X-RAY-EMISSION OF SEYFERT-1 GALAXIES - THE ORIGIN OF THE POSITIVE CORRELATION BETWEEN FLUX AND SPECTRAL INDEX

We investigate the positive correlation between the X-ray flux in the 2-10 keV band and the spectral index in the same spectral band observe d in some Seyfert 1 galaxies. We propose that inverse Compton scatteri ng of UV thermal photons by a population of non thermal relativistic e lectrons be the origin of this emission. Both the thermal UV emission and the Compton reprocessing take place inside the same plasma cloud. The cloud thermodynamical parameters as well as the properties of the relativistic electron distribution are selfconsistently derived in ter ms of the experimental data (UV luminosity, flux, spectral index and t imescale varibility in the X-ray domain). The observed trend between t he flux and the spectral index is well reproduced if the number of rel ativistic electrons efficient in the inverse Compton scattering is con stant and if the cloud temperature is of the order of 3 10(5) K.