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V. S. Beskin

Publications and source records attributed to V. S. Beskin.

At least 37 records · Page 2Linked to original sources
arXiv2019

M87 black hole mass and spin estimate through the position of the jet boundary shape break

We propose a new method of estimating a mass of a super massive black hole residing in the center of an active galaxy. The active galaxy M87 offers a convenient test case for the method due to the existence of a large amount of observational data on the jet and ambient environment properties in the central area of the object. We suggest that the observed transition of a jet boundary shape from a parabolic to a conical form is associated with the flow transiting from the magnetically dominated regime to the energy equipartition between plasma bulk motion and magnetic field. By coupling the unique set of observations available for the jet kinematics, environment and boundary profile with our MHD modelling under assumption on the presence of a dynamically important magnetic field in the M87 jet, we estimate the central black hole mass and spin. The method leads us to believe that the M87 super massive black hole has a mass somewhat larger than typically accepted so far.

astro-ph.HE↗
arXiv2018

Radio pulsars: already fifty years!

Although fifty years have passed since the discovery of radio pulsars, there is still no satisfactory understanding of how these amazing objects operate. While there has been significant progress in understanding the basic properties of radio pulsars, there is as yet no consensus on key issues, such as the nature of coherent radio emission or the conversion mechanism of the electromagnetic energy of the pulsar wind into particle energy. In this review, we present the main theoretical results on the magnetosphere of neutron stars. We formulate a number of apparently simple questions, which nevertheless remain unanswered since the very beginning of the field and which must be resolved before any further progress can be made.

astro-ph.HE↗
arXiv2017

On the internal structure of the current sheet in the pulsar wind

We investigate the internal structure of the current sheet in the pulsar wind within force-free and two-fluid MHD approximations. Within the force-free approximation we obtain general asymptotic solution of the Grad-Shafranov equation for quasi-spherical pulsar wind up to the second order in small parameter $\varepsilon = (Ωr/c)^{-1}$. The solution allows an arbitrary latitudinal structure of the radial magnetic field, including that obtained in the numerical simulations of oblique rotators. It is also shown that the shape of the current sheet does not depend on the latitudinal structure. For the internal region of the current sheet outside the fast magnetosonic surface where the force-free approximation is not valid we use two-fluid MHD approximation. Carrying out calculations in the comoving reference frame we succeed in determining intrinsic electric and magnetic fields of a sheet. It allows us to analyze time-dependent effects which were not investigated up to now. In particular, we estimate the efficiency of the particle acceleration inside the sheet. Finally, after investigating the motion of individual particles in the time-dependent current sheet, we find self-consistently the width of the sheet and its time evolution.

astro-ph.HE↗
arXiv2017

On the acceleration and deceleration of relativistic jets in active galactic nuclei - II. Mass-loading

The effect of a mass-loading of the magnetohydrodynamic (MHD) flow in a relativistic jet from active galactic nuclei (AGN) due to $γγ\rightarrow e^+e^-$ conversion is considered analytically. We argue that the effects of charge average separation due to specific initial pairs' motion lead to partial magnetic and electric fields screening or enhancement. The effect of the fields screening has not been considered earlier. The pairs with the center-of-mass moving faster or slower than the bulk plasma flow create a surface charge and a current which either screen or enhance both electric and magnetic fields in a pair creation domain. This impacts the bulk flow motion, which either accelerates or decelerates. The pairs with the center-of-mass moving with exactly the drift velocity does not induce the fields disturbance. In this case the flow decelerates due to pure mass-loading. For these different cases the Lorentz factor of the loaded outflow is calculated as a function of loading pairs number density. The effect may be important on sub-parsec to parsec scales due to conversion of TeV jet radiation on soft infra-red to ultra-violet external isotropic photon field. This leads to an outer shell acceleration. The conversion of MeV jet radiation on larger scales may account for the flow deceleration due to pure mass-loading. The proposed mechanism may be a source of internal shocks and instabilities in the pair creation region.

astro-ph.HE↗
arXiv2016

On the deceleration of relativistic jets in active galactic nuclei I: Radiation drag

Deceleration of relativistic jets from active galactic nuclei (AGNs) detected recently by MOJAVE team is discussed in connection with the interaction of the jet material with the external photon field. Appropriate energy density of the isotropic photon field which is necessary to decelerate jets is determined. It is shown that the disturbances of the electric potential and magnetic surfaces play important role in general dynamics of particle deceleration.

astro-ph.HE↗
arXiv2015

Radio Pulsars

Almost 50 years after radio pulsars were discovered in 1967, our understanding of these objects remains incomplete. On the one hand, within a few years it became clear that neutron star rotation gives rise to the extremely stable sequence of radio pulses, that the kinetic energy of rotation provides the reservoir of energy, and that electromagnetic fields are the braking mechanism. On the other hand, no consensus regarding the mechanism of coherent radio emission or the conversion of electromagnetic energy to particle energy yet exists. In this review, we report on three aspects of pulsar structure that have seen recent progress: the self-consistent theory of the magnetosphere of an oblique magnetic rotator; the location, geometry, and optics of radio emission; and evolution of the angle between spin and magnetic axes. These allow us to take the next step in understanding the physical nature of the pulsar activity.

astro-ph.HE↗
arXiv2014

Effect of Electromagnetic Pulse Transverse Inhomogeneity on the Ion Acceleration by Radiation Pressure

In the ion acceleration by radiation pressure a transverse inhomogeneity of the electromagnetic pulse results in the displacement of the irradiated target in the off-axis direction limiting achievable ion energy. This effect is described analytically within the framework of the thin foil target model and with the particle-in-cell simulations showing that the maximum energy of accelerated ions decreases while the displacement from the axis of the target initial position increases. The results obtained can be applied for optimization of the ion acceleration by the laser radiation pressure with the mass limited targets.

physics.plasm-ph↗
arXiv2014

Intrinsic Physical Conditions and Structure of Relativistic Jets in Active Galactic Nuclei

The analysis of the frequency dependence of the observed shift of the cores of relativistic jets in active galactic nuclei (AGN) allows us to evaluate the number density of the outflowing plasma n and, hence, the multiplicity parameter, which is a ratio of particle number density to Goldreich-Julian number density. We have obtained the median value for the multiplicity parameter to be 3x10^13 and the median value for the Michel magnetization parameter is 8 from an analysis of 97 sources. Since the magnetization parameter can be interpreted as the maximum possible Lorentz factor of the bulk motion which can be obtained for relativistic magnetohydrodynamic (MHD) flow, this estimate is in agreement with the observed superluminal motion of bright features in AGN jets. Moreover, knowing these key parameters, one can determine the transverse structure of the flow. We show that the poloidal magnetic field and particle number density are much larger in the center of the jet than near the at boundary. The MHD model can also explain the typical observed level of jet acceleration. Finally, casual connectivity of strongly collimated jets is discussed.

astro-ph.HE↗
arXiv2014

The Shapes of Pulsar Radio Pulses in the Plane of the Sky

The sizes of pulsar radio pulses in the plane of the sky are determined. This is important not only in relation to the possibility of directly resolving the radio pulses spatially, but also for verifying and placing constraints on existing theories of the radio emission. The shape of the pulse radio image and its variation as a function of the pulse phase for the extraordinary (X) and ordinary (O) modes are determined for the simple case of a dipolar magnetic field. Images are obtained for pulsars with various angles between their magnetic and rotational axes, and also for various model parameters, such as the height of the emission, the size of the emission region as a function of the height, and the Lorentz factor of the secondary plasma. It is shown that the size of the resulting image is appreciably smaller at the center of the pulse than at its edges.

astro-ph.HE↗
arXiv2014

On the spherically-symmetric turbulent accretion

We analize the quasi-spherical accretion in the presence of axisymmetric vortex turbulence. It is shown that in this case the turbulence changes mainly the effective gravity potential but not the effective pressure.

astro-ph.HE↗
arXiv2014

Effects of the Angular Momentum of Accreting Matter on the Flow Structure in the Subsonic Settling and Bondi-Hoyle Accretion Regimes

Previously unexplored accretion regimes associated with the rotation of accreting matter, namely the perturbations of a quasi-spherical subsonic settling flow and Bondi-Hoyle accretion in the presence of axial rotation, are considered within the framework of ideal hydrodynamics. For subsonic settling accretion, the perturbations are shown to grow rapidly as the gravitating center is approached, so that the flow in the inner regions can no longer be considered as quasi-spherical. For Bondi-Hoyle accretion, a vacuum cylindrical cavity is shown to be formed at large distances from the gravitating center near the flow axis, with the flow velocity outside this cavity being virtually independent of the distance to the rotation axis.

astro-ph.HE↗
arXiv2013

Radio pulsars: the search for truth

It was as early as the 1980s that A V Gurevich and his group proposed a theory to explain the magnetosphere of radio pulsars and the mechanism by which they produce coherent radio emission. The theory has been sharply criticized and is currently rarely mentioned when discussing the observational properties of radio pulsars, even though all the criticisms were in their time disproven in a most thorough and detailed manner. Recent results show even more conclusively that the theory has no internal inconsistencies. New observational data also demonstrate the validity of the basic conclusions of the theory. Based on the latest results on the effects of wave propagation in the magnetosphere of a neuron star, we show that the developed theory does indeed allow quantitative predictions of the evolution of neutron stars and the properties of the observed radio emission.

astro-ph.HE↗
arXiv2013

On the structure of the magnetic field near a black hole in active galactic nuclei

Using the Grad-Shafranov equation, we consider a new analytical model of the black hole magnetosphere based on the assumption that the magnetic field is radial near the horizon and uniform (cylindrical) in the jet region. Within this model, we have managed to show that the angular velocity of particles near the rotation axis of the black hole can be smaller than one half of the black hole angular velocity. This result is consistent with the latest numerical simulations.

astro-ph.HE↗
arXiv2012

On the mean profiles of radio pulsars I: Theory of the propagation effects

We study the influence of the propagation effects on the mean profiles of radio pulsars using the Kravtsov-Orlov method of the wave propagation in the inhomogeneous media. This approach allows us firstly to include into consideration the transition from geometrical optics to vacuum propagation, the cyclotron absorption, and the wave refraction simultaneously. In addition, arbitrary non-dipole magnetic field configuration, drift motion of plasma particles, and their realistic energy distribution are taken into account. The one-to-one correspondence between the signs of circular polarization and position angle (p.a.) derivative along the profile for both ordinary and extraordinary waves is predicted. Using the numerical integration we now can model the main profiles of radio pulsars. It is shown that standard S-shape form of the p.a. swing can be realized for small enough pair production multiplicity and large enough bulk plasma Lorentz factor only. It is also shown that the value of p.a. maximum derivative, that is often used for determination the angle between magnetic dipole and rotation axis, depends on the plasma parameters and could differ from the rotation vector model (RVM) prediction.

astro-ph.HE↗
arXiv2011

On the collective curvature radiation

The paper deals with the one possible mechanism of the pulsar radio emission, i.e., with the collective curvature radiation of the relativistic particle stream moving along the curved magnetospheric magnetic field lines. It is shown that the electromagnetic wave containing one cylindrical harmonic exp{isϕ} can not be radiated by the curvature radiation mechanism, that corresponds to radiation of a charged particle moving along curved magnetic field lines. The point is that the particle in vacuum radiates the triplex of harmonics (s, s \pm 1), so for the collective curvature radiation the wave polarization is very important and cannot be fixed a priori. For this reason the polarization of real unstable waves must be determined directly from the solution of wave equations for the media. Its electromagnetic properties should be described by the dielectric permittivity tensor \^ε(ω,k,r), that contains the information on the reaction on all possible types of radiation.

astro-ph.HE↗
arXiv2011

Determination of a magnetization parameter of the parsec-scale AGN jets

The observed shift of the core of the relativistic AGN jets as a function of frequency allows us to evaluate the number density of outflowing plasma and, hence, the magnetization parameter. New analysis of more than 20 sources shows that for most of jets the magnetization parameter ~ 10 - 100. Since the magnetization parameter is the maximum possible bulk Lorentz-factor of the relativistic flow, this estimate is consistent with the observed superluminal motion.

astro-ph.HE↗