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 \sigma = 3.4 \pm 0.5 eV at a line energy of 574 eV indicates an oxygen temperature of kT = 528 \pm 150 keV .
Combined with the observed electron temperature of \sim 1.5 keV the observed broadening is direct evidence for temperature non-equilibration 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 ( n _ { e } t ) \simeq 9.2 .