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We present a 45 ks Chandra observation of the quasar ULAS J1342+0928 atz=7.54. We detect 14.0^{+4.8}_{-3.7} counts from the quasar in theobserved-frame energy range 0.5-7.0 keV (6-sigma detection), representing themost distant non-transient astronomical source identified in X-rays to date.The present data are sufficient only to infer rough constraints on the spectralparameters. We find an X-ray hardness ratio of 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 photonindex of Gamma = 1.95^{+0.55}_{-0.53}. Assuming a typical value forhigh-redshift quasars of Gamma = 1.9, ULAS J1342+0928 has a 2-10 keV rest-frameX-ray luminosity of L_{2-10} = 11.6^{+4.3}_{-3.5} x 10^{44} erg/s. ItsX-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 themost bolometrically powerful quasars is weaker relative to their opticalemission.

Chandra X-rays from the redshift 7.54 quasar ULAS J1342+0928