Electron heating in astrophysical blast waves

Gamma-ray bursts, blazars, and supernovae provide ideal environments for efficient energy channeling between different plasma species through collective processes. Astrophysical shock waves are one of the most outstanding representatives of such complex many-body phenomena. Extensively studied in astrophysical and laboratory environments, observations and kinetic simulations indicate strong electron heating in the precursor of collisionless shock waves propagating in unmagnetized electron-ion plasmas. We outline a theoretical model accounting for the electron heating via a Joule-like process through the interplay between pitch-angle scattering in the microturbulence and the coherent electrostatic field induced by the difference in inertia between species. Using analytical kinetic estimates, semi-analytical Monte Carlo methods, and ab-initio Particle-In-Cell simulations, we first demonstrate the validity of this model in the relativistic regime relevant for the afterglow emission of gamma-ray burst [1] and then extend it to characterize the electron to ion temperature ratio in the downstream of nonrelativistic high-Mach numbers shock waves relevant for supernova remnants and laboratory experiments.

[1] A. Vanthieghem et al., ApJ Letters 930 L8 (2022)