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

¹ X-Ray Astronomy Group, Department of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK
² Max-Planck-Institut für extraterrestrische Physik, Postfach 1603, 85748 Garching, Germany
³ Institut für Astronomie und Astrophysik - Astronomie, University of Tübingen, Waldhäuser Strasse 64, 72076 Tübingen, Germany
⁴ IFC Milan, 20133 Milano, Italy

Corresponding author: J. N. Reeves, jnr@star.le.ac.uk

Received: 2 October 2000
Accepted: 17 October 2000

Abstract

We present XMM-Newton observations of the high redshift (), radio-loud quasar PKS 0537-286. The EPIC CCD cameras provide the highest signal-to-noise spectrum of a high-z quasar to date. The EPIC observations show that PKS 0537-286 is extremely X-ray luminous ( 10⁴⁷ erg s^-1), with an unusually hard X-ray spectrum (). 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 z quasars. However, there is evidence for weak Compton reflection. A redshifted iron 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 (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.