Slow temperature equilibration behind the shock front of SN 1006

We report on the observation of O VII Doppler line broadening in a compact knot at the edge of SN 1006 detected with the Reflective Grating Spectrometer on board XMM-Newton. The observed line width of σ = 3.4± 0.5 eV at a line energy of 574 eV indicates an oxygen temperature of kT = 528± 150 keV. Combined with the observed electron temperature of ∼ 1.5 keV the observed broadening is direct evidence for temperature nonequilibration in high Mach number shocks, and slow subsequent equilibration. The O VII line emission allows an accurate determination of the ionization state of the plasma, which is characterized by a relatively high forbidden line contribution, indicating log(net) ≃ 9.2. Subject headings: shock waves – X-rays: observations individual (SN 1006) – supernova remnants