We study the spectral properties of a very general class of accretion disks which can be decomposed into three distinct components apart from a shock at r = rs: (1) An optically thick Keplerian disk on the equatorial plane (r > rs); (2) a sub-Keplerian optically thin halo above and below this disk r > rs and (3) a hot, optically slim τ ∼ 1 postshock region r < rs ∼ 5-10rg where rg is the Schwarzschild radius. The postshock halo intercepts soft photons from the Keplerian component and reradiates them as hard X-rays and γ rays after Comptonization. We solve two-temperature equations in the postshock region with Coulomb energy exchange between protons and electrons, and incorporating radiative processes such as bremsstrahlung and Comptonization. We also present the exact prescription to compute the reflection of the hard X-rays from the cool disk. We produce radiated spectra from both the disk components as functions of the accretion rates and compare them with the spectra of Galactic and extragalactic black hole candidates. We find that the transition from hard state to soft state is smoothly initiated by a single parameter, namely the mass accretion rate of the disk. In the soft state, when the postshock region is very optically thick and cooled down, bulk motion of the converging flow determines the spectral index to be about 1.5 in agreement with observations.

Spectral Properties of Accretion Disks around Galactic and Extragalactic Black Holes

TITARCHUK, Lev
1995

Abstract

We study the spectral properties of a very general class of accretion disks which can be decomposed into three distinct components apart from a shock at r = rs: (1) An optically thick Keplerian disk on the equatorial plane (r > rs); (2) a sub-Keplerian optically thin halo above and below this disk r > rs and (3) a hot, optically slim τ ∼ 1 postshock region r < rs ∼ 5-10rg where rg is the Schwarzschild radius. The postshock halo intercepts soft photons from the Keplerian component and reradiates them as hard X-rays and γ rays after Comptonization. We solve two-temperature equations in the postshock region with Coulomb energy exchange between protons and electrons, and incorporating radiative processes such as bremsstrahlung and Comptonization. We also present the exact prescription to compute the reflection of the hard X-rays from the cool disk. We produce radiated spectra from both the disk components as functions of the accretion rates and compare them with the spectra of Galactic and extragalactic black hole candidates. We find that the transition from hard state to soft state is smoothly initiated by a single parameter, namely the mass accretion rate of the disk. In the soft state, when the postshock region is very optically thick and cooled down, bulk motion of the converging flow determines the spectral index to be about 1.5 in agreement with observations.
S., Chakrabarti; Titarchuk, Lev
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11392/532907
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 456
  • ???jsp.display-item.citation.isi??? 466
social impact