087091

High luminosity quasars are unique laboratories to test our understanding of X-ray coronae in AGN. We propose joint XMM-Newton and NuSTAR observations of a luminous comma optically-selected comma non-jetted quasar at z=0.821. Our main goal is to measure the high-energy cutoff in its X-ray spectrum comma hence constraining comma in the framework of Comptonization models comma its coronal temperature and optical depth. This will allow us to test whether the same physical conditions hold in quasars at luminosities and masses 100 times higher than those probed in so far in the nearby Universe comma exploring the unknown X-ray properties of the quasar population at intermediate redshifts openParz = 0.1-1closePar comma constituting half the age of the Universe.