부산대학교 도서관

We present results from a 20 ks XMM–Newton director's discretionary time observation of the radio-loud quasar CFHQS J142952 + 544717 at z  = 6.18, whose extreme X-ray luminosity was recently revealed by the SRG / eROSITA telescope in the course of its first all-sky survey. The quasar has been confidently detected with a total of ∼1400 net counts in the 0.2–10 keV energy band (1.4–72 keV in the object's rest frame). Its measured spectrum is unusually soft and can be described by an absorbed power-law model with a photon index of Γ = 2.5 ± 0.2. There are no signs of a high-energy cut-off or reflected component, with a 90 per cent upper limit on the fluorescence iron K α equivalent width of ≈290 eV and the corresponding upper limit on the iron K-edge absorption depth of 0.6. We have detected, at the >95 per cent confidence level, an excess absorption above the Galactic value, corresponding to a column density N H = 3 ± 2 × 1022 cm−2 of material located at z  = 6.18. The intrinsic luminosity of CFHQS J142952 + 544717 in the 1.4–72 keV energy band is found to be |$5.5_{-0.6}^{+0.8} \times 10^{46}$|  erg s−1. We did not detect statistically significant flux changes between two SRG scans and the XMM–Newton observation, spanning over ∼7.5 months, implying that the quasar remained at this extremely high-luminosity level for at least a month in its rest frame. We put forward the hypothesis that the extreme X-ray properties of CFHQS J142952 + 544717 are associated with inverse Compton scattering of cosmic microwave background photons (at z  = 6.18) in its relativistic jets. [ABSTRACT FROM AUTHOR]