Coronal properties of the luminous radio-quiet quasar QSO B2202-209

We present an analysis of the joint XMM-Newton and NuSTAR observations of the radio-quiet quasar QSO B2202-209. Using an optical observation from the Hale Telescope at the Palomar Observatory, we revise the redshift of the source from the previously reported z = 1.77 to z = 0.532, and we estimate the mass of the central black hole, log (MBH/M-circle dot) = 9.08 +/- 0.18. The X-ray spectrum of this source can be well described by a power law of photon index Gamma = 1.82 +/- 0.05 with E-cut = 152(-54)(+103) keV, in the rest frame of the source. Assuming a Comptonization model, we estimate the coronal temperature to be kT(e) = 42 +/- 3 keV and kTe = 56 +/- 3 keVfor a spherical and a slab geometry, respectively. The coronal properties are comparable to the ones derived for local active galactic nuclei, despite a difference of around one order of magnitude in black hole mass and X-ray luminosity ( L-2 (-) (10) = 1.93 x 10(45) erg s(-1)). The quasar is X-ray loud, with an unusually flat observed optical-to-X-ray spectral slope alpha(OX) = 1.00 +/- 0.02, and has an exceptionally strong optical [O-III] line. Assuming that both the X-ray emission and the [O-III] line are isotropic, these two extreme properties can be explained by a nearly edge-on disc, leading to a reduction in the observed ultraviolet continuum light.