Collisionless ion-electron energy exchange in magnetized shocks.

Energy partition between ions and electrons in collisionless shocks has been a long-standing unsolved fundamental physical question. We show that kinetic simulations of moderate Alfvénic Mach number, magnetized, collisionless shocks reveal rapid, faster-than-Coulomb, energy exchange between ions and electrons when the plasma is sufficiently magnetized. Using kinetic and multifluid models with counter-streaming ions, we identify resonances between electron whistler and ion magnetohydrodynamic waves that account for this rapid energy exchange.