effect of cosmological alignment and cosmological rotation of polarization plane of distant QSOs. This effect is explained in terms of birefringent phenomenon due to photon-pseudoscalar (axion-like) particle mixing in a cosmic magnetic field. On the contrary, one can estimate the strength of the cosmic magnetic field using the constraints on the photon-axion-like particle coupling constant from the CAST experiment and from SNe Ia dimming effect. In a result, the lower limit on the intergalactic ($z\approx 1÷2$) magnetic field appears at the level of about $4\times 10^{-10}÷10^{-11}$ G. △ Less

Submitted 23 May, 2008; originally announced May 2008.

Comments: 8 pages

Synchrotron Self-Absorption Process in GRBs and the Isotropic Energy - Peak Energy Fundamental Relation

Authors: M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili

Abstract: The existence of strong correlation between the peak luminosity (and/or bolometric energetics) of Gamma Ray Bursts (GRB) is one of the most intrigue problem of GRB physics. This correlation is not yet understood. Here we demonstrate that this correlation can be explained in framework of synchrotron self-absorption (SSA) mechanism of GRB prompt emission. We estimate the magnetic field strength of… ▽ More The existence of strong correlation between the peak luminosity (and/or bolometric energetics) of Gamma Ray Bursts (GRB) is one of the most intrigue problem of GRB physics. This correlation is not yet understood. Here we demonstrate that this correlation can be explained in framework of synchrotron self-absorption (SSA) mechanism of GRB prompt emission. We estimate the magnetic field strength of the central engine at the level $B\sim 10^{14} (10^3/Γ)^3 (1+z)^2$, where $Γ$ is the Lorentz factor of fireball. △ Less

Submitted 21 August, 2007; originally announced August 2007.

Comments: 5 pages

PVLAS Experiment: Some Astrophysical Consequences

Authors: Yu. N. Gnedin, M. Yu. Piotrovich, T. M. Natsvlishvili

Abstract: The birefringent effects of photon-pseudoscalar boson (Goldstone) particle mixing in intergalactic magnetic field are calculated for cosmological objects. We use the recent results of PVLAS collaboration that reported recently the observation of a rotation of the polarization plane of light propagating through a transverse static magnetic field. Such results which were interpretated as arising d… ▽ More The birefringent effects of photon-pseudoscalar boson (Goldstone) particle mixing in intergalactic magnetic field are calculated for cosmological objects. We use the recent results of PVLAS collaboration that reported recently the observation of a rotation of the polarization plane of light propagating through a transverse static magnetic field. Such results which were interpretated as arising due to conversion of photon into pseudoscalar with coupling strength $g_{aγ}\sim 4\times 10^{-6} GeV^{-1}$ allows us to estimate the intergalactic magnetic field magnitude as $\sim 10^{-16} G$ based on Hatsemekers et al. observations of extreme-scale alignments of quasar polarization vectors. We have analyzed some additional results of astronomical observations that could be explained by axion interpretation of the PVLAS data: a sharp steepening of the QSO continuum short ward of $\simeq 1100$Å, observed circular polarization of AGNs and QSOs, discrepancy between observed intrinsic polarization of stars in the Local Bubble and stellar spectral classification. The observed polarization of stars in the Local Bubble can't be explained by interstellar origin. △ Less

Submitted 13 July, 2006; originally announced July 2006.

Journal ref: Mon.Not.Roy.Astron.Soc.374:276-281,2007

Magnetic fields of active galaxy nuclei and cosmological models

Authors: Yu. N. Gnedin, T. M. Natsvlishvili, M. Yu. Piotrovich

Abstract: We present the review of various methods of detection of magnetic field strengths in the nearest regions of the active galaxy nuclei (AGN) which are the high energetic machines. Original spectropolarimetric method developed in the Pulkovo Observatory allows us to determine the magnitude and geometry of the magnetic field in the region of the optical and more hard electromagnetic radiation. The r… ▽ More We present the review of various methods of detection of magnetic field strengths in the nearest regions of the active galaxy nuclei (AGN) which are the high energetic machines. Original spectropolarimetric method developed in the Pulkovo Observatory allows us to determine the magnitude and geometry of the magnetic field in the region of the optical and more hard electromagnetic radiation. The results of theoretical calculations are compared to the results of spectropolarimetric observations of AGN. We used the method of determining magnetic fields through the spectrum synchrotron radiation in the region of synchrotron self-absorption. As the magnitude of magnetic field of the extragalactic source depends very strongly on the angular size of extragalactic source and therefore on the photometric distance the calculated magnetic field magnitudes depends very strongly on the definite cosmological model. This result allows us to present the new method for determination of the most important cosmological parameters including dark matter and dark energy parameters. △ Less

Submitted 15 September, 2005; originally announced September 2005.

Comments: 8 pages, 7 figures

Journal ref: Grav.Cosmol.11:333-339,2005

Spectropolarimetry and Infrared Photometry of Magnetic White Dwarfs: Vacuum Polarization Effect or Magnetic CIA?

Authors: Yu. N. Gnedin, N. V. Borisov, V. M. Larionov, I. D. Naidenov, T. M. Natsvlishvili, M. Yu. Piotrovich

Abstract: We present brief review of two probable physical mechanisms that can explain the results of photometric and spectropolarimetric observations of magnetic white dwarfs: vacuum polarization effect into a strong magnetic field and, so-called, magnetic collision induced absorption (magnetic CIA). Both mechanisms provide observed rotation of polarization ellipse and suppression of spectral energy dist… ▽ More We present brief review of two probable physical mechanisms that can explain the results of photometric and spectropolarimetric observations of magnetic white dwarfs: vacuum polarization effect into a strong magnetic field and, so-called, magnetic collision induced absorption (magnetic CIA). Both mechanisms provide observed rotation of polarization ellipse and suppression of spectral energy distributions. The results of spectropolarimetric observations of magnetic white dwarfs made at Russian BTA-6m and the results of the near infrared photometric observations with Russian-Italian AZT-24 telescope located at Campo Imperatore are also presented. △ Less

Submitted 7 September, 2004; originally announced September 2004.

Comments: 13 pages, 4 figures

The polarization effects of radiation from magnetized envelopes and extended accretion structures

Authors: Yu. N. Gnedin, N. A. Silant'ev, M. Yu. Piotrovich, M. A. Pogodin

Abstract: The results of numerical calculations of linear polarization from magnetized spherical optically thick and optically thin envelopes are presented. We give the methods how to distinguish magnetized optically thin envelopes from optically thick ones using observed spectral distributions of the polarization degree and the positional angle. The results of numerical calculations are used for analysis… ▽ More The results of numerical calculations of linear polarization from magnetized spherical optically thick and optically thin envelopes are presented. We give the methods how to distinguish magnetized optically thin envelopes from optically thick ones using observed spectral distributions of the polarization degree and the positional angle. The results of numerical calculations are used for analysis of polarimetric observations of OB and WR stars, X-ray binaries with black hole candidates (Cyg X-1, SS 433) and supernovae. The developed method allows to estimate magnetic field strength for the objects mentioned above. △ Less

Submitted 16 June, 2004; v1 submitted 11 June, 2004; originally announced June 2004.

Comments: 18 pages, 6 figures

Magnetic and Electric Fields around the Black Hole in Cyg X-1

Authors: Yu. N. Gnedin, N. V. Borisov, T. M. Natsvlishvili, M. Yu. Piotrovich, N. A. Silant'ev

Abstract: Analysis of polarimetric observations of X-ray binary Cyg X-1/HDE 226868 including the data obtained by BTA-6m allows to estimate the magnetic field magnitude near the inner radius of the accretion disk. The magnetic field magnitude occurred to be $\sim 10^{8}$ G. For power law of radial dependence of magnetic field into an accretion disk we estimates the value of an index of power law. For the… ▽ More Analysis of polarimetric observations of X-ray binary Cyg X-1/HDE 226868 including the data obtained by BTA-6m allows to estimate the magnetic field magnitude near the inner radius of the accretion disk. The magnetic field magnitude occurred to be $\sim 10^{8}$ G. For power law of radial dependence of magnetic field into an accretion disk we estimates the value of an index of power law. For the Cyg X-1/HDE 226868 system the value of this index appears non less then two. If one accepts as a characteristic scale of a magnetic field generation region the dyadosphere radius, one can estimate the charge magnitude of a black hole. For Cyg X-1 this magnitude appears to be $\sim 0.01M\sqrt{G}$, where M is a black hole mass. △ Less

Submitted 9 April, 2003; originally announced April 2003.

Comments: 10 pages, 1 figure