The first XMM-Newton spectrum of a high redshift quasar - PKS 0537-286

We present XMM-Newtonobservations of the high redshift ($z=3.104$), radio-loud quasar PKS 0537-286. The EPIC CCD cameras provide the highest signal-to-noise spectrum of a high-zquasar to date. The EPIC observations show that PKS 0537-286 is extremely X-ray luminous ($L_{\rm X}=2$1047erg s-1), with an unusually hard X-ray spectrum ($\Gamma=1.27\pm0.02$). The flat power-law emission extends over the whole observed energy range (0.4 to 40 keV in the quasar rest frame); there is no evidence of intrinsic absorption, which has been claimed in PKS 0537-286 and other high zquasars. However, there is evidence for weak Compton reflection. A redshiftediron K line, observed at 1.5 keV - corresponding to ~6.15 keV in the quasar rest frame - is detected at 95% confidence. If confirmed, this is the most distant iron K line known. The line equivalent width is small (33 eV), consistent with the "X-ray Baldwin effect" observed in other luminous quasars. The reflected continuum is also weak ($R \la$0.25). We find the overall spectral energy distribution of PKS 0537-286 is dominated by the X-ray emission, which, together with the flat power-law and weak reflection features, suggests that the X-radiation from PKS 0537-286 is dominated by inverse Compton emission associated with a face-on relativistic jet.