Perpendicular relativistic shocks in magnetized pair plasma

Year: 2018

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

Autors Affiliation: Univ Toulouse, CNRS, Inst Rech Astrophys & Planetol, 9 Ave Colonel Roche,BP 44346, F-31028 Toulouse, France; Princeton Univ, Dept Astrophys Sci, Peyton Hall, Princeton, NJ 08544 USA; Univ Paris Saclay, UPMC Univ Paris 06, CEA, CNRS,Ecole Polytech,LULI, F-75252 Paris 05, France; Univ Pisa, Dipartimento Fis Enr Fermi, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy; CNR, INO, I-56127 Pisa, Italy; UPMC Univ Paris 06, Univ Paris Saclay, CEA, CNRS,Ecole Polytech,LULI, F-91128 Palaiseau, France.

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.

Journal/Review: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

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

More Information: The authors acknowledge fruitful discussions with Martin Lemoine, Guy Pelletier, Benoit Cerutti, Lorenzo Sironi, and Anatoly Spitkovsky as well as Laurent Gremillet and Mark Dieckmann for insightful remarks on PIC codes. The authors also thank the SMILEI development team for technical support. Financial support from Grant No. ANR-11-IDEX-0004-02 Plas@Par is acknowledged. AG also acknowledges support from the Universite Franco-Italienne through the Vinci program (Grant No. C2-133). This work was granted access to the HPC resources of CALMIP supercomputing centre at Universite de Toulouse under the allocation 2016-p1504, and from GENCI-TGCC (Grant No. 2017-x2016057678).
KeyWords: acceleration of particles; plasmas; relativistic processes; shock waves
DOI: 10.1093/mnras/sty979

Citations: 38
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