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

TL;DR

This study analyzes X-ray and optical data of the radio-quiet quasar QSO B2202-209, revising its redshift and black hole mass, and characterizing its coronal properties, revealing similarities to local AGN despite its high luminosity.

Contribution

It provides the first detailed coronal property measurements of QSO B2202-209, including revised redshift, black hole mass, and coronal temperature estimates, and discusses implications of its optical-to-X-ray properties.

Findings

Coronal temperature estimated at 42-56 keV depending on geometry.

Revised redshift to z=0.532 and black hole mass of ~10^9.08 solar masses.

The quasar exhibits an unusually flat optical-to-X-ray spectral slope.

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, $\log (M_{\rm BH}/M_{\odot}) = 9.08 \pm 0.18$. The X-ray spectrum of this source can be well described by a power-law of photon index $\Gamma = 1.82 \pm 0.05$ with $E_{\rm cut} = 152_{-54}^{+103}\,{\rm keV}$, in the rest frame of the source. Assuming a Comptonisation model, we estimate the coronal temperature to be $kT_{\rm e}=42\pm 3 \,{\rm keV}$ and $kT_{\rm e}= 56 \pm 3\,{\rm keV}$ for a spherical and a slab geometry, respectively. The coronal properties are comparable to the ones derived for local AGN, despite a difference of around one order of magnitude in black hole mass and X-ray luminosity ($L_{2-10} = 1.93\times 10^{45}\,{\rm erg\,s^{-1}}$). The quasar is X-ray loud, with an unusually flat observed optical-to-X-ray spectral slope $\alpha_{\rm OX} = 1.00 \pm 0.02$, 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 disk, leading to a reduction in the observed UV continuum light.