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

TL;DR

This paper reports the first X-ray detection of a very distant quasar at redshift 7.54 using Chandra, providing insights into its high-energy emission and properties in the early universe.

Contribution

First X-ray observation of a z=7.54 quasar, establishing its X-ray luminosity and spectral characteristics, and extending knowledge of high-redshift quasar emissions.

Findings

Detected X-ray emission from the quasar at z=7.54.

Derived spectral parameters consistent with lower-redshift quasars.

X-ray-to-optical slope aligns with known quasar trends.

Abstract

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 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} x 10^{44} erg/s. 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.