  It is argued and demonstrated 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 background 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.
