A chandra snapshot survey of representative high-redshift radio-loud quasars from the parkes-MIT-NRAO sample

L. A. Lopez, W. N. Brandt, C. Vignali, D. P. Schneider, G. Chartas, G. P. Garmire

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15 Scopus citations


We present the results of Chandra ACIS-S snapshot observations of six radio-loud quasars (RLQs) at z ≈ 3.5-4.7. These observations sample luminous RLQs with moderate to high radio loudness (R ≈ 200-9600) and aim to connect the X-ray properties of radio-quiet quasars (R < 10) and highly radio-loud blazars (R > 1000) at high redshift. This work extends a study by Bassett and coworkers that used similar methods to examine z > 4 RLQs with moderate radio loudness (R ≈ 40-400). All of our targets are clearly detected. A search for extended X-ray emission associated with kiloparsec-scale radio jets revealed only limited evidence for X-ray extension in our sample: three sources showed no evidence of X-ray extension, and the other three had 3%-30% of their total X-ray fluxes extended >1″ away from their X-ray cores. In addition, we do not observe any systematic flattening of the optical-to-X-ray spectral index (α ox) compared to low-redshift quasars. These results suggest that kiloparsec-scale X-ray jet emission is not dominated by inverse Compton scattering of cosmic microwave background seed photons offjet electrons. We measured X-ray continuum shapes and performed individual and joint spectral fits of our data combined with eight archival RLQs. A single power-law model acceptably fitted the data, with best-fit photon indices of 1.72 -0.12 +0.11 for moderate-R sources and 1.47 -0.12 +0.13 for high-R sources. We added an intrinsic absorption component to our model, and neither the moderate-R nor the high-R fits set a lower bound on N H. The upper limits were N H < 3.0×10 22 cm -2 and N H < 2.8 × 10 22 cm -2, respectively. Our spectral results suggest that intrinsic absorption does not strongly depend on radio loudness, and high-R sources have flatter power laws than moderate-R sources. Overall, our high-redshift RLQs have basic X-ray properties consistent with similar RLQs in the local universe.

Original languageEnglish (US)
Pages (from-to)1914-1922
Number of pages9
JournalAstronomical Journal
Issue number4
StatePublished - Apr 2006

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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