Electron-ion coupling upstream of relativistic collisionless shocks

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Abstract

We argue and demonstrate by particle-in-cell simulations that the synchrotron maser instability could develop at the front of a relativistic, magnetized shock. The instability generates strong low-frequency electromagnetic waves propagating both upstream and downstream of the shock. Upstream of the shock, these waves make electrons lag behind ions so that a longitudinal electric field arises and the electrons are accelerated up to the ion kinetic energy. Then thermalization at the shock front results in a plasma with equal temperatures of electrons and ions. Downstream of the shock, the amplitude of the maser-generated wave may exceed the strength of the shock-compressed back-ground magnetic field. In this case the shock-accelerated particles radiate via nonlinear Compton scattering rather than via a synchrotron mechanism. The spectrum of the radiation differs, in the low-frequency band, from that of the synchrotron radiation, providing possible observational tests of the model.

Original languageEnglish
Pages (from-to)1297-1305
Number of pages9
JournalAstrophysical Journal
Volume652
Issue number2 I
DOIs
StatePublished - 1 Dec 2006

Keywords

  • Instabilities
  • Magnetic fields
  • Masers
  • Radiation mechanisms: nonthermal shock waves

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