Electron heating at quasi-perpendicular collisionless shocks

Adiabatic and non-adiabatic electron dynamics have been proposed to explain electron heating across collisionless shocks. We analyze the evolution of the suprathermal electrons across 310 quasi-perpendicular shocks with $1.7<M_A<48$ using in-situ measurements. We show that the electron heating mechanism shifts from predominantly adiabatic to non-adiabatic for the Alfvénic Mach number in the de Hoffman-Teller $\gtrsim 30$ with the latter constituting 48% of the analyzed shocks. The observed non-adiabatic heating is consistent with the stochastic shock drift acceleration mechanism.