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

B.P. Venemans; C. Mazzucchelli; D. Stern; E. Ba\~nados; E.P. Farina; F. Walter; F. Wang; J. Mulchaey; J. Yang; R. Decarli

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

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arxiv 1803.08105 v1 pith:5OZ4THO4 submitted 2018-03-21 astro-ph.GA

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

E. Ba\~nados , T. Connor , D. Stern , J. Mulchaey , X. Fan , R. Decarli , E.P. Farina , C. Mazzucchelli

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B.P. Venemans F. Walter F. Wang J. Yang

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keywords j1342quasarulasx-raychandraemissiongammapower-law

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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.

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