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

We review broad-band X-ray/gamma-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 K alpha line, low-energy absorption by cold matter, and a high-energy cutoff above similar to 200 keV. The X-ray energy spectral index, ct, is in the range similar to 0.8-1 in the average Seyfert-1 spectra from Ginga, EXOSAT and OSSE and in the available X-ray/gamma-ray spectra of bright Seyfert 1s. The low-state spectra of Cyg X-1 and GX 339-4 from simultaneous Ginga/OSSE observations have alpha similar or equal to 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 similar to (0.4-0.8) X 2 pi as seen from the X-ray source. Cutoffs in soft gamma-rays correspond to the plasma temperature of order of 100 keV. The intrinsic spectra are well explained by thermal Comptonization in plasmas with the Thomson optical depth of tau similar to 1.