A multizone model for composite disk-corona structure and spectral formation in active galactic nuclei

Details A multizone model for composite disk-corona structure and spectral formation in active galactic nuclei A multizone model for composite disk-corona structure and spectral formation in active galactic nuclei

Jan 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...439...74s&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 439, no. 1, p. 74-79

Other

9

Accretion Disks, Active Galactic Nuclei, Energy Budgets, Galactic Structure, Hydrostatics, Radiative Transfer, Ultraviolet Spectra, Equations Of State, Equilibrium Equations, Mathematical Models, Power Spectra, Temperature Profiles

Scientific paper

We study a composite disk-corona structure in active galactic nuclei (AGN) by solving for radiative transfer, hydrostatic balance, and energy balance at each layer with a different vertical height. A key assumption is that a fraction f of total energy is dissipated in a corona with a Thomson optical depth of tauC, and a remaining fraction, 1-f, within a main body of the disk. As f increases, a two-phased structure grows with an abrupt temperature jump at the interface. As a result, the emergent spectrum varies from a blackbody-like spectrum to a power-law spectrum with a high-energy cutoff. The power-law index is insensitive to a mass of a central black hole, accretion rate, and tauC, and decreases with an increase of f, reaching approximately 0.9 for f approximately = 1. The cutoff energy (Ecutoff) is, on the other hand, related to tauC as tauC Ecutoff approximately = 90 keV. The radiative field is a blackbody at the midplane of the disk, but has a power-law energy distribution near the surface due to a reflection of high-energy photons emanating from the corona. The resultant spectra thus produce litle UV bumps. To account for the observed AGN spectra, therefore, we should consider more complicated situations such as a partial coverage of hot corona and an effect of absorption by heavy elements.

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