Magnetosonic Shock Waves Research Articles

Nonthermal Electrons at High Mach Number Shocks: Electron Shock Surfing Acceleration

We study the suprathermal electron acceleration mechanism in a perpendicular magnetosonic shock wave in a high Mach number regime by using a particle-in-cell simulation. We find that shock surfing/surftron acceleration producing the suprathermal electrons occurs in the shock transition region where a series of large amplitude electrostatic solitary waves (ESWs) are excited by Buneman instability under the interaction between the reflected ions and the incoming electrons. It is shown that the electrons are likely to be trapped by ESWs, and during the trapping phase they can be effectively accelerated by the shock motional/convection electric field. We discuss that suprathermal electrons can be accelerated up to $m_i c^2 (v_0/c)$, where $m_i c^2$ is the ion rest mass energy and $v_0$ is the shock upstream flow velocity. Furthermore, some of these suprathermal electrons may be effectively trapped for infinitely long time when Alfv\'en Mach number $M_A$ exceeds several 10, and they are accelerated up to the shock potential energy determined by the global shock size.

Long time behavior of relativistic ions incessantly accelerated by an oblique shock wave

Incessant acceleration of nonthermal fast ions by an oblique magnetosonic shock wave is studied with hybrid simulations. First, magnetic and electric field profiles of an oblique shock wave are obtained by means of a one-dimensional, relativistic, electromagnetic, particle simulation. Test particle trajectories of fast ions are then calculated using these wave profiles. Some fast ions are trapped by the shock wave owing to the relativistic effect that velocity is limited by the speed of light while the momentum can grow indefinitely. In these simulations, some fast ions are found to suffer energy jumps several tens of times; as a result, their final maximum Lorentz factors far exceeded 100.

Electron acceleration and trapping by an oblique shock wave

Electron acceleration to ultrarelativistic energies by an oblique magnetosonic shock wave is studied. First, the maximum electron energy is analytically obtained with new simple calculations. The physical mechanism is also discussed in detail. In the wave frame, electrons reflected near the end of the main pulse region, which will be trapped, gain energy from the electric potential and constant electric field Ey0 perpendicular to the external magnetic field. For certain plasma parameters, these electrons can move a long distance in the direction of Ey0 and obtain a great amount of energy from Ey0. It is argued that the trapped electrons can hardly escape from the shock wave. Next, one-dimensional, relativistic, particle simulations are carried out. Theoretical estimates such as the maximum electron energy are found to be in good agreement with the simulations. Simulations also show that the number of trapped electrons continually increases with time.

The surfatron acceleration of cosmic rays in the galactic plasma

The optimum conditions for a prolonged holding of charged particles resonantly trapped from the galactic plasma by nonlinear waves and for the acceleration of these particles to high energies by the surfatron mechanism are established. The density of particles trapped by the plasma waves of large amplitude and by the quasitransverse magnetosonic shock waves is estimated. Various reasons leading to possible breakage of the process of surfatron acceleration of cosmic rays in the Galaxy are considered. Within the framework of the surfatron acceleration mechanism, galactic cosmic rays originate predominantly from the interstellar plasma and their energy spectrum is formed in two stages. In the first stage, some of the galactic plasma particles are accelerated from thermal energies to 1015 eV/nucleon; in the second stage, the cosmic rays may continue gaining energy up to 1019 eV/nucleon and above.

Strong Electron Acceleration at High Mach Number Shock Waves: Simulation Study of Electron Dynamics

Electron-ion dynamics in a perpendicular magnetosonic shock wave in a high Mach number regime is studied by using the particle-in-cell simulation. It is shown that in the shock transition layer nonlinear evolution of two-stream instabilities plays an important role on the electron rapid heating and acceleration. As the shock Mach number greatly exceeds the critical Mach number, a series of large-amplitude, coherent electrostatic waves with the electron holes in phase space are excited by the two-stream instability between the reflected ions and the incident electrons in the shock transition layer. As the incident electrons are decelerated by the instability, other electrostatic waves grow in time by another two-stream instability between the incident ions and the decelerated incident electrons. The dynamic timescale of these instabilities is of the order of ω, where ωpe is the plasma frequency. The nonlinear interaction of these waves leads to the strong electron heating as well as the nonthermal high-energy electron acceleration in the shock transition layer.

Energies of ultrarelativistic electrons produced by an oblique shock wave

Production of ultrarelativistic electrons in an oblique magnetosonic shock wave is studied theoretically and numerically. First, the structure of the oblique shock wave is analytically discussed on the basis of a relativistic, two-fluid model. Then, by use of the field strengths thus obtained, the maximum energy of accelerated electrons is calculated as a function of the propagation speed and angle of the shock wave. Next, a one-dimensional, relativistic, electromagnetic, particle simulation code is used to further investigate the shock propagation and associated electron acceleration. Lorentz factors of accelerated electrons can exceed 100. Detailed comparisons are made between the theoretically predicted field strengths and electron energy and those obtained by the simulations.

Generation of electromagnetic waves in the electron-positron plasma in the vicinity of a pulsar

The problem of the efficiency of the ion-synchrotron maser proposed by Hoshino and Arons is analyzed in a linear approximation. A hot, relativistic, electron-positron plasma penetrated by a relativistic ion beam is considered. At the front of the magnetosonic shock wave an electromagnetic wave is generated, which should be damped on positrons of the plasma. This should, in turn, result in synchrotron emission from energetic positrons in the high-frequency range, far above the natural frequencies of the plasma. It is shown that one must allow simultaneously for the conditions of resonance at a high harmonic of the ion-cyclotron frequency and at the fundamental of the electron-cyclotron frequency. Natural transverse waves are generated in the process, but within the framework of the linear theory there is no positron acceleration due to the kinetic energy of ions.

Simulation of the formation of accelerating structures and ion acceleration in the collision of magnetosonic shock waves

Results are presented from numerical calculations of the maximum energy of accelerated deuterons as a function of the magnetic field for two models of the formation of the accelerating field in the region where two magnetosonic shock waves collide. The numerical results are compared with the similar experimental dependence.

Effect of the magnetic field on the energy of deuterium ions accelerated in the collision of magnetosonic shock waves

A study is made of the effect of the initial magnetic field magnitude on the energy of deuterium ions accelerated in the collision of two magnetosonic shock waves propagating in a deuterium plasma quasi-perpendicularly to the magnetic field. Experiments were carried out at a constant plasma density of ⋍2.5×1013 cm−3. It is found that, as the external magnetic field decreases from 1.4 to 0.7 T and, accordingly, the magnetic Mach number increases from 1.02 to 2.3, the energy of accelerated ions increases from 3.2 to 7.5 MeV. The maximum number of accelerated ions attains 105–106 particles per shot.

Production of Ultrarelativistic Electrons by Oblique Magnetosonic Shock Waves

Electron motion in an oblique magnetosonic wave is studied by means of a one-dimensional, relativistic, electromagnetic particle code with full ion and electron dynamics. It is found that high-energy electrons can be produced; electrons with Lorentz factors γ> 100 have been observed in the simulations. They are reflected and then trapped by the wave. This phenomenon occurs in a large-amplitude oblique shock in a strong magnetic field such that \(\omega_{\rm ce} \gtrsim \omega_{\rm pe}\). The acceleration mechanism is given, and the dependence of γ on plasma parameters, such as the propagation angle, is discussed.

Relaxation of the shock wave‐reflected ion beam, and generation of hot electrons

The results obtained with the collisionless shock wave (CSW) experiments on a laboratory device are presented. Ion beam relaxation regimes both in the region of main jump of the magnetic field (“ramp”) and in the zone occupied by the reflected ion flux are grouped into classes. Ahead of the magnetic front a reflecting hump of the electrostatic potential was recorded, which was formed by the ion beam reflected by potential jump in the magnetic ramp region. An electron acceleration effect in the ion‐ion interaction region ahead of the magnetic front to energies of about 100 initial electron temperatures was detected. Hot electrons propagate anomalously rapidly from this region across the magnetic field in the form of a localized disturbance. In the neighborhood of the ion reflection zone in the ramp region, a nonadiabatic heating of electrons to energies approaching the value of the electrostatic potential within the CSW was detected. Analysis of experimental results suggests that (1) the shock front structure is not in steady state and (2) the transverse magnetosonic shock wave in a collisionless plasma has the following common structural characteristics: hot electron region‐turbulent region, occupied by the reflected ion flux‐diffusion magnetic foot‐jump of plasma parameters and the magnetic field (ramp region)‐relaxation region behind the shock front. Implications of experimental results obtained in this study to the Earth's magnetosphere physics are discussed.

Ion Motions in Magnetosonic Shock Waves with Relativistic Propagation Speeds

Ion motions in shock waves propagating perpendicular to a magnetic field are studied through theory and simulation; the shocks with relativistic propagation speeds are considered. In such shocks the longitudinal electric fields are less important than in nonrelativistic ones. From the analysis of ion orbits it is found that ion velocities parallel to the wave front can be comparable to the shock propagation speed v sh in the pulse region. Expressions for ion energies, which can be relativistic, are given as a function of the shock propagation speed. Then, simulations of shock waves are performed by use of a one-dimensional, relativistic, electromagnetic particle code with full ion and electron dynamics. The shock speeds in the simulations were in the range 0.5 ≤ v sh / c ≤0.9. The simulation results on ion orbits and energies are compared in detail with the theory.

Pulsar Winds

AbstractThe shock excitation of pulsar powered nebulae (plerions) is discussed, based on recent theoretical work on the structure of relativistic, collisionless magnetosonic shock waves. This theory is used to outline a model in which theγ−2injection spectrum of the Crab Nebula is satisfactorily accounted for. The same theory suggests a model of the “wisp” features in the Crab Nebula which accounts for these time variable features in the surface bightness as compressions associated with the magnetic overshootswithinthe shock structure. It is pointed out that this theory suggests observable variability in the high energy gamma rays from the Crab Nebula (ε > 50 MeV).

The Corrugation Instability in Slow Magnetosonic Shock Waves

The Corrugation Instability in Slow Magnetosonic Shock Waves

Formation of non-thermal, high energy particles in relativistic magnetosonic shock waves

We study the kinetic nature of the relativistic, perpendicular shocks in electron-ion plasmas and discuss the origin of non-thermal high energy particles, using the full particle simulation code including the relativistic Lorentz equation. We find that the electron can be accelerated up to the upstream ion kinetic energy in the form of non-thermal high energy tail.

Shock waves in the solar corona and their radio emission

In the solar corona shock waves can be generated by coronal mass ejections and/or solar flares. They manifest themselves in solar type II radio bursts. A sample of 25 such radio bursts is investigated concerning their spectral features. Assuming that the type II burst radiation is generated in the vicinity of the transition region of coronal shock waves as indicated by plasma wave measurements at interplanetary shock waves the instantaneous bandwidth reflects the density jump of the shock. Comparing the observational results with the evaluation of the Rankine-Hugoniot relations of MHD shock waves solar type II bursts should be regarded as being generated by weak supercritical, quasi-parallel fast magnetosonic shock waves in the solar corona. As well-known from Earth's bow shock, quasi-parallel collisionless shocks are associated by strong magnetic field turbulence, e.g., in form of short large amplitude magnetic field structures (SLAMS). Assuming that these features also appear at quasi-parallel shock waves in the solar corona, electrons can be accelerated at such shock waves due to drift acceleration within SLAMS up to suprathermal energies. These electrons are able to excite Langmuir waves which can convert into radio waves observed as solar type II bursts.

WKB approach to the problem of MHD shock propagation through the heliospheric current sheet

The interplanetary shock wave front shape and intensity are calculated numerically by means of the WKB-approach, with nonlinear effects taken into account. The solar flare is modelled as an isotropic point explosion at the solar wind base. The heliospheric current sheet (HCS) is represented by a radially diverging stream with a higher plasma concentration and a lower wind speed. Fast magnetosonic shock wave propagation along the HCS is connected with the effect of regular accumulation of the wave energy in the vicinity of the HCS. In this place the wave intensity is increased, and the corresponding front fragments go ahead to form a shock-wave forerunner as a ‘pimple’. The ‘primple’, in turn, is located inside a quite a large, but less-contrast, ‘dimple’ in the wave surface. This ‘dimple’ approximately coincides with the HCS stream contours. If the flare is outside the HCS boundaries, the picture discussed above is conserved, but asymmetry effects arise. Thus the interplanetary shock is stronger when the Earth's observer and the flare are on the same side of the HCS and is weaker in the opposite case.

Formation of fast magnetosonic shock waves during a two-current-loop collision in solar flares

We present a numerical simulation of the fast magnetosonic shock wave formation during a two-current-loop collision by using a magnetohydrodynamical model. It is shown that the rarefaction waves are generated in the initial stage when the two current loops start to collide. After the rarefaction waves propagate away from the excited region, the fast magnetosonic waves with density enhancement can be produced for the simulation when the current strength of the loop is weak. As the current becomes strong enough, the magnetosonic shock waves can be generated in the direction perpendicular to that of the two-loop collision.

Relativistic magnetosonic shock waves in synchrotron sources - Shock structure and nonthermal acceleration of positrons

view Abstract Citations (336) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Relativistic Magnetosonic Shock Waves in Synchrotron Sources: Shock Structure and Nonthermal Acceleration of Positrons Hoshino, Masahiro ; Arons, Jonathan ; Gallant, Yves A. ; Langdon, A. B. Abstract The theoretical properties of relativistic, transverse, magnetosonic collisionless shock waves in electron-positron-heavy ion plasmas of relevance to astrophysical sources of synchrotron radiation are investigated. Both 1D electromagnetic particle-in-cell simulations and quasi-linear theory are used to examine the spatial and kinetic structure of these nonlinear flows. A new process of shock acceleration of nonthermal positrons, in which the gyrating reflected heavy ions dissipate their energy in the form of collectively emitted, left-handed magnetosonic waves which are resonantly absorbed by the positrons immediately behind the ion reflection region, is described. Applications of the results to the termination shocks of pulsar winds and to the termination shocks of jets emanating from the AGN are outlined. Publication: The Astrophysical Journal Pub Date: May 1992 DOI: 10.1086/171296 Bibcode: 1992ApJ...390..454H Keywords: Crab Nebula; Cyclotron Radiation; Interstellar Matter; Particle Acceleration; Positrons; Pulsars; Shock Waves; Synchrotron Radiation; Computational Astrophysics; Electron-Positron Pairs; Energy Spectra; Magnetosonic Resonance; Numerical Analysis; Radio Jets (Astronomy); Relativistic Particles; Astrophysics; ACCELERATION OF PARTICLES; GALAXIES: JETS; ISM: INDIVIDUAL NAME: CRAB NEBULA; STARS: PULSARS: GENERAL; RADIATION MECHANISMS: CYCLOTRON AND SYNCHROTRON; SHOCK WAVES full text sources ADS | data products SIMBAD (2)

Relativistic Shock Waves and the Excitation of Plerions

AbstractThe shock termination of a relativistic magnetohydrodynamic wind from a pulsar is the most interesting and viable model for the excitation of the synchrotron sources observed in plerionic supernova remnants. We have studied the structure of relativistic magnetosonic shock waves in plasmas composed purely of electrons and positrons, as well as those whose composition includes heavy ions as a minority constituent by number. We find that relativistic shocks in symmetric pair plasmas create fully thermalized distributions of particles and fields downstream. Therefore, such shocks are not good candidates for the mechanism which converts rotational energy lost from a pulsar into the nonthermal synchrotron emission observed in plerions. However, when the upstream wind contains heavy ions which are a minority constituent by number density, but carry the bulk of the energy density, much of the energy of the shock goes into a downstream, nonthermal power-law distribution of positrons with energy distribution N(E)dE ∝ E–s. In a specific model presented in some detail, s = 3. These characteristics are close to those assumed for the pairs in macroscopic MHD wind models of plerion excitation. The essential mechanism is collective synchrotron emission of left-handed extraordinary modes by the ions in the shock front at high harmonics of the ion-cyclotron frequency, with the downstream positrons preferentially absorbing almost all of this radiation, mostly at their fundamental (relativistic) cyclotron frequencies. Possible applications to the models of plerions and to constraints on theories of energy loss from pulsars are briefly outlined.