Microphysics of electron acceleration and heating at nonrelativistic perpendicular shocks of young supernova remnants
2019 July 22
Particle injection is one of the most troublesome and still unresolved issues of the theory of diffusive shock acceleration (DSA) of galactic cosmic rays. Supernova remnants harbor non-relativistic collisionless shocks with high Alfven and sonic Mach numbers. To accelerate electrons up to the injection energy, a shock-internal acceleration mechanism is required. We present results of two-dimensional fully kinetic particle-in-cell simulations of perpendicular shocks with different values of Mach numbers and ion-to-electron mass ratios. Such systems are known as supercritical shocks, in which the shock potential is capable to reflect portion of upcoming ions upstream. In weakly magnetized plasmas that leads to the excitation of the electrostatic Buneman instability in the shock foot and to the formation of magnetic filaments in the shock ramp, resulting from the ion-beam-Weibel instability. These instabilities are responsible for electron acceleration via shock surfing acceleration and magnetic reconnection. The individual impact of these acceleration processes on the production of non-thermal electrons is discussed here. They strongly depend on the Mach number and ion-to-electron mass ratio, which is critical for predicting the electron injection efficiency at shocks with realistic physical parameters. The redistribution of ion bulk kinetic energy into ion thermal, electron thermal and magnetic field energies in the shock transition are also considered here.