Heating and Nonthermal Particle Acceleration in Relativistic, Transverse Magnetosonic Shock Waves in Proton‐Electron‐Positron Plasmas

We report the results of 1D particle-in-cell simulations of ultrarelativisticshock waves in proton-electron-positron plasmas. We consider magnetized shockwaves, in which the upstream medium carries a large scale magnetic field,directed transverse to the flow. Relativistic cyclotron instability of eachspecies as the incoming particles encounter the increasing magnetic fieldwithin the shock front provides the basic plasma heating mechanism. The mostsignificant new results come from simulations with mass ratio $m_p/m_\pm =100$. We show that if the protons provide a sufficiently large fraction of theupstream flow energy density (including particle kinetic energy and Poyntingflux), a substantial fraction of the shock heating goes into the formation ofsuprathermal power-law spectra of pairs. Cyclotron absorption by the pairs ofthe high harmonic ion cyclotron waves, emitted by the protons, provides thenon-thermal acceleration mechanism. As the proton fraction increases, thenon-thermal efficiency increases and the pairs' power-law spectra harden. We suggest that the varying power law spectra observed in synchrotron sourcespowered by magnetized winds and jets might reflect the correlation of theproton to pair content enforced by the underlying electrodynamics of thesesources' outflows, and that the observed correlation between the X-ray spectraof rotation powered pulsars with the X-ray spectra of their nebulae mightreflect the same correlation.Comment: 32 pages, 13 figures, accepted for publication in Ap