scholarly journals PARTICLE ACCELERATION AT THE TERMINATION SHOCK OF STRIPED PULSAR WINDS

2012 ◽  
Vol 08 ◽  
pp. 144-150 ◽  
Author(s):  
LORENZO SIRONI ◽  
ANATOLY SPITKOVSKY
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Magnetic Energy ◽  
Termination Shock ◽  
Larmor Radius ◽  
Pulsar Wind Nebulae ◽  
Field Polarity ◽  
Particle In Cell ◽  
Post Shock ◽  
Pulsar Wind

The relativistic wind of pulsars consists of toroidal stripes of opposite magnetic field polarity, separated by current sheets of hot plasma. By means of multi-dimensional particle-in-cell simulations, we investigate particle acceleration and magnetic field dissipation at the termination shock of a relativistic striped pulsar wind. At the shock, the flow compresses and the alternating fields annihilate by driven magnetic reconnection. Irrespective of the stripe wavelength λ or the wind magnetization σ (in the regime σ ≫1 of magnetically dominated flows), shock-driven reconnection transfers all the magnetic energy of alternating fields to the particles. In the limit λ/(rL σ) ≫ 1, where rL is the relativistic Larmor radius in the wind, the post-shock spectrum approaches a flat power-law tail with slope around -1.5, populated by particles accelerated by the reconnection electric field. Our findings place important constraints on the models of non-thermal radiation from Pulsar Wind Nebulae.

scholarly journals Lepton-driven Nonresonant Streaming Instability

2021 ◽  
Vol 923 (2) ◽  
pp. 208
Author(s):  
Siddhartha Gupta ◽  
Damiano Caprioli ◽  
Colby C. Haggerty
Keyword(s):  
Magnetic Field ◽  
Laboratory Experiments ◽  
Magnetized Plasma ◽  
Ion Current ◽  
Pulsar Wind Nebulae ◽  
Particle In Cell ◽  
Streaming Instability ◽  
Electrons And Positrons ◽  
Pulsar Wind ◽  
The Magnetic Field

Abstract A strong super-Alfvénic drift of energetic particles (or cosmic rays) in a magnetized plasma can amplify the magnetic field significantly through nonresonant streaming instability (NRSI). While the traditional analysis is done for an ion current, here we use kinetic particle-in-cell simulations to study how the NRSI behaves when it is driven by electrons or by a mixture of electrons and positrons. In particular, we characterize the growth rate, spectrum, and helicity of the unstable modes, as well the level of the magnetic field at saturation. Our results are potentially relevant for several space/astrophysical environments (e.g., electron strahl in the solar wind, at oblique nonrelativistic shocks, around pulsar wind nebulae), and also in laboratory experiments.

scholarly journals Studying particle acceleration from driven magnetic reconnection at the termination shock of a relativistic striped wind using particle-in-cell simulations

2020 ◽  
Vol 235 ◽  
pp. 07003
Author(s):  
Yingchao Lu ◽  
Fan Guo ◽  
Patrick Kilian ◽  
Hui Li ◽  
Chengkun Huang ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Magnetic Reconnection ◽  
Magnetic Energy ◽  
Maximum Energy ◽  
Termination Shock ◽  
Particle In Cell ◽  
Poynting Flux ◽  
Electrons And Positrons ◽  
Particle Kinetic Energy ◽  
Fermi Type

A rotating pulsar creates a surrounding pulsar wind nebula (PWN) by steadily releasing an energetic wind into the interior of the expanding shockwave of supernova remnant or interstellar medium. At the termination shock of a PWN, the Poynting-flux- dominated relativistic striped wind is compressed. Magnetic reconnection is driven by the compression and converts magnetic energy into particle kinetic energy and accelerating particles to high energies. We carrying out particle-in-cell (PIC) simulations to study the shock structure as well as the energy conversion and particle acceleration mechanism. By analyzing particle trajectories, we find that many particles are accelerated by Fermi-type mechanism. The maximum energy for electrons and positrons can reach hundreds of TeV.

scholarly journals A corrugated termination shock in pulsar wind nebulae?

2016 ◽  
Vol 82 (4) ◽  
Author(s):  
Martin Lemoine
Keyword(s):  
Magnetic Field ◽  
Crab Nebula ◽  
Radiation Reaction ◽  
Termination Shock ◽  
Pulsar Wind Nebulae ◽  
Order Unity ◽  
Poynting Flux ◽  
Electron Positron ◽  
Pulsar Wind ◽  
The Crab Nebula

Successful phenomenological models of pulsar wind nebulae assume efficient dissipation of the Poynting flux of the magnetized electron–positron wind as well as efficient acceleration of the pairs in the vicinity of the termination shock, but how this is realized is not yet well understood. This paper suggests that the corrugation of the termination shock, at the onset of nonlinearity, may lead towards the desired phenomenology. Nonlinear corrugation of the termination shock would convert a fraction of order unity of the incoming ordered magnetic field into downstream turbulence, slowing down the flow to sub-relativistic velocities. The dissipation of turbulence would further preheat the pair population on short length scales, close to equipartition with the magnetic field, thereby reducing the initial high magnetization to values of order unity. Furthermore, it is speculated that the turbulence generated by the corrugation pattern may sustain a relativistic Fermi process, accelerating particles close to the radiation reaction limit, as observed in the Crab nebula. The required corrugation could be induced by the fast magnetosonic modes of downstream nebular turbulence; but it could also be produced by upstream turbulence, either carried by the wind or seeded in the precursor by the accelerated particles themselves.

scholarly journals A global model of particle acceleration at pulsar wind termination shocks

2020 ◽  
Vol 642 ◽  
pp. A123
Author(s):  
Benoît Cerutti ◽  
Gwenael Giacinti
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Shock Front ◽  
Large Scale ◽  
Particle Accelerators ◽  
Global Dynamics ◽  
Pulsar Wind Nebulae ◽  
Current Sheets ◽  
Pulsar Wind ◽  
Downstream Flow

Context. Pulsar wind nebulae are efficient particle accelerators, and yet the processes at work remain elusive. Self-generated, microturbulence is too weak in relativistic magnetized shocks to accelerate particles over a wide energy range, suggesting that the global dynamics of the nebula may be involved in the acceleration process instead. Aims. In this work, we study the role played by the large-scale anisotropy of the transverse magnetic field profile on the shock dynamics. Methods. We performed large two-dimensional particle-in-cell simulations for a wide range of upstream plasma magnetizations, from weakly magnetized to strongly magnetized pulsar winds. Results. The magnetic field anisotropy leads to a dramatically different structure of the shock front and downstream flow. A large-scale velocity shear and current sheets form in the equatorial regions and at the poles, where they drive strong plasma turbulence via Kelvin-Helmholtz vortices and kinks. The mixing of current sheets in the downstream flow leads to efficient nonthermal particle acceleration. The power-law spectrum hardens with increasing magnetization, akin to those found in relativistic reconnection and kinetic turbulence studies. The high end of the spectrum is composed of particles surfing on the wake produced by elongated spearhead-shaped cavities forming at the shock front and piercing through the upstream flow. These particles are efficiently accelerated via the shear-flow acceleration mechanism near the Bohm limit. Conclusions. Magnetized relativistic shocks are very efficient particle accelerators. Capturing the global dynamics of the downstream flow is crucial to understanding them, and therefore local plane parallel studies may not be appropriate for pulsar wind nebulae and possibly other astrophysical relativistic magnetized shocks. A natural outcome of such shocks is a variable and Doppler-boosted synchrotron emission at the high end of the spectrum originating from the shock-front cavities, reminiscent of the mysterious Crab Nebula gamma-ray flares.

scholarly journals The formation of relativistic plasma structures and their potential role in the generation of cosmic ray electrons

2008 ◽  
Vol 15 (6) ◽  
pp. 831-846 ◽  
Author(s):  
M. E. Dieckmann
Keyword(s):  
Magnetic Field ◽  
Phase Space ◽  
Magnetic Energy ◽  
Ion Beam ◽  
Cosmic Ray ◽  
Compact Objects ◽  
Space Structures ◽  
Magnetic Field Generation ◽  
Particle In Cell ◽  
Field Generation

Abstract. Recent particle-in-cell (PIC) simulation studies have addressed particle acceleration and magnetic field generation in relativistic astrophysical flows by plasma phase space structures. We discuss the astrophysical environments such as the jets of compact objects, and we give an overview of the global PIC simulations of shocks. These reveal several types of phase space structures, which are relevant for the energy dissipation. These structures are typically coupled in shocks, but we choose to consider them here in an isolated form. Three structures are reviewed. (1) Simulations of interpenetrating or colliding plasma clouds can trigger filamentation instabilities, while simulations of thermally anisotropic plasmas observe the Weibel instability. Both transform a spatially uniform plasma into current filaments. These filament structures cause the growth of the magnetic fields. (2) The development of a modified two-stream instability is discussed. It saturates first by the formation of electron phase space holes. The relativistic electron clouds modulate the ion beam and a secondary, spatially localized electrostatic instability grows, which saturates by forming a relativistic ion phase space hole. It accelerates electrons to ultra-relativistic speeds. (3) A simulation is also revised, in which two clouds of an electron-ion plasma collide at the speed 0.9c. The inequal densities of both clouds and a magnetic field that is oblique to the collision velocity vector result in waves with a mixed electrostatic and electromagnetic polarity. The waves give rise to growing corkscrew distributions in the electrons and ions that establish an equipartition between the electron, the ion and the magnetic energy. The filament-, phase space hole- and corkscrew structures are discussed with respect to electron acceleration and magnetic field generation.

scholarly journals Fast magnetic energy dissipation in relativistic plasma induced by high order laser modes

2016 ◽  
Vol 4 ◽  
Author(s):  
Y. J. Gu ◽  
Q. Yu ◽  
O. Klimo ◽  
T. Zh. Esirkepov ◽  
S. V. Bulanov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Magnetic Energy ◽  
Collisionless Plasma ◽  
High Energy ◽  
Field Energy ◽  
Displacement Current ◽  
Particle In Cell ◽  
Magnetic Field Energy ◽  
High Energy Electrons

Fast magnetic field annihilation in a collisionless plasma is induced by using TEM(1,0) laser pulse. The magnetic quadrupole structure formation, expansion and annihilation stages are demonstrated with 2.5-dimensional particle-in-cell simulations. The magnetic field energy is converted to the electric field and accelerate the particles inside the annihilation plane. A bunch of high energy electrons moving backwards is detected in the current sheet. The strong displacement current is the dominant contribution which induces the longitudinal inductive electric field.

scholarly journals Kinetic ‘jets’ from fast-moving pulsars

2019 ◽  
Vol 485 (2) ◽  
pp. 2041-2053 ◽  
Author(s):  
Maxim V Barkov ◽  
Maxim Lyutikov ◽  
Noel Klingler ◽  
Pol Bordas
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Interstellar Medium ◽  
Fast Moving ◽  
Thermal Emission ◽  
Pulsar Wind Nebulae ◽  
Ambient Magnetic Field ◽  
Ram Pressure ◽  
Pulsar Wind ◽  
Ism Magnetic Fields

AbstractSome fast-moving pulsars, such as the Guitar and the Lighthouse, exhibit asymmetric non-thermal emission features that extend well beyond their ram pressure confined pulsar wind nebulae (PWNe). Based on our 3D relativistic simulations, we analytically explain these features as kinetically streaming pulsar wind particles that escaped into the interstellar medium (ISM) due to reconnection between the PWN and ISM magnetic fields. The structure of the reconnecting magnetic fields at the incoming and outgoing regions produces highly asymmetric magnetic bottles therefore and result in asymmetric extended features. For the features to become visible, the ISM magnetic field should be sufficiently high, BISM > 10 $\mu$G. We also discuss archival observations of PWNe displaying evidence of kinetic jets: the Dragonfly PWN (PSR J2021 + 3651), G327.1–1.1, and MSH 11–62, the latter two of which exhibit symmetric ‘snail eyes’ morphologies. We suggest that in those cases the pulsar is moving along the ambient magnetic field in a frisbee-type configuration.

scholarly journals Alfvén wave interaction with inhomogeneous plasmas: acceleration and energy cascade towards small-scales

2004 ◽  
Vol 22 (6) ◽  
pp. 2081-2096 ◽  
Author(s):  
V. Génot ◽  
P. Louarn ◽  
F. Mottez
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Waves ◽  
Wave Interaction ◽  
Skin Depth ◽  
Alfven Wave ◽  
Double Layers ◽  
Larmor Radius ◽  
Density Gradients ◽  
Particle In Cell ◽  
The Magnetic Field

Abstract. Investigating the process of electron acceleration in auroral regions, we present a study of the temporal evolution of the interaction of Alfvén waves (AW) with a plasma inhomogeneous in a direction transverse to the static magnetic field. This type of inhomogeneity is typical of the density cavities extended along the magnetic field in auroral acceleration regions. We use self-consistent Particle In Cell (PIC) simulations which are able to reproduce the full nonlinear evolution of the electromagnetic waves, as well as the trajectories of ions and electrons in phase space. Physical processes are studied down to the ion Larmor radius and electron skin depth scales. We show that the AW propagation on sharp density gradients leads to the formation of a significant parallel (to the magnetic field) electric field (E-field). It results from an electric charge separation generated on the density gradients by the polarization drift associated with the time varying AW E-field. Its amplitude may reach a few percents of the AW E-field. This parallel component accelerates electrons up to keV energies over a distance of a few hundred Debye lengths, and induces the formation of electron beams. These beams trigger electrostatic plasma instabilities which evolve toward the formation of nonlinear electrostatic structures (identified as electron holes and double layers). When the electrostatic turbulence is fully developed we show that it reduces the further wave/particle exchange. This sequence of mechanisms is analyzed with the program WHAMP, to identify the instabilities at work and wavelet analysis techniques are used to characterize the regime of energy conversions (from electromagnetic to electrostatic structures, from large to small length scales). This study elucidates a possible scenario to account for the particle acceleration and the wave dissipation in inhomogeneous plasmas. It would consist of successive phases of acceleration along the magnetic field, the development of an electrostatic turbulence, the thermalization and the heating of the plasma. Space plasma physics (charged particle motion and acceleration; numerical studies).

scholarly journals Dissipation of the striped pulsar wind and non-thermal particle acceleration: 3D PIC simulations

2020 ◽  
Vol 642 ◽  
pp. A204
Author(s):  
Benoît Cerutti ◽  
Alexander A. Philippov ◽  
Guillaume Dubus
Keyword(s):  
Particle Acceleration ◽  
Current Sheet ◽  
Large Scale ◽  
Magnetic Energy ◽  
Rotation Axis ◽  
Moving Frame ◽  
Particle Spectrum ◽  
Secondary Current ◽  
Flux Ropes ◽  
Pulsar Wind

Context. The formation of a large-scale current sheet is a generic feature of pulsar magnetospheres. If the magnetic axis is misaligned with the star rotation axis, the current sheet is an oscillatory structure filling an equatorial wedge determined by the inclination angle, known as the striped wind. Relativistic reconnection could lead to significant dissipation of magnetic energy and particle acceleration, although the efficiency of this process is debated in this context. Aims. In this study, we aim at reconciling global models of pulsar wind dynamics and reconnection in the stripes within the same numerical framework in order to shed new light on dissipation and particle acceleration in pulsar winds. Methods. To this end, we perform large three-dimensional particle-in-cell simulations of a split-monopole magnetosphere, from the stellar surface up to 50 light-cylinder radii away from the pulsar. Results. Plasmoid-dominated reconnection efficiently fragments the current sheet into a dynamical network of interacting flux ropes separated by secondary current sheets that consume the field efficiently at all radii, even past the fast magnetosonic point. Our results suggest there is a universal dissipation radius solely determined by the reconnection rate in the sheet, lying well upstream from the termination shock radius in isolated pair-producing pulsars. The wind bulk Lorentz factor is much less relativistic than previously thought. In the co-moving frame, the wind is composed of hot pairs trapped within flux ropes with a hard broad power-law spectrum, whose maximum energy is limited by the magnetization of the wind at launch. Conclusions. We conclude that the striped wind is most likely fully dissipated when it enters the pulsar wind nebula. The predicted wind particle spectrum after dissipation is reminiscent of the Crab Nebula radio-emitting electrons.

scholarly journals PIC Simulations of Excited Waves in the Plasmoid Instability

2022 ◽  
Vol 8 ◽  
Author(s):  
Mahdi Shahraki Pour ◽  
Mahboub Hosseinpour
Keyword(s):  
Particle Acceleration ◽  
Kinetic Energy ◽  
Solar Corona ◽  
Current Sheet ◽  
Electromagnetic Waves ◽  
Magnetic Energy ◽  
Particle In Cell ◽  
Guide Field ◽  
Collisionless Regime ◽  
Accelerated Particles

Fragmentation of an elongated current sheet into many reconnection X-points, and therefore multiple plasmoids, occurs frequently in the solar corona. This speeds up the release of solar magnetic energy in the form of thermal and kinetic energy. Moreover, due to the presence of multiple reconnection X-points, the particle acceleration is more efficient in terms of the number of accelerated particles. This type of instability called “plasmoid instability” is accompanied with the excitation of some electrostatic/electromagnetic waves. We carried out 2D particle-in-cell simulations of this instability in the collisionless regime, with the presence of non-uniform magnetic guide field to investigate the nature of excited waves. It is shown that the nature and properties of waves excited inside and outside the current sheet are different. While the outside perturbations are transient, the inside ones are long-lived, and are directly affected by the plasmoid instability process.

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