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Accepted · first revision · record

Title: Electron heating and electron-ion temperature ratio at shocks
Plain: Behind fast shocks in supernova remnants, electrons end up much colder than ions, while behind slow shocks the two are similar. Which processes heat electrons inside a collisionless shock is not known.
Precise: Balmer-line observations of supernova remnant shocks show downstream $T_{\mathrm{e}}/T_{\mathrm{i}}$ near 1 at low shock speed and well below 1 at high speed. Identify the electron heating mechanism (cross-shock potential, wave heating by Buneman or whistler instabilities, reconnection in the shock transition) and derive $T_{\mathrm{e}}/T_{\mathrm{i}}$ versus Mach number and obliquity. An answer is a derived relation matching observations and kinetic simulations.
Settled by: Kinetic simulations at realistic mass ratio reproducing the observed $T_{\mathrm{e}}/T_{\mathrm{i}}$ trend, with the mechanism identified.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)