We present a 45 ks Chandra observation of the quasar ULAS J1342+0928 at z = 7.54 .
We detect 14.0 ^ { +4.8 } _ { -3.7 } counts from the quasar in the observed-frame energy range 0.5–7.0 keV ( 6 \sigma detection ) , representing the most distant non-transient astronomical source identified in X-rays to date .
The present data are sufficient only to infer rough constraints on the spectral parameters .
We find an X-ray hardness ratio of \mathcal { HR } = -0.51 ^ { +0.26 } _ { -0.28 } between the 0.5–2.0 keV and 2.0–7.0 keV ranges and derive a power-law photon index of \Gamma = 1.95 ^ { +0.55 } _ { -0.53 } .
Assuming a typical value for high-redshift quasars of \Gamma = 1.9 , ULAS J1342+0928 has a 2–10 keV rest-frame X-ray luminosity of L _ { 2 - 10 } = 11.6 ^ { +4.3 } _ { -3.5 } \times 10 ^ { 44 } { erg } { s } ^ { -1 } .
Its X-ray-to-optical power-law slope is \alpha _ { OX } = -1.67 ^ { +0.16 } _ { -0.10 } , consistent with the general trend indicating that the X-ray emission in the most bolometrically powerful quasars is weaker relative to their optical emission .