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Title: Exploratory X-ray monitoring of luminous radio-quiet quasars at high redshift: Initial results

We present initial results from an exploratory X-ray monitoring project of two groups of comparably luminous radio-quiet quasars (RQQs). The first consists of four sources at 4.10 ≤ z ≤ 4.35, monitored by Chandra, and the second is a comparison sample of three sources at 1.33 ≤ z ≤ 2.74, monitored by Swift. Together with archival X-ray data, the total rest-frame temporal baseline spans ∼2-4 yr and ∼5-13 yr for the first and second group, respectively. Six of these sources show significant X-ray variability over rest-frame timescales of ∼10{sup 2}-10{sup 3} days; three of these also show significant X-ray variability on rest-frame timescales of ∼1-10 days. The X-ray variability properties of our variable sources are similar to those exhibited by nearby and far less luminous active galactic nuclei (AGNs). While we do not directly detect a trend of increasing X-ray variability with redshift, we do confirm previous reports of luminous AGNs exhibiting X-ray variability above that expected from their luminosities, based on simplistic extrapolation from lower luminosity sources. This result may be attributed to luminous sources at the highest redshifts having relatively high accretion rates. Complementary UV-optical monitoring of our sources shows that variations in their optical-X-ray spectral energy distributionmore » are dominated by the X-ray variations. We confirm previous reports of X-ray spectral variations in one of our sources, HS 1700+6416, but do not detect such variations in any of our other sources in spite of X-ray flux variations of up to a factor of ∼4. This project is designed to provide a basic assessment of the X-ray variability properties of RQQs at the highest accessible redshifts that will serve as a benchmark for more systematic monitoring of such sources with future X-ray missions.« less
Authors:
;  [1] ; ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7]
  1. Department of Physics, University of North Texas, Denton, TX 76203 (United States)
  2. Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)
  3. Dipartimento di Scienze Fisiche, Università Federico II di Napoli, via Cinthia 6, I-80126 Napoli (Italy)
  4. School of Physics and Astronomy and the Wise Observatory, Tel Aviv University, Tel Aviv 69978 (Israel)
  5. Dipartimento di Astronomia, Università degli studi di Bologna, via Ranzani 1, I-40127 Bologna (Italy)
  6. Departamento de Astronomia, Universidad de Chile, Camino del Observatorio 1515, Santiago (Chile)
  7. Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)
Publication Date:
OSTI Identifier:
22351576
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 783; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BENCHMARKS; COMPARATIVE EVALUATIONS; DESIGN; ENERGY SPECTRA; EXTRAPOLATION; GALAXY NUCLEI; LUMINOSITY; QUASARS; RED SHIFT; X RADIATION; X-RAY GALAXIES