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CHANDRA OBSERVATIONS OF RADIO-LOUD QUASARS AT Z > 4: X-RAYS FROM THE RADIO BEACONS OF THE EARLY UNIVERSE

We present the results of Chandra observations of six radio-loud quasars (RLQs) and one optically bright radioquiet quasar (RQQ) at z ≈ 4.1–4.4. These observations cover a representative sample of RLQs with moderate radio-loudness (R ≈ 40–400), filling the X-ray observational gap between optically selected radio-quiet quasars (predominantly R ∼< 2–10) and the five known blazars at z > 4 (R ≈ 800–27000), where R= f5 GHz/ f4400 Å (rest frame). We study the relationship between X-ray luminosity and radio-loudness for quasars at high redshift and constrain RLQ X-ray continuum emission and absorption. From a joint spectral fit of nine moderate-R RLQs observed by Chandra, we find tentative evidence for absorption above the Galactic NH , with a best-fit neutral intrinsic column density of NH = 2.4+2.0 −1.8 ×10 22 cm−2, consistent with earlier claims of increased absorption toward high-redshift RLQs. We also search for evidence of an enhanced jet-linked component in the X-ray emission due to the increased energy density of the cosmic microwave background (CMB) at high redshift, but we find neither spatial detections of X-ray jets nor a significant enhancement in the X-ray emission relative to comparable RLQs at low-to-moderate redshifts. Overall, the z ≈ 4–5 RLQs have basic X-ray properties consistent with comparable RLQs in the local universe, suggesting that the accretion/jet mechanisms of these objects are similar as well. Subject headings: galaxies: active — galaxies: high-redshift — galaxies: jets — galaxies: nuclei — quasars: general