A quasi-spherical inner accretion flow in Seyfert galaxies.

We study a phenomenological model for the continuum emission of Seyfert galaxies. In this quasi-spherical accretion scenario, the central X-ray source is constituted by a hot spherical plasma region surrounded by spherically distributed cold dense clouds. The cold material is radiatively coupled with the hot thermal plasma. Assuming energy balance, we compute the hard X-ray spectral slope ⌈ and reflection amplitude R. This simple model enables us to reproduce both the range of observed hard X-ray spectral slopes, and reflection amplitude R. It also predicts a correlation between R and ⌈ which is very close to what is observed. Wide changes in the cloud covering fraction from source to source would be reponsible for most of the observed spectral variations. Moreover, if some internal dissipation process is active in the cold clouds, obscuration effects may provide a simple explanation for the observed distributions of reflection amplitudes, spectral slopes, and UV to X-ray flux ratios. [ABSTRACT FROM AUTHOR]