2021ApJ...922L..24C

The z = 6.327 quasar SDSS J010013.02+280225.8 (hereafter J0100+2802) is believed to be powered by a black hole more massive than 10¹⁰ M_☉, making it the most massive black hole known in the first billion years of the universe. However, recent high-resolution ALMA imaging shows four structures at the location of this quasar, potentially implying that it is lensed with a magnification of µ ∼ 450 and thus its black hole is significantly less massive. Furthermore, for the underlying distribution of magnifications of z >= 6 quasars to produce such an extreme value, theoretical models predict that a larger number of quasars in this epoch should be lensed, implying further overestimates of early black hole masses. To provide an independent constraint on the possibility that J0100+2802 is lensed, we reanalyzed archival XMM-Newton observations of the quasar and compared the expected ratios of X-ray luminosity to rest-frame UV and IR luminosities. For both cases, J0100+2802's X-ray flux is consistent with the no-lensing scenario; while this could be explained by J0100+2802 being X-ray faint, we find it does not have the X-ray or optical spectral features expected for an X-ray faint quasar. Finally, we compare the overall distribution of X-ray fluxes for known, typical z >= 6 quasars. We find a 3σ tension between the observed and predicted X-ray-to-UV flux ratios when adopting the magnification probability distribution required to produce a µ = 450 quasar.