Physics
Scientific paper
Feb 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...457..813k&link_type=abstract
Astrophysical Journal v.457, p.813
Physics
3
Accretion, Accretion Disks, Black Hole Physics, Radiation Mechanisms: Nonthermal, Radiation Mechanisms: Thermal
Scientific paper
A model for X-ray and gamma-ray emitting regions around black holes is presented. We assume that the emission regions are optically thin accretion disks where not only thermal processes but also nonthermal processes are important to disk structure and emission properties; we include nonthermal electron injection, soft photon injection, e+e- pair production, and subsequent pair cascades as well as radiation processes such as Compton scattering, bremsstrahlung, and pair annihilation. The emission spectrum from a disk is well described by a power law produced by thermal and nonthermal Compton scatterings. The power-law index αχ of X-rays is nearly independent of the mass accretion rate if lsoft/l is constant, where αχ is defined as Fυ ∝ υαχ, with Fυ being the energy spectrum, lsoft is the compactness of the injected soft photons, and l is the compactness of released gravitational energy due to mass accretion. For example, αχ is about -0.8 and -2.0, when lsoft/l = 0.2 and 2, respectively. Our model with a small lsoft/l (< 1) is promising to explain the low state observed from Galactic black hole candidates. Application of our model to Galactic black hole candidates, GX 339-4 and Cyg X-1, is shown as an example.
Next, the effects of pair escape on disk structure are studied. Pair escape decreases pair density, and escaping pairs carry away thermal energy. However, these effects on the disk structure are minor. Finally, advective cooling/heating on disk structure as well as the general relativistic effects on emission spectra are shown.
Kusunose Masaaki
Mineshige Shin
Yamada Tetsuya T.
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