1995/10/31 by Sandip K. Chakrabarti, Sandip Chakrabarti, Lev G. Titarchuk · 532 citations
Physics and Astronomy · #Accretion (finance) #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Black hole (networking) #Bremsstrahlung #Galaxies: Formation, Evolution, Phenomena #Halo #Radiative transfer #Schwarzschild radius #Soft photon #Spectral line #astro-ph
paper · pdf · doi:10.1086/176610
published in The Astrophysical Journal 455, 623 (IOP Publishing) · 45 pages of Latex file + 10 figures (Misprints in Description and Caption of Figure 2 are corrected)
openalex publication_date 1995/12/01 · arxiv created 1996/01/31 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
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 = r<SUB>s</SUB>: (1) An optically thick Keplerian disk on the equatorial plane (r > r<SUB>s</SUB>); (2) a sub-Keplerian optically thin halo above and below this disk r > r<SUB>s</SUB> and (3) a hot, optically slim τ ∼ 1 postshock region r < r<SUB>s</SUB> ∼ 5-10r<SUB>g</SUB> where r<SUB>g</SUB> 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.