arXiv subjects

Ya. N. Istomin

Publications and source records attributed to Ya. N. Istomin.

At least 19 recordsLinked to original sources

arXiv2023

Surfatron acceleration of the high energy protons in the relativistic jets

This paper describes the acceleration of high energies protons captured by electrostatic waves in the frame of jet arising in the area of instability of relativistic jet, where spiral structures are excited. The wave has a spatially heterogeneous structure of $\exp(i k_\parallel z +i m_ϕϕ)$. Protons can be captured in potential wells created by spiral waves, and thereby experience acceleration with a mechanism known as surfatron acceleration. Expressions of the maximum energy ($ E_p \simeq 10^{19} eV $) and the energy spectrum from jet parameters are obtained.

astro-ph.HE↗

arXiv2020

Acoustic $α$-disk

It is shown that the turbulent flow of acoustic waves propagating outward from the inner edge of the disk causes the accretion of the matter onto the center. The exponential amplification of waves takes place in the resonance region, $ ω= (n\pm 1)Ω$. Here $ ω$ is the frequency of the acoustic wave, $ n $ is its azimuthal wave number, $ Ω(r) $ is the angular frequency of rotation of the disk. The effect is similar to the inverse Landau damping in a collisionless plasma. Energy comes from the energy of rotation of the disk. That leads to decrease of the disk angular momentum and to accretion of the matter. The value of the accretion rate $dM/dt$ is ${\dot M} = πrc_s Σ_0 (c_s / v_{ϕ0})^2 W $. Here $ c_s $ is the speed of sound of the disk gas, $ v_{ϕ0} $ is the Keplerian rotation velocity, $Σ_0 $ is the surface density of the disk, $ W $ is total power of the acoustic turbulence, $ W \simeq \int_0^\infty d ω\sum_{n\geq 0} \Big {|} \frac {Σ'} {Σ_0} \Big {|}^2 (ω, n) $, $ |Σ'|^2 (ω, n) $ is the spectral power of turbulence. The presented picture of accretion is consistent with the observed variations of X-ray and optical radiation from objects whose activity is associated with accretion of gas onto them.

physics.plasm-ph↗

arXiv2020

Acceleration of high energy protons in AGN relativistic jets

In this paper, we investigate the acceleration in relativistic jets of high-energy proton preaccelerated in the magnetosphere of a supermassive black hole. The proton reaches maximum energy when passing the total potential difference of $U$ between the jet axis and its periphery. This voltage is created by a rotating black hole and transmitted along magnetic field lines into the jet. It is shown that the trajectories of proton in the jet are divided into three groups: untrapped, trapped and not accelerated. Untrapped particles are not kept by poloidal and toroidal magnetic fields inside the jet, so they escape out the jet and their energy is equal to the maximum value, $eU$. Trapped protons are moving along the jet with oscillations in the radial direction. Their energy varies around the value of $0.74 eU$. In a strong magnetic field protons preaccelerated in the magnetosphere are pressed to the jet axis and practically are not accelerated in the jet. The work defines acceleration regimes for a range of the most well-known AGN objects with relativistic jets and for the microquasar SS433.

astro-ph.HE↗

arXiv2020

Extinct radio pulsars as a source of subrelativistic positrons

Extinct radio pulsars, in which stationary, self-sustaining generation of a relativistic electron-positron plasma becomes impossible when rotation brakes down, can be sources of a subrelativistic flux of positrons and electrons. We assume that the observed excess of positrons in the bulge and the disc of the Galaxy is associated with these old neutron stars. The production of pairs in their magnetospheres occurs due to one-photon absorption of gamma quanta of the Galactic and extragalactic backgrounds. The cascade process of plasma production leads to the flux of positrons escaping from the open magnetosphere $\simeq 3 \times 10^{34} \text{ s}^{-1}$. The total flux of positrons from all old Galactic neutron stars with rotational periods $1.5 < P < 35$ s is $\simeq 3 \times 10^{43} \text{ s}^{-1}$. The energy of positrons is less than $\simeq 10$ MeV. The estimated characteristics satisfy the requirements for the positron source responsible for the 511-keV Galactic annihilation line.

astro-ph.HE↗

arXiv2020

Centrifugal acceleration of protons by a supermassive black hole

The centrifugal acceleration is due to the rotating poloidal magnetic field in the magnetosphere creates the electric field which is orthogonal to the magnetic field. Charged particles with finite cyclotron radii can move along the electric field and receive energy. Centrifugal acceleration pushes particles to the periphery, where their azimuthal velocity reaches the light speed. We have calculated particle trajectories by numerical and analytical methods. The maximum obtained energies depend on the parameter of the particle magnetization $ κ$, which is the ratio of rotation frequency of magnetic field lines in the magnetosphere $ Ω_F $ to non-relativistic cyclotron frequency of particles $ ω_c $, $ κ= Ω_F /ω_c << 1 $, and from the parameter $ α$ which is the ratio of toroidal magnetic field $ B_T $ to the poloidal one $ B_P $, $ α= B_T / B_P $. It is shown that for small toroidal fields, $ α<κ^{1/4} $, the maximum Lorentz factor $ γ_m $ is only the square root of magnetization, $ γ_m = κ^{-1/2} $, while for large toroidal fields, $ α>κ^{1/4} $, the energy increases significantly, $ γ_m = κ^{-2/3} $. However, the maximum possible acceleration, $ γ_m = κ^{-1} $, is not achieved in the magnetosphere. For a number of active galactic nuclei, such as M87, maximum values of Lorentz factor for accelerated protons are found. Also for special case of Sgr. A* estimations of the maximum proton energy and its energy flux are obtained. They are in agreement with experimental data obtained by HESS Cherenkov telescope.

astro-ph.HE↗

arXiv2019

On the thermal effects on radio waves propagating in the pulsar magnetosphere

Thermal effects on the properties of four electromagnetic waves propagating in the pulsar magnetosphere are analyzed. It is shown that thermal effects change only quantitatively the dispersion properties of superluminal ordinary O-mode freely escaping the pulsar magnetosphere; properties of the extraordinary X-mode remain unchanged. As for two subluminal waves propagating along magnetic field lines, for them thermal effects result in essential absorption. However, this attenuation occurs at considerable distances from the neutron star, so there is no doubt in their existence.

astro-ph.HE↗

arXiv2018

Diffusion of charged particles in a stochastic force-free magnetic field

We study diffusion of charged particles in stationary stochastic magnetic field ${\bf B}$ with zero mean, $\langle {\bf B} \rangle = 0 $. In the case when electric current is carried by electrons, the field is force-free, $\mathrm{curl} \,{\bf B} = α{\bf B} $, where $α({\bf r})$ is an arbitrary scalar function. In a small region where the function $α$ and the field magnitude $|{\bf B}|$ are approximately constant, the equations of motion of charged particles are integrated and reduced to the equation of mathematical pendulum. The transition from trapped to untrapped particles is continuously traced. Averaging over the magnetic field spectrum gives the spatial diffusion coefficient $D$ of particles as a function of the Larmor radius $r_L$ in the large-scale magnetic fields ($B_{LS}$) and magnetic field correlation length $L_0$. The diffusion coefficient turns out to be proportional to the Larmor radius, $D\propto r_L $, for $r_L L_0 /2π$. We apply obtained results to the diffusion of cosmic rays in the Galaxy, which contains a large number of independent regions with parameters $L_0$ and $B_{LS}$ varying in wide range. We average over $B_{LS}$ with the Kolmogorov spectrum and over $L_0$ with the distribution function $f(L_0)\propto L_0^{- 1+ σ}$. For the practically flat spectrum $σ= 1/15$, we have $ D\propto r_m^{0.7}$, which is consistent with observations.

astro-ph.HE↗

arXiv2015

Magnetic field evolution of accreting neutron stars

The flow of a matter, accreting onto a magnetized neutron star, is accompanied by an electric current. The closing of the electric current occurs in the crust of a neutron stars in the polar region across the magnetic field. But the conductivity of the crust along the magnetic field greatly exceeds the conductivity across the field, so the current penetrates deep into the crust down up to the super conducting core. The magnetic field, generated by the accretion current, increases greatly with the depth of penetration due to the Hall conductivity of the crust is also much larger than the transverse conductivity. As a result, the current begins to flow mainly in the toroidal direction, creating a strong longitudinal magnetic field, far exceeding an initial dipole field. This field exists only in the narrow polar tube of $r$ width, narrowing with the depth, i.e. with increasing of the crust density $ρ$, $r\propto ρ^{-1/4}$. Accordingly, the magnetic field $B$ in the tube increases with the depth, $B\propto ρ^{1/2}$, and reaches the value of about $10^{17}$ Gauss in the core. It destroys super conducting vortices in the core of a star in the narrow region of the size of the order of ten centimeters. Because of generated density gradient of vortices they constantly flow into this dead zone and the number of vortices decreases, the magnetic field of a star decreases as well. The attenuation of the magnetic field is exponential, $B=B_0(1+t/τ)^{-1}$. The characteristic time of decreasing of the magnetic field $τ$ is equal to $τ\simeq 10^3$ years. Thus, the magnetic field of accreted neutron stars decreases to values of $10^8 - 10^9$ Gauss during $10^7-10^6$ years.

astro-ph.HE↗

arXiv2014

Cosmic rays: extragalactic and Galactic

From the analysis of the flux of high energy particles, $E>3\cdot 10^{18}eV$, it is shown that the distribution of the power density of extragalactic rays over energy is of the power law, ${\bar q}(E)\propto E^{-2.7}$, with the same index of $2.7$ that has the distribution of Galactic cosmic rays before so called 'knee', $E<3\cdot 10^{15}eV$. However, the average power of extragalactic sources, which is of ${\cal E}\simeq 10^{43}erg \,s^{-1}$, at least two orders exceeds the power emitted by the Galaxy in cosmic rays, assuming that the density of galaxies is estimated as $N_g\simeq 1 Mpc^{-3}$. Considering that such power can be provided by relativistic jets from active galactic nuclei with the power ${\cal E}\simeq 10^{45} - 10^{46} erg \, s^{-1}$, we estimate the density of extragalactic sources of cosmic rays as $N_g\simeq 10^{-2}-10^{-3}\, Mpc^{-3}$. Assuming the same nature of Galactic and extragalactic rays, we conclude that the Galactic rays were produced by a relativistic jet emitted from the Galactic center during the period of its activity in the past. The remnants of a bipolar jet are now observed in the form of bubbles of relativistic gas above and below the Galactic plane. The break, observed in the spectrum of Galactic rays ('knee'), is explained by fast escape of energetic particle, $E>3\cdot 10^{15}eV$, from the Galaxy because of the dependence of the coefficient of diffusion of cosmic rays on energy, $D\propto E^{0.7}$. The obtained index of the density distribution of particles over energy, $N(E)\propto E^{-2.7-0.7/2}=E^{-3.05}$, for $E>3\cdot 10^{15}eV$ agrees well with the observed one, $N(E)\propto E^{-3.1}$. Estimated time of termination of the jet in the Galaxy is $4.2\cdot 10^{4}$ years ago.

astro-ph.HE↗

arXiv2013

Magnetic field generation in galactic molecular clouds

We investigate the magnetic field which is generated by turbulent motions of a weakly ionized gas. Galactic molecular clouds give us an example of such a medium. As in the Kazantsev-Kraichnan model we assume a medium to be homogeneous and a neutral gas velocity field to be isotropic and delta-correlated in time. We take into consideration the presence of a mean magnetic field, which defines a preferred direction in space and eliminates isotropy of magnetic field correlators. Evolution equations for the anisotropic correlation function are derived. Isotropic cases with zero mean magnetic field as well as with small mean magnetic field are investigated. It is shown that stationary bounded solutions exist only in the presence of the mean magnetic field for the Kolmogorov neutral gas turbulence. The dependence of the magnetic field fluctuations amplitude on the mean field is calculated. The stationary anisotropic solution for the magnetic turbulence is also obtained for large values of the mean magnetic field.

astro-ph.GA↗

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↗

arXiv2012

Disk accretion onto a magnetized star

The problem of interaction of the rotating magnetic field, frozen to a star, with a thin well conducting accretion disk is solved exactly. It is shown that a disk pushes the magnetic field lines towards a star, compressing the stellar dipole magnetic field. At the point of corotation, where the Keplerian rotation frequency coincides with the frequency of the stellar rotation, the loop of the electric current appears. The electric currents flow in the magnetosphere only along two particular magnetic surfaces, which connect the corotation region and the inner edge of a disk with the stellar surface. It is shown that the closed current surface encloses the magnetosphere. Rotation of a disk is stopped at some distance from the stellar surface, which is 0.55 of the corotation radius. Accretion from a disk spins up the stellar rotation. The angular momentum transferred to the star is determined.

astro-ph.GA↗

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

Formation of "Lightnings" in a Neutron Star Magnetosphere and the Nature of RRATs

The connection between the radio emission from "lightnings" produced by the absorption of high-energy photons from the cosmic gamma-ray background in a neutron star magnetosphere and radio bursts from rotating radio transients (RRATs) is investigated. The lightning length reaches 1000 km; the lightning radius is 100 m and is comparable to the polar cap radius. If a closed magnetosphere is filled with a dense plasma, then lightnings are efficiently formed only in the region of open magnetic field lines. For the radio emission from a separate lightning to be observed, the polar cap of the neutron star must be directed toward the observer and, at the same time, the lightning must be formed. The maximum burst rate is related to the time of the plasma outflow from the polar cap region. The typical interval between two consecutive bursts is ~100 s. The width of a single radio burst can be determined both by the width of the emission cone formed by the lightning emitting regions at some height above the neutron star surface and by a finite lightning lifetime. The width of the phase distribution for radio bursts from RRATs, along with the integrated pulse width, is determined by the width of the bundle of open magnetic field lines at the formation height of the radio emission. The results obtained are consistent with the currently available data and are indicative of a close connection between RRATs, intermittent pulsars, and extreme nullers.

astro-ph.HE↗

arXiv2011

Absorption of Gamma-Ray Photons in a Vacuum Neutron Star Magnetosphere: I. Electron-Positron Pair Production

The production of electron-positron pairs in a vacuum neutron star magnetosphere is investigated for both low (compared to the Schwinger one) and high magnetic fields. The case of a strong longitudinal electric field where the produced electrons and positrons acquire a stationary Lorentz factor in a short time is considered. The source of electron-positron pairs has been calculated with allowance made for the pair production by curvature and synchrotron photons. Synchrotron photons are shown to make a major contribution to the total pair production rate in a weak magnetic field. At the same time, the contribution from bremsstrahlung photons may be neglected. The existence of a time delay due to the finiteness of the electron and positron acceleration time leads to a great reduction in the electron-positron plasma generation rate compared to the case of a zero time delay. The effective local source of electron-positron pairs has been constructed. It can be used in the hydrodynamic equations that describe the development of a cascade after the absorption of a photon from the cosmic gamma-ray background in a neutron star magnetosphere.

astro-ph.HE↗

arXiv2011

Absorption of Gamma-Ray Photons in a Vacuum Neutron Star Magnetosphere: II. The Formation of "Lightnings"

The absorption of a high-energy photon from the external cosmic gamma-ray background in the inner neutron star magnetosphere triggers the generation of a secondary electron-positron plasma and gives rise to a lightning - a lengthening and simultaneously expanding plasma tube. It propagates along magnetic fields lines with a velocity close to the speed of light. The high electron-positron plasma generation rate leads to dynamical screening of the longitudinal electric field that is provided not by charge separation but by electric current growth in the lightning. The lightning radius is comparable to the polar cap radius of a radio pulsar. The number of electron-positron pairs produced in the lightning in its lifetime reaches 10^28. The density of the forming plasma is comparable to or even higher than that in the polar cap regions of ordinary pulsars. This suggests that the radio emission from individual lightnings can be observed. Since the formation time of the radio emission is limited by the lightning lifetime, the possible single short radio bursts may be associated with rotating radio transients (RRATs).

astro-ph.HE↗

arXiv2011

On the origin of galactic cosmic rays

It is shown that the relativistic jet, emitted from the center of the Galaxy during its activity, possessed power and energy spectrum of accelerated protons sufficient to explain the current cosmic rays distribution in the Galaxy. Proton acceleration takes place on the light cylinder surface formed by the rotation of a massive black hole carring into rotation the radial magnetic field and the magnetosphere. Observed in gamma, x-ray and radio bands bubbles above and below the galactic plane can be remnants of this bipolar get. The size of the bubble defines the time of the jet's start, $\simeq 2.4\cdot 10^7$ years ago. The jet worked more than $10^7$ years, but less than $2.4\cdot10^7$ years.

astro-ph.GA↗

arXiv2010

Electron-Positron Plasma Generation in a Magnetar Magnetosphere

We consider the electron-positron plasma generation processes in the magnetospheres of magnetars - neutron stars with strong surface magnetic fields, B = 10^(14) - 10^(15) G. We show that the photon splitting in a magnetic field, which is effective at large field strengths, does not lead to the suppression of plasma multiplication, but manifests itself in a high polarization of gamma-ray photons. A high magnetic field strength does not give rise to the second generation of particles produced by synchrotron photons. However, the density of the first-generation particles produced by curvature photons in the magnetospheres of magnetars can exceed the density of the same particles in the magnetospheres of ordinary radio pulsars. The plasma generation inefficiency can be attributed only to slow magnetar rotation, which causes the energy range of the produced particles to narrow. We have found a boundary in the P - Pdot diagram that defines the plasma generation threshold in a magnetar magnetosphere.

astro-ph↗