2003A&A...408..119P

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 2keV). We find that Q0056-363 is a powerful X-ray quasar, with a 0.3-12keV unabsorbed luminosity of about 1.2x10⁴⁵erg/s with the largest part (∼67%) emitted below 2keV. The spectrum reveals a large featureless soft X-ray excess below 2keV and a strong broad FeK_α line at 6.4keV (in the quasar frame). The FeK_α line is due to low to moderate ionization states of iron (i.e., <FeXVII), with an equivalent width of about 250eV and a velocity width of about 25000km/s. Q0056-363 is presently the most luminous AGN known to exhibit such a broad and intense FeK_α 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 0.3-12keV and the FeK_α 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 5x10⁸M_☉.