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2005AJ....129.2519V - Astron. J., 129, 2519-2530 (2005/June-0)
X-ray lighthouses of the high-redshift universe. II. Further snapshot observations of the most luminous z≳4 quasars with Chandra.
VIGNALI C., BRANDT W.N., SCHNEIDER D.P. and KASPI S.
Abstract (from CDS):
We present joint X-ray spectral fitting for a sample of 48 radio-quiet quasars in the redshift range 3.99-6.28 for which Chandra observations are available. The X-ray spectrum (~870 counts) is well parameterized by a power law with Γ=1.93+0.10–0.09 in the rest-frame ~2-40 keV band, and a tight upper limit of NH~5x1021/cm2 is obtained on any average intrinsic X-ray absorption. There is no indication of any significant evolution in the X-ray properties of quasars between redshifts 0 and 6, suggesting that the physical processes of accretion onto massive black holes have not changed over the bulk of cosmic time.
Abstract Copyright: ∼
Journal keyword(s): Galaxies: Active - Galaxies: Nuclei - Galaxies: Quasars: General - X-Rays: Galaxies
Simbad objects: 24
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