Relativistic Electron-positron Research Articles

Nonlinear Dynamics in the Relativistic Plasma of Astrophysical High‐Energy Sources

Relativistic plasmas are interesting media for particle acceleration, especially when their kinetic pressure is in rough equipartition with the magnetic pressure. Indeed, when in rough equipartition, these relativistic plasmas have generalized Alfven waves that propagate at velocities close to the velocity of light, which makes the acceleration process more efficient than usual. With this in mind, we have investigated some properties that are of interest to several issues in high-energy astrophysics, such as the source of high-energy cosmic rays, the origin of the high-energy emission of blazars and microquasars, the synchrotron radiation of jets, and the gamma-ray bursts of cosmic fireballs. Three types of relativistic plasmas are considered: plasma dominated by the relativistic proton component (high-energy cosmic rays), plasma dominated by highly relativistic electrons (the protons being nonrelativistic), and plasma dominated by relativistic electron-positron pairs. Electron or pair-dominated plasmas are interesting on the one hand because of their fast dynamics, and on other hand because the energy of magnetic perturbations goes directly into the radiative particles. The energy transfer from the electromagnetic perturbations to the particles depends on the nonlinear dynamics. We derive the nonlinear systems that govern the dynamics of these relativistic plasmas close to equipartition. We discuss the possibility of self-modulation instability and soliton formation and demonstrate the existence of a transition at equipartition that has remarkable mathematical properties. We show that particle acceleration in a pair plasma is efficient only when the plasma pressure is below the equipartition value. We give intuitive arguments that this would also be true for the other plasmas, but we do not yet have firm proof. Thus, a pair plasma has a regulation mechanism toward equipartition, since radiation cooling is not efficiently balanced above equipartition. This is an interesting issue for nonthermal radio sources. We have also devised a new kind of collisionless quasi-parallel relativistic shock when a relativistic pair cloud pervades an ambient medium. The proton backstream in the relativistic front drives a monochromatic wave responsible for strong nonlinearities that heat the relativistic plasma. The instability is quenched when the relativistic plasma has been sufficiently heated.

Nonlinear Compton scattering and electron acceleration in interfering laser beams

The exact solution of the classical nonlinear equation of motion for a relativistic electron in the field of two electromagnetic (EM) waves is obtained. For the particular case of the linearly polarized standing EM wave in the planar optical cavity, intensity of the nonlinear Compton scattering, the time of flight, and the momentum variation after the relativistic electron passes along the cavity axis are calculated in weak and strong field limits. These effects depend on the initial phase of the EM wave at the electron entrance into the cavity and can be used for producing, diagnostics, and acceleration of relativistic electron (positron) microbunches.

The terminal bulk Lorentz factor of relativistic electron-positron jets

We present numerical simulation of bulk Lorentz factor of relativistic electron-positron jet driven by Compton rocket effect from accretion disc radiation. The plasma is assumed to have a power-law distribution $n_{e}(\gamma) \propto \gamma^{-s}$ whith $1 < \gamma< \gamma_{max}$ and is continuously reheated to compensate for radiation losses. We include full Klein-Nishina (hereafter KN) cross section, and study the role of energy upper cut-off $\gamma_{max}$, spectral index $s$, and source compactness. We determine terminal bulk Lorentz factor in the case of supermassive black holes relevant to AGN and stellar black holes relevant to galactic microquasars. In the latter case, Klein-Nishina cross section effect are more important, and induce terminal bulk Lorentz factor smaller than in the former case. Our result are in good agreement with bulk Lorentz factors observed in galactic sources (GRS1915+105, GROJ1655-40) and extragalactic ones. Differences in scattered radiation and acceleration mechanism efficiency in AGN environment can be responsible for the variety of relativistic motion in those objects. We also take into account the influence of the size of the accretion disc; if the external radius is small enough, the bulk Lorentz factor can be as high as 60.

Bi-Hamiltonian structure and (non)integrability of nonlinear wave equations

Parallel propagation of magnetohydrodynamic waves in relativistic electron–positron plasmas is described by a vector version of the modified Korteweg–de Vries equation. This is shown to be nonintegrable by the bi-Hamiltonian structure method, because it fails to provide the recursion operator needed to generate an infinite sequence of conserved densities. Only three of these conserved densities had been found explicitly by direct investigations based on the symmetry properties of the new equation.

Nonlinear Drift-Alfvén Waves in Relativistically Hot Nonuniform Electron-Positron Plasmas

The magnetic viscosity tensor is derived for a magnetized relativistic collisionless plasma with temperature gradients. By means of this tensor we deduce the nonlinear equations for drift–Alfven waves in a relativistic electron-positron low β plasma with density and temperature gradients. It is shown that our new equations have solutions in the form of dipolar vortices. The present results should be relevant to a number of astrophysical objects with strong electron-positron pair production, e.g. in pulsars as well as in accretion disks and jets.

Generation of Crab Nebulae Wisps by Plasma Drift Instability

A new mechanism of wisp formation in the Crab Nebula, without recourse to a shock wave, is presented. The mechanism is based on the plasma processes taking place in the relativistic electron-positron plasma, in particular, on excitation of the drift instability in the slightly inhomogeneous magnetic field of the nebula. The magnetic field geometry is assumed to be untwisting spiral-like, concentrated around the rotational equatorial plane of the pulsar. We infer that the energy is transported from the pulsar to the nebula not only by the Poynting flux but also by the kinetic energy of the particles moving along the field lines. We consider a specific relativistic electron-positron plasma with Lorentz factor γ± ~ 10 penetrated by an ion beam with γb ~ 106. It is shown that in such a plasma, taking into account the drift, the generation of low-frequency waves propagating transversely to the magnetic field is possible. In this way the excited Br field causes additional alteration of the magnetic field geometry. The higher luminosity of certain spots is explained by the reorientation of the direction of motion of the synchrotron radiation source (Larmor circle) relative to the observer. The sizes, variability of luminosity, spatial asymmetry, polarization, and transfer velocity, i.e., the main properties of the wisps, are explained. Some predictions are also made.

Generation of the electrostatic field in the pulsar magnetosphere plasma

The behavior of a relativistic electron–positron plasma in the pulsar magnetosphere is investigated. The equation of the motion of the magnetospheric plasma is discussed, from which it follows that, if the plasma particle radial velocity Vr&amp;gt;c/√ (where c is the speed of light), the centrifugal acceleration changes its sign and the particle braking begins. The stability of the magnetospheric plasma with respect to the radially oriented potential perturbations is discussed and the possibility of the electrostatic field generation in this plasma along the pulsar magnetic field lines is shown.

Growth Rates of Envelope Modulations of Electromagnetic Waves in Relativistic Temperature Electron-Positron Plasmas, Stimulated by Weak Or Finite Phonon Damping

We study the modulational instability of an electron-positron plasma with relativistic temperatures and phonon damping. It is shown that when the phonon damping is O(1) or O(e), a modulational instability appears even for classical temperatures. When the phonon damping is O(e2)), we find that in the non-relativistic limit, previous results are recovered, and for ultrarelativistic temperatures, the instability occurs in a wider band around the relativistic plasma frequency.

Study of nonlinear alfven waves in an electron-positron plasma with a 3-D EM particle code

Results from 3-dimensional electromagnetic particle simulations of a magnetized electron-positron plasma with a relativistic electron beam ( γ = 2) are presented. As part of the initial conditions, a poloidal magnetic field is specified consistent with the current carried by the beam electrons. The beam undergoes pinching oscillations due to the pressure imbalance between the inside and outside of the beam. A transverse two-stream instability is excited with large helical perturbations. In the process, background electrons and positrons are accelerated up to relativistic energy levels. Only background electrons are accelerated further along the z-direction due to the synergetic effects by both the excited transverse mode and the accompanying electrostatic waves caused by the breakdown of the helical perturbations. Preliminary simulation results for a relativistic electron-positron jet show that shock waves excited at the jet head propagate into the jet and accelerate particles perpendicularly. The jet electrons are twisted at the front part of the jet.

Optical Pulse Polarization of the Crab Pulsar

The strong optical emission of the Crab pulsar allows us to study the polarization properties in detail. Optical pulsed emission can best be understood as synchrotron radiation of relativistic electron-positron pairs in the outer magnetosphere. We calculate the polarization properties of the optical pulses based on the outer gap model, which has explained much of the observed properties of this pulsar. We find that the calculated polarization profiles exhibit the same qualitative behaviors as the observations for a large range in parameter space. It seems that the optical polarizations do not constrain strongly on the Crab pulsar{close_quote}s emission geometry. {copyright} {ital 1996 The American Astronomical Society.}

Covariant relativistic hydrodynamics of multispecies plasma and generalized Ohm's law.

Fully covariant hydrodynamical equations for multi-species relativistic plasma in the external electromagnetic field are derived. The derived multi-fluid description takes into account binary Coulomb collisions, annihilation, and interaction with the photon background in terms of the invariant collision cross-sections. Generalized Ohm’s law is derived in a manifestly covariant form. Particular attention is devoted to the relativistic electron-positron plasma.

Instabilities in the magnetosphere of millisecond pulsars

A model explaining some observational properties of millisecond pulsars is presented in the framework of the general plasma model for pulsar emission developed by Al. Kazbegi, G. Machabeli, and G. Melikidze in a series of papers. In the region of the open magnetic field lines of the pulsar magnetosphere the existence of a relativistic electron-positron plasma penetrated by a primary particle beam is assumed. Wave excitation due to different plasma instabilities is considered. The main properties of pulsar radiation (e.g., existence of “core” and “cone” types of emission, circular polarization, subpulse drift phenomena, pulse nullings, and mode changing) are explained in the most natural way by this model. The observations show that despite the big difference between the physical parameters of the “typical” and millisecond pulsars their observed properties (pulse profiles, polarization, existence of two different modes in emission, frequency evolution, etc.) are more or less similiar and the physical mechanisms of their radiation do not differ fundamentally from each other. Some particular millisecond pulsars are considered based on the model presented, and predictions are made.

Path integral for problem of radiation of fast charged particles in matter

It is shown that the concept of Brownian motion and the path integral method based on it can be used to describe the emission of radiation by high-energy particles in matter. Within the scope of classical electrodynamics we have derived a new equation that describes the effect of multiple scattering on the differential spectrum and polarization characteristics of emission from a relativistic electron (positron) moving through a target of finite thickness. The results are of sufficient generality that we can obtain as limiting cases both the known equations for an amorphous medium and new equations for a crystal. We performed also a numerical analysis and compared angular distributions of radiation in oriented and non-oriented crystals of tungsten as an example.

Gamma-ray emission of blazars by a relativistic electron–positron beam

Gamma-ray emission of blazars by a relativistic electron–positron beam

A Signature of Relativistic Electron-Positron Beams in BL Lacertae Objects

view Abstract Citations (13) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Signature of Relativistic Electron-Positron Beams in BL Lacertae Objects Xie, G. Z. ; Liu, B. F. ; Wang, J. C. Abstract BL Lacertae objects have been observed to vary in all wavebands on various timescales ranging from years to hours. Compton Gamma Ray Observatory (CGRO) observations have revealed intense γ-ray emission from several BL Lac Objects. We show here that there is a significant correlation between the Doppler-corrected minimal X-ray luminosity and the equivalent timescale of X-ray variability extrapolated from the observed optical variability for BL Lac objects. We interpret this as evidence for relativistic electron-positron beams in BL Lac objects. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176463 Bibcode: 1995ApJ...454...50X Keywords: ELEMENTARY PARTICLES; GALAXIES: BL LACERTAE OBJECTS: GENERAL; GALAXIES: JETS; RADIATION MECHANISMS: NONTHERMAL full text sources ADS | data products SIMBAD (46) NED (45) HEASARC (1)

Fluctuations in the relativistic plasma and primordial magnetic fields.

The stochastic fluctuations of the electromagnetic field in a relativistic electron-positron plasma are studied. The correlation functions of the fluctuating four-current, electric and magnetic fields are computed to leading order using the Schwinger-Keldysh closed time path formulation of thermal field theory. As an application, we consider the scenario proposed by Tajima et al. for generating a primordial magnetic field from thermal fluctuations in the prerecombination plasma. We compute the level of magnetic fluctuations sustained by the pair plasma at or before the epoch of big bang nucleosynthesis and conclude that the early Universe was pervaded by a strong low-frequency, albeit small-scale, random magnetic field. The astrophysical implications are briefly discussed.

On the nature of non-thermal radiation from cosmological -ray bursters

Relativistic electron-positron winds with strong magnetic fields are considered as a source of radiation for cosmological $\gamma$-ray bursters. Such a wind is generated by a millisecond pulsar with a very strong magnetic field. An electron-positron plasma near the pulsar is optically thick and in quasi-thermodynamic equilibrium. It is shown that the main part of radiation from the pulsar wind is nonthermal and generates in the following way. Kinetic energy which is released in the process of deceleration of the neutron star rotation transforms mainly to the magnetic field energy. The magnetic field is frozen in the outflowing plasma if the distance to the pulsar is smaller than $\sim 10^{13}$ cm. This field transfers the energy from the pulsar environment to the region outside the $\gamma$-ray photosphere of the electron-positron wind. At a distance of more than $\sim 10^{13}$ cm the magnetohydrodynamic approximation for the pulsar wind is broken, and intense electromagnetic waves are generated. The frequency of these waves is equal to the frequency of the pulsar rotation. Outflowing particles are accelerated in the field of intense electromagnetic waves to Lorentz factors of the order of $10^6$ and generate nonthermal synchro-Compton radiation. The typical energy of nonthermal photons is $\sim 1$ MeV. A high-energy tail of the $\gamma$-ray spectrum may be up to $\sim 10^4$ MeV. Baryonic matter is ejected occasionally from the pulsar magnetosphere. The baryonic matter ejection and subsequent suppression of the $\gamma$-ray emission may be responsible for the time structure of $\gamma$-ray bursts.

Gamma-ray emission of active galactic nuclei as a signature of relativistic electron-positron beams

Gamma-ray emission from extragalactic sources is interpreted as the Doppler-boosted annihilation and inverse Compton radiation from a relativistic electron-positron beam. We argue that Doppler boosting is required to avoid a strong depletion by γ-γ pair production, but even so, the compactness cannot be smaller than unity at light-week scale with a reasonable Doppler factor. This strongly suggests the existence of a beamed electron-positron source. The case of the quasar 3C 279 is investigated in detail. We show that one can easily account for the observed luminosity and variability time scale with reasonable values of the plasma density and bulk Lorentz factor of the beam, in accordance with previous estimates based upon observations at other wavelengths (radio and X-rays)

Coherent Radio-Emission Mechanisms for Pulsars

AbstractCoherent emission mechanisms may be classified as (i) maser mechanisms, attributed to negative absorption by resonant particles in a resistive instability, (ii) a reactive or hydrodynamic instability, or (iii) to emission by bunches. Known coherent emission mechanisms in radio astronomy are plasma emission in solar radio bursts, maser emission in OH and other molecular line sources, electron-cyclotron maser emission from the planets, and pulsar emission. Pulsar radio emission is the brightest of all known coherent emission, and its brightness temperature is close to the maximum conceivable in terms of energy efficiency. Three possible pulsar radio emission mechanisms warrant serious consideration in polar cap models; here these are called coherent curvature emission, relativistic plasma emission, and free electron maser emission, respectively.1.Coherent curvature emission is attributed to emission by bunches. There is a fundamental weakness in existing theoretical treatments which do not allow for any velocity dispersion of the particles. There is no satisfactory mechanism for the formation of the required bunches, and were such bunches to form they would quickly lose their ability to emit coherently due to the curvature of the field lines.2.Relativistic plasma emission is a multistage emission process involving the generation of plasma turbulence and the partial conversion of this turbulence into escaping radiation. In pulsars the dispersion characteristics of the relativistic electron-positron plasma determines the form of the turbulence, which may be in either longitudinal waves or Alfvèn-like waves. Various instabilities have been suggested to produce turbulence, and a streaming instability is one possibility. Alternatively, in a detailed model proposed by Beskin et al. (1988) the instability depends intrinsically on the curvature of the field lines, and in a theory discussed by Kazbegi et al. (1988), a cyclotron instability generates the turbulence relatively far from the neutron star.3.Free electron maser emission or linear acceleration emission requires an oscillating electric field, postulated to be due to a large amplitude electrostatic wave. A recent analysis of this mechanism (Rowe 1992) shows that it allows emission in two different regimes that provide a possible basis for the interpretation of core and conal emission in pulsars. Effective maser emission seems to require Lorentz factors smaller than other constraints allow.Other suggested theories for the emission mechanism include one that arises from a loophole in the proof that curvature absorption cannot be negative, and another that involves a closed “electrosphere” in which the radio emission is attributed to emission by bunches formed as a result of pair production due to a primary charge accelerated towards the star by its Coulomb field.

Relativistic electron-positron beam formation in the framework of the two-flow model for active galactic nuclei

A model is proposed for relativistic beam formation in active galactic nuclei, in which electrons and positrons are generated by pair cascade on the UV photons of the accretion disk. In situ turbulent acceleration by Alfven waves in a pair plasma balances the Compton losses and prevents annihilation. The origin of the turbulence is in the subrelativistic MHD accretion ejection flow, which guarantees an extended energy reservoir up to distance level, easily achieved, the pair creation becomes catastrophic, and so the dramatic increase of the relativistic pressure expels the pair plasma along the widening flux tubes.