2022ApJ...924L..25Y

We report X-ray observations of the most distant known gravitationally lensed quasar, J0439+1634 at z = 6.52, which is also a broad absorption line (BAL) quasar, using the XMM-Newton Observatory. With a 130 ks exposure, the quasar is significantly detected as a point source at the optical position with a total of 358_–19⁺¹⁹ net counts using the EPIC instrument. By fitting a power law plus Galactic absorption model to the observed spectra, we obtain a spectral slope of Γ=1.45_–0.09^+0.10. The derived optical-to-X-ray spectral slope α_ox is -2.07_–0.01^+0.01, suggesting that the X-ray emission of J0439+1634 is weaker by a factor of 18 than the expectation based on its 2500 Å luminosity and the average α_ox versus luminosity relationship. This is the first time that an X-ray weak BAL quasar at z > 6 has been observed spectroscopically. Its X-ray weakness is consistent with the properties of BAL quasars at lower redshift. By fitting a model including an intrinsic absorption component, we obtain intrinsic column densities of N_H=2.8_–0.6^+0.7×10²³cm^–2 and N_H=4.3_–1.5^+1.8×10²³cm^–2, assuming a fixed Γ of 1.9 and a free Γ, respectively. The intrinsic rest-frame 2-10 keV luminosity is derived as (9.4-15.1) x 10⁴³ erg s^–1, after correcting for lensing magnification (µ = 51.3). The absorbed power-law model fitting indicates that J0439+1634 is the highest redshift obscured quasar with a direct measurement of the absorbing column density. The intrinsic high column density absorption can reduce the X-ray luminosity by a factor of 3-7, which also indicates that this quasar could be a candidate intrinsically X-ray weak quasar.