X-ray properties of the quasar HE0450-2958

We present an {\it XMM-Newton} EPIC observation of HE0450-2958 which may be a ``naked''quasar as suggested by Magain et al. The \xmm EPIC spectra show a substantial soft X-ray excess, a steep photon index, as well as marginal evidence for a weak Fe K$\alpha$ line. The X-ray absorption is consistent with the galactic level. The 0.3-10 keV EPIC spectra can be fitted by a power law plus a blackbody model, however, the fit by the relativistically blurred photoionized disc reflection is better. We estimate the black hole mass of $2^{+7}_{-1.3} \times 10^{7} M_{\odot}$ from the X-ray variability. This broadly agrees with the value derived from the optical \hb line width. These results support a high-state Seyfert galaxy of the source. HE0450-2958 shares similar properties of transitionary objects from ultra-luminous infrared galaxies to quasars. We suggest that HE0450-2958 is just in the beginning of an optical quasar window.