The canonical X-ray/gamma-ray spectrum of Seyfert 1s and low-state Galactic black hole candidates.

Abstract

We review broad-band X-ray/γ-ray spectra of radio-quiet Seyfert 1s as well as of Galactic black hole candidates in the low state. The spectra share their basic components: an underlying power law, a Compton-reflection component with an Fe Kα line, low-energy absorption by cold matter, and a high-energy cutoff above ~200keV. The X-ray energy spectral index, α, is in the range ~0.8-1 in the average Seyfert-1 spectra from Ginga , EXOSAT and OSSE and in the available X-ray/γ-ray spectra of bright Seyfert 1s. The low-state spectra of Cyg X-1 and GX 339-4 from simultaneous Ginga /OSSE observations have α=~0.6-0.8. The Compton-reflection component corresponds to cold matter (e.g., inner or outer parts of an accretion disk) covering a solid angle of ~(0.4-0.8)x2π as seen from the X-ray source. Cutoffs in soft γ-rays correspond to the plasma temperature of order of 100keV. The intrinsic spectra are well explained by thermal Comptonization in plasmas with the Thomson optical depth of τ~1.