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

Abstract

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 (M_(BH)/M_⊙) = 9.08 ± 0.18. The X-ray spectrum of this source can be well described by a power law of photon index Γ = 1.82 ± 0.05 with E_(cut) = 152^(+103)_(−54) 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 kT_e = 56 ± 3 keV for 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 × 10^(45) erg s^(−1)). The quasar is X-ray loud, with an unusually flat observed optical-to-X-ray spectral slope α_(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.

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