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

Sobolewska, M.A.; Siemiginowska, A.; Zycki, P.T.

Abstract

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.

Citation

Sobolewska, M., Siemiginowska, A., & Zycki, P. (2004). High-redshift radio-quiet quasars: Exploring the parameter space of accretion models. I. Hot semispherical flow. Astrophysical Journal, 608(1), 80-94. https://doi.org/10.1086/392529

• Journal Article Type: Article
• Publication Date: 2004-06
• Deposit Date: May 20, 2008
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 608
• Issue: 1
• Pages: 80-94
• DOI: https://doi.org/10.1086/392529
• Keywords: Accretion disks, Galaxies, High-redshift quasars, X-rays.
• Public URL: https://durham-repository.worktribe.com/output/1580984