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S. V. Bogovalov

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

At least 19 recordsLinked to original sources
arXiv2024

Waves in strong centrifugal filed: dissipative gas

In the fast rotating gas (with the velocity typical for Iguassu gas centrifuge) three families of linear waves exist with different polarizations and law of dispersion. The energy of the waves is basically concentrated at the axis of rotation in the rarefied region. Therefore these waves decay on the distance comparable with the wavelength. There is only one type of waves propagating strictly along the axis of rotation with the law of dispersion similar to ordinary acoustic waves. These waves are interested for the physics of gas centrifuges. The energy density of these waves concentrates at the wall of the rotor. These waves have weak damping due to the molecular viscosity and heat conductivity. The damping coefficient is determined for this type of waves by numerical calculations. Analytical approximations for the damping coefficient is defined as well. At the parameters typical for the Iguassu centrifuge the damping is defined by interaction of the waves with the rotor wall.

physics.flu-dyn↗
arXiv2019

Magnetic absorption of VHE photons in the magnetosphere of the Crab pulsar

The detection of the pulsed $\sim 1 $~TeV gamma-ray emission from the Crab pulsar reported by MAGIC and VERITAS collaborations demands a substantial revision of existing models of particle acceleration in the pulsar magnetosphere. In this regard model independent restrictions on the possible production site of the VHE photons become an important issue. In this paper, we consider limitations imposed by the process of conversion of VHE gamma rays into $e^{\pm}$ pairs in the magnetic field of the pulsar magnetosphere. Photons with energies exceeding 1~TeV are effectively absorbed even at large distances from the surface of the neutron star. Our calculations of magnetic absorption in the force-free magnetosphere show that the twisting of the magnetic field due to the pulsar rotation makes the magnetosphere more transparent compared to the dipole magnetosphere. The gamma-ray absorption appears stronger for photons emitted in the direction of rotation than in the opposite direction. There is a small angular cone inside which the magnetosphere is relatively transparent and photons with energy $1.5$~TeV can escape from distances beyond $0.1$~light cylinder radius ($R_{\rm{lc}}$). The emission surface from where photons can be emitted in the observer's direction further restricts the sites of VHE gamma-ray production. For the observation angle $57^{\circ}$ relative to the Crab pulsar axis of rotation and the orthogonal rotation, the emission surface in the open field line region is located as close as $0.4\,R_{\rm{lc}}$ from the stellar surface for a dipole magnetic field, and $0.1\,R_{\rm{lc}}$ for a force-free magnetic field.

astro-ph.HE↗
arXiv2018

Ratio of kinetic luminosity of the jet to bolometric luminosity of the disk at the "cold" accretion onto a supermassive black hole

Disk accretion onto black holes is accompanied by collimated outflows (jets). In active galactic nuclei (AGN), the kinetic energy flux of the jet may exceed the bolometric luminosity of the disk a few orders of magnitude. This phenomena can be explained in frameworks of so called "cold" disk accretion when the only source of energy of AGN is the energy released at the accretion. The radiation from the disk is suppressed because the wind from the disk carries out almost all the angular momentum and the gravitational energy of the accreted material. In this paper, we calculate an unavoidable radiation from the "cold" disk and the ratio of the kinetic energy luminosity of the outflow to the bolometric luminosity of the accretion disk around a super massive black hole in framework of the paradigm of the optically thick alpha-disk of Shakura \& Sunyaev. The ratio of the luminosities is defined predominantly by the ratio of the magnetic field pressure inside the disk to the magnetic field pressure at the base of the wind. The obtained equations applied to the jet of M87 demonstrate good agreement with observations. In the case of Sgr A*, these equations allow us to predict the kinetic energy flux from the disk around Galactic SMBH.

astro-ph.HE↗
arXiv2017

3D numerical modeling of liquid metal turbulent flow in an annular linear induction pump

3D numerical simulation of the liquid metal flow affected by electromagnetic field in the Annular Linear Induction Pump (ALIP) is performed using modified ANSYS package. ANSYS/EMAG has been modified to take into account arbitrary velocity field at the calculation of the electromagnetic field and has been unified with CFX to provide integration of all the system of magnetohydrodynamic (MHD) equations defining dynamics of the conductive media in the variable electromagnetic field. The non-stationary problem is solved taking into account the influence of the metal flow on the electromagnetic field. The pump performance curve and the dependence of the pump efficiency on a flow rate are obtained.

physics.app-ph↗
arXiv2017

Dependence of the separative power of an optimised Iguassu gas centrifuge on the velocity of rotor

Purpose - The purpose of this work is to determine dependence of the separative power of the Iguassu gas centrifuge (GC) on the velocity of the rotor. Design/methodology/approach - The dependence is determined by means of computer simulation of the gas flow in the GC and numerical solution of the diffusion equation for the light component of the binary mixture of uranium isotopes. 2D axisymmetric model with the sources/sinks of the mass, angular momentum and energy reproducing the scoops was explored for the computer simulation. Parameters of the model correspond to the parameters of the so-called Iguassu centrifuge. The separative power has been optimised in relation to the pressure of the gas, temperature of the gas, the temperature drop along the rotor, power of the source of angularmomentum and energy, feed flow and geometry of the lower baffle. Findings - In the result, the optimised separative power depends only on the velocity, length and diameter of the rotor. The dependence on the velocity is described by the power law function with the power law index 2.6 which demonstrate stronger dependence on the velocity than it follows from experimental data. However, the separative power obtained with limitation on the pressure growth with the velocity depends on the velocity on the power similar to 2 which well agree with the experiments. Originality/value - For the first time, the optimised separative power of the GCs have been calculated via numerical simulation of the gas flow and diffusion of the binary mixture of isotope.

physics.flu-dyn↗
arXiv2017

Waves in strong centrifugal fields: dissipationless gas

Linear waves are investigated in a rotating gas under the condition of strong centrifugal acceleration of the order $10^6 g$ realized in gas centrifuges for separation of uranium isotopes. Sound waves splits into three families of the waves under these conditions. Dispersion equations are obtained. The characteristics of the waves strongly differ from the conventional sound waves on polarisation, velocity of propagation and distribution of energy of the waves in space for two families having frequencies above and below the frequency of the conventional sound waves. The energy of these waves is localized in rarefied region of the gas. The waves of the third family were not specified before. They propagate exactly along the rotational axis with the conventional sound velocity. These waves are polarized only along the rotational axis. Radial and azimuthal motions are not excited. Energy of the waves is concentrated near the wall of the rotor where the density of the gas is largest.

physics.flu-dyn↗
arXiv2017

Gas dynamics in strong centrifugal fields

Dynamics of waves generated by scopes in gas centrifuges (GC) for isotope separation is considered. The centrifugal acceleration in the GC reaches values of the order of $10^6$g. The centrifugal and Coriolis forces modify essentially the conventional sound waves. Three families of the waves with different polarisation and dispersion exist in these conditions. Dynamics of the flow in the model GC Iguasu is investigated numerically. Comparison of the results of the numerical modelling of the wave dynamics with the analytical predictions is performed. New phenomena of the resonances in the GC is found. The resonances occur for the waves polarized along the rotational axis having the smallest dumping due to the viscosity.

physics.flu-dyn↗
arXiv2015

Separative power of an optimised concurrent gas centrifuge

The problem of separation of uranium isotopes in a concurrent gas centrifuge is solved analytically. Separative power of the optimized concurrent gas centrifuges equals to $δU=12.7(V/700~{\rm m/s})^2 (300 ~{\rm K}/T)L, ~{\rm kg ~SWU/yr}$, where $L$ and $V$ are the length and linear velocity of the rotor of the gas centrifuge, $T$ is the temperature. This formula well agrees with an empirical separative power of counter current gas centrifuges. The optimal value of the separative power is not unique on the plane $(p_w,v_z)$, where $p_w$ is pressure at the wall of the rotor and $v_z$ is axial velocity of the gas. This value is constant on a line defined by the equation $p_wv_z=constant$. Equations defining the mass flux and the electric power necessary to support the rotation of the gas centrifuge are obtained.

physics.flu-dyn↗
arXiv2014

Magnetocentrifugal acceleration of bulk motion of plasma in pulsar magnetosphere

Acceleration of bulk motion of plasma due to magneto centrifugal mechanism is investigated for different shapes of the field lines of 3-D magnetic field. It is shown that this mechanism can be efficient provided that the field line is twisted into direction of rotation. According to the last results of the numerical modelling a fraction of the field lines with such geometrical shape apparently exist in the pulsar magnetosphere close to the last closed field line. In this case the Lorentz factor $γ$ increases with the radius $r$ along these field lines as $γ\sim (1-(rΩ/c)^2)^{-1}$, where $Ω$ - angular velocity of the pulsar rotation. The magneto centrifugal mechanism provides acceleration of the electrons to the energy which is sufficient to explain the observed VHE pulsed $γ$-rays from Crab pulsar.

astro-ph.HE↗
arXiv2012

Post-Periastron Gamma Ray Flare from PSR B1259-63/LS 2883 as a Result of Comptonization of the Cold Pulsar Wind

We argue that the bright flare of the binary pulsar \object{PSR B1259$-$63/LS2883} detected by the {\it Fermi} Large Area Telescope (LAT), is due to the inverse Compton (IC) scattering of the unshocked electron-positron pulsar wind with a Lorentz factor $Γ_0 \approx 10^4$. The combination of two effects both linked to the circumstellar disk (CD), is a key element in the proposed model. The first effect is related to the impact of the surrounding medium on the termination of the pulsar wind. Inside the disk, the "early" termination of the wind results in suppression of its gamma-ray luminosity. When the pulsar escapes the disk, the conditions for termination of the wind undergo significant changes. This would lead to a dramatic increase of the pulsar wind zone, and thus to the proportional increase of the gamma-ray flux. On the other hand, if the parts of the CD disturbed by the pulsar can supply infrared photons of density high enough for efficient Comptonization of the wind, almost the entire kinetic energy of the pulsar wind would be converted to radiation, thus the gamma-ray luminosity of the wind could approach to the level of the pulsar's spin-down luminosity as reported by the {\it Fermi} collaboration.

astro-ph.HE↗
arXiv2009

Synthetic synchrotron emission maps from MHD models for the jet of M87

We present self-consistent global, steady-state MHD models and synthetic optically thin synchrotron emission maps for the jet of M87. The model consist of two distinct zones: an inner relativistic outflow, which we identify with the observed jet, and an outer cold disk-wind. While the former does not self-collimate efficiently due to its high effective inertia, the latter fulfills all the conditions for efficient collimation by the magneto-centrifugal mechanism. Given the right balance between the effective inertia of the inner flow and the collimation efficiency of the outer disk wind, the relativistic flow is magnetically confined into a well collimated beam and matches the measurements of the opening angle of M87 over several orders of magnitude in spatial extent. The synthetic synchrotron maps reproduce the morphological structure of the jet of M87, i.e. center-bright profiles near the core and limb-bright profiles away from the core. At the same time, they also show a local increase of brightness at some distance along the axis associated to a recollimation shock in the MHD model. Its location coincides with the position of the optical knot HST-1. In addition our best fitting model is consistent with a number of observational constraints such as the magnetic field in the knot HST-1, and the jet-to-counterjet brightness ratio.

astro-ph.GA↗
arXiv2008

Hydrodynamics of interaction of pulsar and stellar winds and its impact on the high energy radiation of binary pulsar systems

The hydrodynamics of the interaction of pulsar and stellar winds in binary systems harboring a pulsar and its impact on the nonthermal radiation of the binary pulsar PSR B1259-63/SS2883 is discussed. The collision of an ultrarelativistic pulsar wind with a nonrelativistic stellar outflow results in significant bulk acceleration of the shocked material from the pulsar wind. Already at distances comparable to the size of the binary system, the Lorentz factor of the shocked flow can be as large as $γ$~4. This results in significant anisotropy of the inverse Compton radiation of accelerated electrons. Because of the Doppler boosting of the produced radiation, one should expect a variable gamma-ray signal from the system. In particular, this effect may naturally explain the reported tendency of a decrease of TeV gamma-ray flux close to the periastron. The modeling of the interaction of pulsar and stellar winds allows self-consistent calculations of adiabatic losses. Our results show that adiabatic losses dominate over the radiative losses. These results have direct impact on the orbital variability of radio, X-ray and gamma-ray signals detected from the binary pulsar PSR 1259-63/SS2883.

astro-ph↗
arXiv2007

Modeling interaction of relativistic and nonrelativistic winds in binary system PSR 1259-63/SS2883. I.Hydrodynamical limit

In this paper, we present a detailed hydrodynamical study of the properties of the flow produced by the collision of a pulsar wind with the surrounding in a binary system. This work is the first attempt to simulate interaction of the ultrarelativistic flow (pulsar wind) with the nonrelativistic stellar wind. Obtained results show that the wind collision could result in the formation of an "unclosed" (at spatial scales comparable to the binary system size) pulsar wind termination shock even when the stellar wind ram pressure exceeds significantly the pulsar wind kinetical pressure. Moreover, the post-shock flow propagates in a rather narrow region, with very high bulk Lorentz factor ($γ\sim100$). This flow acceleration is related to adiabatical losses, which are purely hydrodynamical effects. Interestingly, in this particular case, no magnetic field is required for formation of the ultrarelativistic bulk outflow. The obtained results provide a new interpretation for the orbital variability of radio, X-ray and gamma-ray signals detected from binary pulsar system PSR 1259-63/SS2883.

astro-ph↗
arXiv2005

Magnetic collimation of the relativistic jet in M87

We apply a two-zone MHD model to the jet of M87. The model consists of an inner relativistic outflow, which is surrounded by a non-relativistic outer disk-wind. The outer disk-wind collimates very well through magnetic self-collimation and confines the inner relativistic jet into a narrow region around the rotation axis. Further, we show by example, that such models reproduce very accurately the observed opening angle of the M87 jet over a large range from the kiloparsec scale down to the sub-parsec scale.

astro-ph↗
arXiv2002

On the origin of the torus and jet-like structures in the centre of Crab Nebula

The formation of the toroidal and jet-like structures in the central part of the Crab Nebula is explained in the framework of Kennel & Coroniti theory. The only new element introduced by us in this theory is the initial anisotropy of the energy flux in the wind. We estimate the X-ray surface brightness of the Crab Nebula from the region of interaction of this wind with the interstellar medium and compare it with observations.

astro-ph↗
arXiv2002

The Crab Nebula: interpretation of CHANDRA observations

We interpret the observed X-ray morphology of the central part of the Crab Nebula (torus + jets) in terms of the standard theory by Kennel and Coroniti (1984). The only new element is the inclusion of anisotropy in the energy flux from the pulsar in the theory. In the standard theory of relativistic winds, the Lorentz factor of the particles in front of the shock that terminates the pulsar relativistic wind depends on the polar angle as $γ=γ_0+γ_m\sin^2θ$, where $γ_0 \sim 200$ and $γ_m \sim 4.5\times 10^6$. The plasma flow in the wind is isotropic. After the passage of the pulsar wind through the shock, the flow becomes subsonic with a roughly constant (over the plerion volume) pressure $P={1\over 3}nε$, where $n$ is the plasma particle density and $ε$ is the mean particle energy. Since $ε\sim γmc^2$, a low-density region filled with the most energetic electrons is formed near the equator. A bright torus of synchrotron radiation develops here. Jet-like regions are formed along the pulsar rotation axis, where the particle density is almost four orders of magnitude higher than that in the equatorial plane, because the particle energy there is four orders of magnitude lower. The energy of these particles is too low to produce detectable synchrotron radiation. However, these quasi-jets become comparable in brightness to the torus if additional particle acceleration takes place in the plerion. We also present the results of our study of the hydrodynamic interaction between an anisotropic wind and the interstellar medium. We compare the calculated and observed distributions of the volume intensity of X-ray radiation.

astro-ph↗
arXiv2000

Magnetocentrifugal acceleration of plasma in a nonaxisymmetric magnetosphere

Violation of the axial synnetry of a magnetic field essentially modifies the physics of the plasma outflow in the magnetosphere of rotating objects. In comparison to the axisymmetric outflow, two new affects appear: more efficient magnetocentrifugal acceleration of the plasma along particular field lines and generation of MHD waves. Here, we use an ideal MHD approximation to study the dynamics of a cold wind in the nonaxisymmetric magnetosphere. We obtain a self-consistent analytical solution of the problem of cold plasma outflow from a slowly rotating star with a slightly nonaxisymmetric magnetic field using perturbation theory. In the axisymmetric (monopole-like) magnetic field, the first term in the expansion of the terminating energy of the plasama in powers of $Ω$ is proportional to $Ω^4$, where $Ω$ is the angular velocity of the central source. Violation of the axial symmetry of the magnetic field crucially changes this dependence. The first correction to the energy of the plasma becomes proportional to $Ω$. Efficient magnetocentrifugal acceleration occurs along the field lines curved initially in the direction of the rotation. I argue that all necessary conditions for the efficient magnetocentrifugal acceleration of the plasma exist in the radio pulsar megnetosphere. We calculated the first correction of the rotational losses due to the generation of the MHD waves and analysed the plasma acceleration by these waves.

astro-ph↗