X-rays from the redshift 7.1 quasar ULAS J1120+0641

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 ± 0.9 × 1044 erg s−1 and a spectral slope α=1.6+0.4−0.3 (where fν ∝ ν−α). The quasar appears to have dimmed in the 15 months between the two observations, with a 2–10 keV luminosity of 1.8+1.0−0.7×1045 erg s−1 during the Chandra observation. We derive optical-to-X-ray spectral slopes αOX of 1.76 ± 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 αOX 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/LEdd=5+15−4, compared to L/LEdd=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 ( 1.46 has been maintained over the quasar's lifetime.This is the final published version. It originally appeared in MNRAS at http://mnrasl.oxfordjournals.org/content/440/1/L91