Chandra X-Rays from the Redshift 7.54 Quasar ULAS J1342+0928

Eduardo Banados, Thomas Connor, Daniel Stern, John Mulchaey, Xiaohui Fan, Roberto Decarli, Emanuele P. Farina, Chiara Mazzucchelli, Bram P. Venemans, Fabian Walter, Feige Wang, Jinyi Yang

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


We present a 45 ks Chandra observation of the quasar ULAS J1342+0928 at z = 7.54. We detect counts from the quasar in the observed-frame energy range 0.5-7.0 keV (6σ 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 between the 0.5-2.0 keV and 2.0-7.0 keV ranges and derive a power-law photon index of . Assuming a typical value for high-redshift quasars of Γ = 1.9, ULAS J1342+0928 has a 2-10 keV rest-frame X-ray luminosity of . Its X-ray-to-optical power-law slope is , consistent with the general trend indicating that the X-ray emission in the most bolometrically powerful quasars is weaker relative to their optical emission.

Original languageEnglish (US)
Article numberL25
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Apr 1 2018


  • cosmology
  • individual (ULAS J134208.10+092838.61)
  • observations-early universe-quasars

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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