Particle acceleration in neutron star ultra-strong electromagnetic fields

Tomczak, Ivan; Pétri, Jérôme

doi:10.1017/s0022377820000835

Cited by 6 publications

(3 citation statements)

References 26 publications

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“…We emphasize, however, that, for realistic neutron star applications, accuracy for large strength parameters is compulsory and therefore going beyond ‘double precision’ must not be discarded. But in depth analysis of this requirement is left to another work as described by a companion paper (Tomczak & Pétri 2020) specifically dealing with particle acceleration in ultra-strong electromagnetic fields of neutron stars.…”

Section: Numerical Tests In Spatially and Temporally Varying Fieldsmentioning

confidence: 99%

A relativistic particle pusher for ultra-strong electromagnetic fields

Pétri

2020

J. Plasma Phys.

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Kinetic plasma simulations are nowadays commonly used to study a wealth of nonlinear behaviours and properties in laboratory and space plasmas. In particular, in high-energy physics and astrophysics, the plasma usually evolves in ultra-strong electromagnetic fields produced by intense laser beams for the former or by rotating compact objects such as neutron stars and black holes for the latter. In these ultra-strong electromagnetic fields, the gyro-period is several orders of magnitude smaller than the time scale on which we desire to investigate the plasma evolution. Some approximations are required such as, for instance, artificially decreasing the electromagnetic field strength, which is certainly not satisfactory. The main flaw of this downscaling is that it cannot reproduce particle acceleration to ultra-relativistic speeds with a Lorentz factor above $\gamma \approx 10^3$ – $10^4$ . In this paper, we design a new algorithm able to catch particle motion and acceleration to a Lorentz factor of up to $10^{15}$ or even higher by using Lorentz boosts to special frames where the electric and magnetic field are parallel. Assuming that these fields are locally uniform in space and constant in time, we solve analytically the equation of motion in a tiny region smaller than the length scale of the spatial and temporal gradient of the field. This analytical integration of the orbit severely reduces the constraint on the time step, allowing us to use large time steps, avoiding resolving the ultra-high gyro-frequency. We performed simulations in ultra-strong spatially and time-dependent electromagnetic fields, showing that our particle pusher is able to follow accurately the exact analytical solution for very long times. This property is crucial to properly capture for instance lepton electrodynamics in electromagnetic waves produced by fast rotating neutron stars. We conclude with a simple implementation of our new pusher into a one-dimensional relativistic electromagnetic particle-in-cell code, testing it against plasma oscillations, two-stream instabilities and strongly magnetized relativistic shocks.

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Section: Numerical Tests In Spatially and Temporally Varying Fieldsmentioning

confidence: 99%

A relativistic particle pusher for ultra-strong electromagnetic fields

Pétri

2020

J. Plasma Phys.

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“…Recently Pétri (2020) developed an algorithm to evolve particles in a strong electromagnetic field. Tomczak & Pétri (2020) applied it to a magnetic dipole associated with strongly magnetised rotating neutron stars. Gordon et al (2017b) and Gordon et al (2017a) showed how to implement a fully covariant particle pusher and gave some hints that the radiation reaction should be included.…”

Section: Introductionmentioning

confidence: 99%

Particle acceleration and radiation reaction in a strongly magnetised rotating dipole

Pétri

2022

A&A

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Context. Neutron stars are surrounded by ultra-relativistic particles efficiently accelerated by ultra strong electromagnetic fields. These particles copiously emit high energy photons through curvature, synchrotron and inverse Compton radiation. However so far, no numerical simulations were able to handle such extreme regimes of very high Lorentz factors and magnetic field strengths close or even above the quantum critical limit of 4,4 • 10 9 T. Aims. It is the purpose of this paper to study particle acceleration and radiation reaction damping in a rotating magnetic dipole with realistic field strengths of 10 5 T to 10 10 T typical of millisecond and young pulsars as well as of magnetars. Methods. To this end, we implemented an exact analytical particle pusher including radiation reaction in the reduced Landau-Lifshitz approximation where the electromagnetic field is assumed constant in time and uniform in space during one time step integration. The position update is performed using a velocity Verlet method. We extensively tested our algorithm against time independent background electromagnetic fields like the electric drift in cross electric and magnetic fields and the magnetic drift and mirror motion in a dipole. Eventually, we apply it to realistic neutron star environments. Results. We investigated particle acceleration and the impact of radiation reaction for electrons, protons and iron nuclei plunged around millisecond pulsars, young pulsars and magnetars, comparing it to situations without radiation reaction. We found that the maximum Lorentz factor depends on the particle species but only weakly on the neutron star type. Electrons reach energies up to γ e ≈ 10 8 − 10 9 whereas protons energies up to γ p ≈ 10 5 − 10 6 and iron up to γ ≈ 10 4 − 10 5 . While protons and irons are not affected by radiation reaction, electrons are drastically decelerated, reducing their maximum Lorentz factor by 2 orders of magnitude. We also found that the radiation reaction limit trajectories fairly agree with the reduced Landau-Lifshitz approximation in almost all cases.

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“…Finding accurate and exact analytical solutions to the particle equation of motion is crucial in ultra-strong electromagnetic fields as shown by Pétri (2020b) in the Lorentz force limit. Some applications to neutron stars have been explored by Tomczak & Pétri (2020). Different approaches exist to tackle the problem of finding exact and efficient implementations of the Lorentz force equation, see for instance Gordon et al (2017) and Gordon & Hafizi (2021) who also discuss the possibility to add radiation reaction.…”

Section: Introductionmentioning

confidence: 99%

Particle acceleration and radiation reaction in strong spherical electromagnetic waves

Pétri

2021

Preprint

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Strongly magnetized and fast rotating neutron stars are known to be efficient particle accelerators within their magnetosphere and wind. They are suspected to accelerate leptons, protons and maybe ions to extreme relativistic regimes where the radiation reaction significantly feeds back to their motion. In the vicinity of neutron stars, magnetic field strengths are close to the critical value of B c ∼ 4,4 • 10 9 T and particle Lorentz factors of the order γ ∼ 10 9 are expected. In this paper, we investigate the acceleration and radiation reaction feedback in the pulsar wind zone where a large amplitude low frequency electromagnetic wave is launched starting from the light-cylinder. We design a semianalytical code solving exactly the particle equation of motion including radiation reaction in the Landau-Lifshits approximation for a null-like electromagnetic wave of arbitrary strength parameter and elliptical polarization. Under conventional pulsar conditions, asymptotic Lorentz factor as high as 10 8 − 10 9 are reached at large distances from the neutron star. However, we demonstrate that in the wind zone, within the spherical wave approximation, radiation reaction feedback remains negligible.

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Particle acceleration in neutron star ultra-strong electromagnetic fields

Cited by 6 publications

References 26 publications

A relativistic particle pusher for ultra-strong electromagnetic fields

A relativistic particle pusher for ultra-strong electromagnetic fields

Particle acceleration and radiation reaction in a strongly magnetised rotating dipole

Particle acceleration and radiation reaction in strong spherical electromagnetic waves

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