Scientific Results

Perpendicular relativistic shocks in magnetized pair plasma

Year: 2018

Authors: Plotnikov I., Grassi A., Grech M.

Autors Affiliation: CNR, INO, I-56127 Pisa, Italy.

Abstract: Perpendicular relativistic (gamma(0)=10) shocks in magnetized pair plasmas are investigated using two-dimensional Particle-in-Cell simulations. A systematic survey, from unmagnetized to strongly magnetized shocks, is presented accurately capturing the transition from Weibel-mediated to magnetic-reflection-shaped shocks. This transition is found to occur for upstream flow magnetizations 10(-3) < sigma < 10(-2) at which a strong perpendicular net current is observed in the precursor, driving the so-called current-filamentation instability. The global structure of the shock and shock formation time are discussed. The magnetohydrodynamics shock jump conditions are found in good agreement with the numerical results, except for 10(-4) < sigma < 10(-2) where a deviation up to 10 per cent is observed. The particle precursor length converges towards the Larmor radius of particles injected in the upstream magnetic field at intermediate magnetizations. For sigma > 10(-2), it leaves place to a purely electromagnetic precursor following from the strong emission of electromagnetic waves at the shock front. Particle acceleration is found to be efficient in weakly magnetized perpendicular shocks in agreement with previous works, and is fully suppressed for sigma > 10(-2). Diffusive shock acceleration is observed only in weakly magnetized shocks, while a dominant contribution of shock drift acceleration is evidenced at intermediate magnetizations. The spatial diffusion coefficients are extracted from the simulations allowing for a deeper insight into the self-consistent particle kinematics and scale with the square of the particle energy in weakly magnetized shocks. These results have implications for particle acceleration in the internal shocks of active galactic nucleus jets and in the termination shocks of pulsar wind nebulae.


Volume: 477 (4)      Pages from: 5238  to: 5260

KeyWords: acceleration of particles; plasmas; relativistic processes; shock waves;
DOI: 10.1093/mnras/sty979

Citations: 9
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