An intense and broad Fe K (alpha) line observed in the X-ray luminous quasar Q 0056-363 with XMM-Newton

We present an XMM-Newton observation of the radio-quiet quasar Q0056-363 ( z=0.162). This is the first time that this quasar is observed in the hard X-ray range (above 2 keV). We find that Q0056-363 is a powerful X-ray quasar, with a 0.3-12 keV unabsorbed luminosity of about 1.2*10^45 erg s^-1 with the largest part (~67%) emitted below 2 keV. The spectrum reveals a large featureless soft X-ray excess below 2 keV and a strong broad Fe K (alpha) line at 6.4 keV (in the quasar frame). The Fe K (alpha) line is due to low to moderate ionization states of iron (i.e., < Fe XVII), with an equivalent width of about 250 eV and a velocity width of about 25 000 km s^-1. Q0056-363 is presently the most luminous AGN known to exhibit such a broad and intense Fe K (alpha) line profile from near neutral iron. The line can be fitted with a relativistic profile from an accretion disc around either a Schwarzschild (non-rotating) or a Kerr (rotating) black hole. A combination of two thermal Comptonization components and a disc reflection model is favored to explain both the continuum over the energy range 0.3-12 keV and the Fe K (alpha) line. A patchy corona covering a large part of the inner disc surface is needed in order to be compatible with the accretion rate inferred from the spectral energy distribution of Q0056-363, unless the mass of the black hole is much higher than about 5*10^8 M(circled dot operator).