We present X-ray imaging and spectroscopy of the redshift z = 7.084 radio-quiet quasar ULAS J112001.48+064124.3 obtained with Chandra and XMM-Newton .
The quasar is detected as a point source with both observatories .
The Chandra observation provides a precise position , confirming the association of the X-ray source and the quasar , while a sufficient number of photons is detected in the XMM-Newton observation to yield a meaningful X-ray spectrum .
In the XMM-Newton observation the quasar has a 2-10 keV luminosity of 4.7 \pm 0.9 \times 10 ^ { 44 } erg s ^ { -1 } and a spectral slope \alpha = 1.6 ^ { +0.4 } _ { -0.3 } ( where f _ { \nu } \propto \nu ^ { - \alpha } ) .
The quasar appears to have dimmed in the 15 months between the two observations , with a 2-10 keV luminosity of 1.8 ^ { +1.0 } _ { -0.7 } \times 10 ^ { 45 } erg s ^ { -1 } during the Chandra observation .
We derive optical to X-ray spectral slopes \alpha _ { OX } of 1.76 \pm 0.07 and 1.54 ^ { +0.09 } _ { -0.08 } at the times of the XMM-Newton and Chandra observations respectively , consistent with the range of \alpha _ { OX } found in other quasars of comparable ultraviolet luminosity .
The very soft X-ray spectrum suggests that the quasar is accreting above the Eddington rate , L / L _ { Edd } = 5 ^ { +15 } _ { -4 } , compared to L / L _ { Edd } = 1.2 ^ { +0.6 } _ { -0.5 } derived from the rest-frame ultraviolet .
Super-Eddington accretion would help to reduce the discrepancy between the age of the quasar implied by the small size of the ionized near zone in which it sits ( < 10 ^ { 7 } years ) , and the characteristic e-folding time ( 2.5 \times 10 ^ { 7 } years if L / L _ { Edd } = 2 ) .
Such super-Eddington accretion would also alleviate the challenging constraints on the seed black hole mass provided that the quasar has been rapidly accreting throughout its history .
The remnant of an individual population III star is a plausible progenitor if an average L / L _ { Edd } > 1.46 has been maintained over the quasar ’ s lifetime .