2020ApJ...900..189C

We present deep Chandra observations of PSO J231.6576-20.8335, a quasar at redshift z = 6.59 with a nearby (∼8 proper kpc) companion galaxy. The Atacama Large Millimeter/submillimeter Array observed both the quasar and companion to be bright in [C II], and the system has significant extended Lyα emission around the quasar, suggesting that a galaxy merger is ongoing. Unlike previous studies of two similar systems, and despite observing the system with Chandra for 140 ks, we do not detect the companion in X-rays. The quasar itself is detected, but only 13.3_–3.7^+4.8 net counts are observed. From a basic spectral analysis, the X-ray spectrum of the quasar is soft (hardness ratio of H R =-0.60_–0.27^+0.17, power-law index of Γ=2.6_–0.9^+1.0), which results in a rest-frame X-ray luminosity comparable to other bright quasars (L_2–10=1.09_–0.70^+2.20×10⁴⁵ erg s^–1) despite the faint observed X-ray flux. We highlight two possible interpretations of this result: the quasar has a steep value of Γ-potentially related to observed ongoing Eddington accretion-thereby pushing much of the emission out of our observed band, or the quasar has a more normal spectrum (Γ ∼ 2) but is therefore less X-ray luminous (L_2–10∼0.6×10⁴⁵ erg s^–1).