Relativistic Electron-positron Research Articles

Nonlinear Langmuir structures: Soliton and shock in a rotating weakly relativistic electron-positron magnetoplasma with stationary positive ions

Theoretical and numerical studies are performed for nonlinear Langmuir structures (soliton and shock) in a rotating weakly relativistic electron-positron magnetoplasma with background stationary positive ions. For this purpose, the reductive perturbation technique is employed to the weakly relativistic hydrodynamical electrons/positrons fluid equations and Poisson equation, obtaining extended Zakharov–Kuznetsov equation. The latter has been solved analytically. The features of the nonlinear excitations and their propagation conditions are investigated numerically. Our finding could elucidate the nonlinear electrostatic structures that propagate in astrophysical plasma situations where rotating, magnetized plasma can exist; such as polar cups region of pulsars, around active galactic nuclei, neutron stars, and white dwarfs.

Circularly polarized wave propagation in magnetofluid dynamics for relativistic electron-positron plasmas

The dispersion relation for circularly polarized electromagnetic waves propagating in the direction of an external magnetic field in a relativistic electron-positron plasma with arbitrary constant drift velocities is obtained for constant temperature in the homentropic regime. This result is an exact solution of the nonlinear magnetofluid unification field formalism introduced by S. Mahajan [Phys. Rev. Lett. 90, 035001 (2003)], where the electromagnetic and fluid fields are coupled through the relativistic enthalpy density. The behavior of electromagnetic and Alfvén branches of the dispersion relation are discussed for different temperatures.

Ion acoustic shock waves in a relativistic electron–positron–ion plasmas

The Korteweg–de Vries–Burger (KdVB) equation is derived for ion acoustic shock waves in a weakly relativistic electron–positron–ion plasma. Electrons, positrons are considered isothermal and ions are relativistic. The travelling wave solution has been acquired by employing the tangent hyperbolic method. The vivid display of the graphical results is presented and analyzed. It is observed that amplitude and steepness of the shock wave decrease with increase of the relativistic streaming factor, the positron concentration and they increase with the increase of the coefficient of kinematic viscosity and vice versa. It is determined that at low temperature the shock wave propagates, whereas at very high temperature the solitary wave propagates in the system. The results may have relevance in astrophysical plasmas as well as in inertial confinement fusion plasmas.

Positronium in a cavity in a high-Tc superconductor

The behavior of positronium localized in a microvoid in a high-temperature superconductor (HTSC) environment is examined. The interaction of such a positronium with conduction electrons is treated as arising from the Ps ↔ e+ + e− process, which is mathematically described here in terms of the well-known Anderson model for a magnetic impurity in a normal metal. In this model, the interaction underlying this process is due to the positronium state hybridization with the states of conduction elections and the state of the positronium remaining within the void. Similarly to the case of a magnetic impurity, the density of states of an interacting positronium exhibits a 'Kondo resonance' if the Fermi liquid surrounding the void is in the normal state. Based on experimental data on the lifetime τ2 of void-trapped positrons, it is concluded that the hybridization interaction is much stronger than the intra-atomic relativistic electron–positron interaction in the Ps atom. The model used to describe the interacting Ps atom provides a relation between the experimental values of τ2(T) and the properties of the electronic structure of the metal. Experimental results for ceramic HTSC samples of (Bi,Pb)2Sr2Ca2Cu3O7 and (Bi,Pb)-2223 are interpreted, which show a sharp decrease in τ2(T) at T = Tc, where Tc is the superconducting transition temperature. Using the adopted model, some conclusions are drawn as to how the properties of the pseudogap correlate with the experimental τ2(T) dependence observed in (Bi,Pb)-2223 for T > Tc.

WEIBEL INSTABILITY AND ASSOCIATED STRONG FIELDS IN A FULLY THREE-DIMENSIONAL SIMULATION OF A RELATIVISTIC SHOCK

Plasma instabilities (e.g., Buneman, Weibel and other two-stream instabilities) excited in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a new 3-D relativistic particle-in-cell code, we have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. The simulation has been performed using a long simulation system in order to study the nonlinear stages of the Weibel instability, the particle acceleration mechanism, and the shock structure. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic (HD) like shock structure. In the leading shock, electron density increases by a factor of 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. We discuss the possible implication of our simulation results within the AGN and GRB context.

Particle Acceleration in the Driven Relativistic Reconnection

We study the compression driven magnetic reconnection in the relativistic electron-positron plasma. Making use of a 2.5D particle-in-cell code, we simulated compression of a magnetized plasma layer containing a current sheet within it. We found that the particle spectrum within the reconnecting sheet becomes non-thermal; it could be approximated by a power-law distribution with an index of -1 and an exponential cutoff.

Head-on collision of ion-acoustic solitary waves in a weakly relativistic electron–positron–ion plasma

The head-on collision of two ion-acoustic solitary waves in a weakly relativistic electron–positron–ion plasma is studied. By using the extended Poincaré–Lighthill–Kuo perturbation method, we obtain the KdV equations, the analytical phase shifts and the trajectories after the head-on collision of two solitary waves in this three-component plasma. The effects of the ratio of electron temperature to positron temperature, the ratio of the number density of positrons to that of electrons and the relativistic factor on the phase shifts are studied. It is found that these parameters can significantly influence the phase shifts of the solitary waves. Moreover, there are compressive solitary waves in such a system.

Suppression of resistive hose instability in a relativistic electron–positron flow

This paper presents the effects of electron-positron pair production on the linear growth of the resistive hose instability of a filamentary beam that could lead to snake-like distortion. For both the rectangular radial density profile and the diffuse profile reflecting the Bennett-type equilibrium for a self-collimating flow, the modified eigenvalue equations are derived from a Vlasov-Maxwell equation. While for the simple rectangular profile, current perturbation is localized at the sharp radial edge, for the realistic Bennett profile with an obscure edge, it is non-locally distributed over the entire beam, removing catastrophic wave-particle resonance. The pair production effects likely decrease the betatron frequency, and expand the beam radius to increase the resistive decay time of the perturbed current; these also lead to a reduction of the growth rate. It is shown that, for the Bennett profile case, the characteristic growth distance for a preferential mode can exceed the observational length-scale of astrophysical jets. This might provide the key to the problem of the stabilized transport of the astrophysical jets including extragalactic jets up to Mpc ($\sim 3\times 10^{24}$ cm) scales.

All the Astrophysical Jet Sources: Driven by Mono-energetic e ± Beams?

Gopal Krishna and I are now considering E × B-drifting jets since some 25 years, and are still convinced that they form the only consistent description of the huge body of observations. New is our 2004 tightening that (all) the jets consist of mono-energetic flows of extremely relativistic electron-positron pairs, of bulk Lorentz factor γ 104, moving in equipartition with their frozen-in magnetic and electric fields. Whenever their supersonic propagation gets blocked by some (heavy) obstacle, their frozen-in Poynting flux converts the delta-shaped particle-energy distribution into an almost white (in power) power law: E2NE ~ E− with 0.

Simulation study of jitter radiation associated with afterglows observed with Swift

Using a 3D Relativistic Particle-In-Cell (RPIC) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma without initial magnetic fields in order to investigate the nonlinear stage of the Weibel instability. The growth time and nonlinear saturation levels depend on the initial jet parallel velocity distributions. Simulations show that the Weibel instability created in the collisionless shocks accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The nonlinear fluctuation amplitude of densities. currents, electric, and magnetic fields in the electron-positron shocks are larger for smaller jet Lorentz factor. This comes from the fact that. the growth time of the Weibel instability is proportional to the square of tlie jet Lorentz factor. We have performed simulations with broad Lorentz factor distribution of jet electrons and positrons, which are assumed to be created by tlie photon annihilation. Simulation results show that tlie Weibel instability is responsible for generating and amplifying nonuniform, magnetic fields perpendicular to tlie jet propagation direction and contribute to the electron's (positron's) transverse deflection behind the jet head. This small-scale magnetic-field structure is appropriate to the generation of radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation resulting from small-scale magnetic-field structures may be important for understanding the complex time structure anti spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets anti relativistic collisionless sliocks.

Self-guiding electromagnetic beams in relativistic electron–positron plasmas

Nonlinear interaction of an intense electromagnetic (EM) beam with relativistically hot electron–positron plasma is investigated by invoking the variational principle and numerical simulation, resting on the model of generalized nonlinear Schrödinger equation with saturating nonlinearity. The present analysis shows the dynamical properties including the possibilities of trapping and wave-breaking of EM beams. These properties of EM beams may give a significant clue for the gamma-ray burst.

Generation of magnetic field fluctuations in relativistic electron–positron magnetoplasmas

It is shown that magnetic field aligned equilibrium relativistic plasmas flows can excite electromagnetic fluctuations in a magnetized electron–positron (e–p) plasma. For this purpose, a new disper ...

Ion-acoustic solitons in weakly relativistic plasma containing electron–positron and ion

The ion-acoustic solitons in a weakly relativistic electron–positron–ion plasma have been investigated. Such plasmas frequently occur in some astrophysical environment. We have used the reductive perturbation method (RPM) to study the characteristic of ion-acoustic solitary waves in this three component plasma. The KdV equation derived by RPM is solved and its solitonic behavior is studied as a function of number of parameters like densities of electron and positron, relative temperature ratio of electron to positron and relativistic factor. We have observed that these parameters significantly influence the peak amplitude and width of the solitons. Only compressive solitons are obtained. No double layers in the given parameter regime are possible.

Relativistic Landau damping of longitudinal waves in isotropic pair plasmas

Landau damping is described in relativistic electron-positron plasmas. Relativistic electron-positron plasma theory contains important new effects when compared with classical plasmas. For example, there are undamped superluminal wave modes arising from both a continuous and discrete mode structure, the former even in the classical limit. We present here a comprehensive analytical treatment of the general case resulting in a compact and useful form for the dispersion relation. The classical pair-plasma case is addressed, for completeness, in an appendix.

A Physical Model for Active Galactic Nuclei with Double‐peaked Broad Emission Lines

The double-peaked broad emission lines are usually thought to be linked to accretion disks; however, the local viscous heating in the line-emitting disk portion is usually insufficient for the observed double-peaked broad-line luminosity in most sources. It was suggested that the X-ray radiation from an ion-supported torus in the inner region of the disk can photoionize the outer line-emitting disk region. However, our calculations show that only a small fraction (≲2.3%) of the radiation from the radiatively inefficient accretion flow (RIAF) in the inner region of the disk can photoionize the line-emitting disk portion, because the solid angle of the outer disk portion subtended to the inner region of the RIAF is too small. We propose a physical model for double-peaked line emitters, in which only those AGNs with sufficient matter above the disk (slowly moving jets or outflows) can scatter enough photons radiated from the inner disk region to the outer line-emitting disk portion extending from several hundred to more than 2000 gravitational radii. Our model predicts a power-law r-dependent line emissivity Hα ∝ R, where β ~ 2.5, which is consistent with β ~ 2-3 required by the model fittings for double-peaked line profiles. Using a sample of radio-loud AGNs with double-peaked emission lines, we show that the outer disk regions can be efficiently illuminated by the photons scattered from slow or mild relativistic electron-positron jets with γj ≲ 2. It is consistent with the fact that no double-peaked emission line is present in strong radio quasars with relativistic jets. For radio-quiet double-peaked line emitters, slow outflows with Thomson scattering depth ~ 0.2 instead of jets can scatter sufficient photons to (illuminate) the line-emitting regions. This model can therefore solve the energy budget problem for double-peaked line emitters.

Acceleration Mechanics in Relativistic Shocks by the Weibel Instability

Plasma instabilities (e.g., Buneman, Weibel, and other two-stream instabilities) created in collisionless shocks may be responsible for particle (electron, positron, and ion) acceleration. Using a three-dimensional relativistic electromagnetic particle code, we have investigated long-term particle acceleration associated with relativistic electron-ion or electron-positron jet fronts propagating into an unmagnetized ambient electron-ion or electron-positron plasma. These simulations have been performed with a longer simulation system than our previous simulations in order to investigate the nonlinear stage of the Weibel instability and its particle acceleration mechanism. The current channels generated by the Weibel instability are surrounded by toroidal magnetic fields and radial electric fields. This radial electric field is quasi stationary and accelerates particles that are then deflected by the magnetic field. Whether particles are accelerated or decelerated along the jet propagation direction depends on the velocity of particles and the sign of × in the moving frame of each particle. For the electron-ion case the large-scale current channels generated by the ion Weibel instability lead to more acceleration near the jet head. Consequently, the accelerated jet electrons in the electron-ion jet have a significant hump above a thermal distribution. However, in the electron-positron case, accelerated jet electrons have a smoother, nearly thermal distribution. In the electron-positron case, initial acceleration occurs as current channels form and then continues at a much lesser rate as the current channels and corresponding toroidal magnetic fields generated by the Weibel instability dissipate.

A unified accretion-ejection paradigm for black hole X-ray binaries

We present a new picture for the central regions of Black Hole X-ray Binaries. In our view, these central regions have a multi-flow configuration which consists in (1) an outer standard accretion disc down to a transition radius rJ; (2) an inner magnetized accretion disc below rJ driving (3) a non relativistic self-collimated electron-proton jet surrounding, when adequate conditions for pair creation are met; (4) a ultra relativistic electron-positron beam. This accretion-ejection paradigm provides a simple explanation to the canonical spectral states, from radio to X/γ-rays, by varying the transition radius rJ and disc accretion rate independently. Large values of rJ correspond to the Quiescent state for low and the Hard state for larger . These states are characterized by the presence of a steady electron-proton MHD jet emitted by the disc below rJ. The hard X-ray component is expected to form at the jet basis. When rI becomes smaller than the marginally stable orbit ri, the whole disc resembles a standard accretion disc with no jet, characteristic of the Soft state. Intermediate states correspond to situations where . At large , an unsteady pair cascade process is triggered within the jet axis, giving birth to flares and ejection of relativistic pair blobs. This would correspond to the luminous intermediate state, sometimes referred to as the Very High state, with its associated superluminal motions. The variation of rJ independently of is a necessary ingredient in this picture. It arises from the presence of a large scale vertical magnetic field threading the disc. Features such as possible hysteresis and the presence of quasi-periodic oscillations would naturally fit within this new framework.

A unified accretion–ejection paradigm for Black Hole X-ray binaries

We present a unified accretion–ejection picture that explains the different spectral state of Black Hole X-ray binaries (BHXrB) from radio to X/γ-rays. In this view, the central region of BHXrB has a multi-flow configuration which consists in (1) an outer standard accretion disc, (2) an inner magnetized accretion disc driving, (3) a self-collimated electron–proton MHD jet, surrounding and (4) a relativistic electron–positron beam when adequate conditions are met. This picture provides a simple and unified explanation to the various canonical spectral states of BH X-ray binaries, by varying the transition radius r J between the inner disc driving jets and the outer standard disc. In this framework, large r J correspond to Quiescent and Hard states while small r J correspond to Thermal Dominant ones. In between these two extremes, r J can reach values that switches on the pair cascade process giving birth to a relativistic electron–positron beam. This would correspond to the bright intermediate state.

Particle Acceleration and Magnetic Field Generation in Electron‐Positron Relativistic Shocks

Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel, and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a three-dimensional relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. New simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. Furthermore, the nonlinear fluctuation amplitudes of densities, currents, and electric and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at a comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. In addition, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by tine Weibel instability scale proportionally to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields, which contribute to the electron s (positron s) transverse deflection behind the jet head. This small- scale magnetic field structure is appropriate to the generation of radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation has different properties than synchrotron radiation calculated assuming a uniform magnetic field. The jitter radiation resulting from small-scale magnetic field structures may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks.

A supermassive binary black hole in the quasar 3C 345

Radio loud active galactic nuclei present a remarkable variety of signs indicating the presence of periodical processes possibly originating in binary systems of supermassive black holes, in which orbital motion and precession are ultimately responsible for the observed broad-band emission variations, as well as for the morphological and kinematic properties of the radio emission on parsec scales. This scenario, applied to the quasar 3C 345, explains the observed variations of radio and optical emission from the quasar, and reproduces the structural variations observed in the parsec-scale jet of this object. The binary system in 3C 345 is described by two equal-mass black holes with masses of ≈7.1 × 10 8 Mseparated by ≈0.33 pc and orbiting with a period ∼480 yr. The orbital motion induces a precession of the accretion disk around the primary black hole, with a period of ≈2570 yr. The jet plasma is described by a magnetized, relativistic electron-positron beam propagating inside a wider and slower electron-proton jet. The combination of Alfven wave perturbations of the beam, the orbital motion of the binary system and the precession of the accretion disk reproduces the variability of the optical flux and evolution of the radio structure in 3C 345. The timescale of quasi-periodic flaring activity in 3C 345 is consistent with typical disk instability timescales. The present model cannot rule out a small-mass orbiter crossing the accretion disk and causing quasi-periodic flares.