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arXiv · 1803.08105

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

E. Bañados·T. Connor·D. Stern·J. Mulchaey·X. Fan·R. Decarli·E. P. Farina·C. Mazzucchelli·B. P. Venemans·F. Walter·F. Wang·J. Yang
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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.

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E. Bañados, T. Connor, D. Stern, J. Mulchaey, X. Fan, R. Decarli, E. P. Farina, C. Mazzucchelli, B. P. Venemans, F. Walter, F. Wang, J. Yang. 2018-03-21. Chandra X-rays from the redshift 7.54 quasar ULAS J1342+0928. https://doi.org/10.3847/2041-8213%2Faab61e

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