  The central star of NGC 2392 shows the hardest X-ray emission among central
stars of planetary nebulae (CSPNe). The recent discovery of a spectroscopic
companion with an orbital period of 1.9 days could provide an explanation for
its hard X-ray emission, as well as for the collimation of its fast outflow.
Here we analyse the available Chandra and XMM-Newton X-ray observations to
determine accurately the spectral and temporal variation properties of the CSPN
of NGC 2392. The X-ray emission can be described by an absorbed thermal plasma
model with temperature 26$^{+8}_{-5}$ MK and X-ray luminosity
(8.7$\pm$1.0)$\times$10$^{30}$ erg s$^{-1}$. No long-term variability is
detected in the X-ray emission level, but the Chandra light curve is suggestive
of short-term variations with a period $\sim$0.26 days. The possible origins of
this X-ray emission are discussed. X-ray emission from the coronal activity of
a companion or shocks in the stellar wind can be ruled out. Accretion of
material from an unseen main-sequence companion onto the CSPN or from the CSPN
wind onto a white dwarf companion are the most plausible origins for its hard
X-ray emission, although the mismatch between the rotational period of the CSPN
and the modulation time-scale of the X-ray emission seems to preclude the
former possibility.
