  High resolution spectroscopy of AE Aquarii with the XMM-Newton RGS has
enabled us to measure the electron number density of the X-ray-emitting hot
plasma to be ~1E11/cm**-3 by means of intensity ratios of the He-like triplet
of Nitrogen and Oxygen. Incorporating with the emission measure evaluated by
the EPIC cameras, we have also found a linear scale of the plasma to be ~5E10
cm. Both these values, obtained model-independently, are incompatible with a
standard post-shock accretion column of a magnetized white dwarf, but are
naturally interpreted as the plasma being formed through interaction between an
accretion flow and the magnetosphere of the white dwarf. Our results provide
another piece of evidence of the magnetic propeller effect being at work in AE
Aqr.
