  We report on the XMM-Newton observation of the HMXRB X Persei, the prototype
of the persistent and low-luminosity Be/neutron star pulsars, which was
performed on February 2003. The source was detected at a luminosity level of ~
1.4x10^35 erg/s, which is the highest level of the latest three decades. The
pulsation period has increased up to 839.3 s, thus confirming the overall
spin-down of the NS detected in the previous observations. The folded
light-curve has a complex structure, with features not observed at lower
luminosities, and shows a significant energy dependence. The spectral analysis
reveals the presence of a significant excess at low energies over the main
power-law spectral component, which can be described by a black-body spectrum
of high temperature (kT_BB ~ 1.5 keV) and small emitting region (R_BB ~ 340 m);
its properties are consistent with a polar-cap origin. Phase-resolved
spectroscopy shows that the emission spectrum varies along the pulse period,
but it is not possible to prove whether the thermal component is pulsed or not.
