Farina, Emanuele P.
Venemans, B. P.
AffiliationUniv Arizona, Steward Observ
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PublisherIOP PUBLISHING LTD
CitationEduardo Bañados et al 2018 ApJL 856 L25
JournalASTROPHYSICAL JOURNAL LETTERS
Rights© 2018. The American Astronomical Society. All rights reserved.
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AbstractWe present a 45 ks Chandra observation of the quasar ULAS J1342+0928 at z=7.54. We detect 14.0(-3.7)(+4.8) 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(-0.28)(+0.26) 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(-0.53)(+0.55). 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 L2-10 = 11.6(-3.5)(+4.3) x 10(44) erg s(-1). Its X-ray-to-optical power-law slope is alpha(OX) = -1.67(-0.10)(+0.16), 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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