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High-redshift radio-quiet quasars : exploring the parameter space of accretion models : I : hot semispherical flow.

Sobolewska, M. A. and Siemiginowska, A. and Zycki, P. T. (2004) 'High-redshift radio-quiet quasars : exploring the parameter space of accretion models : I : hot semispherical flow.', Astrophysical journal., 608 (1). pp. 80-94.


Two families of models are currently considered to describe an accretion flow onto black holes and production of the observed X-ray radiation: (1) a standard cold accretion disk with a hot corona above it and (2) an outer truncated accretion disk with a hot semispherical inner flow. We compute spectra in the scenario with a hot inner flow surrounded by a truncated accretion disk covered by a hot corona and test the results on a sample of high-redshift (z > 4) quasars observed with Chandra. We find that in order to reproduce the ratio of optical to X-ray fluxes (the ox parameter), the optical depth of the Comptonizing plasma has to be rather low ( = 0.020.25 in the corona above the disk, and = 0.100.70 in the hot inner flow). This, together with the observed X-ray photon indices, implies either a high temperature in a thermal plasma (kTe = 90500 keV) or a nonthermal electron distribution in the plasma. We put an upper limit on the disk truncation radius, rtr 40RS. The modeled accretion rate is high, > 0.2Edd, which may suggest that high-z radio-quiet quasars are analogs of X-ray binaries in their high or very high state.

Item Type:Article
Keywords:Accretion disks, Galaxies, High-redshift quasars, X-rays.
Full text:Full text not available from this repository.
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Record Created:20 May 2008
Last Modified:15 Mar 2011 12:33

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