Abstract :
I review observational data on X-ray energy spectra and variability of Seyfert 1 and Narrow Line Seyfert 1 galaxies, and compare them to black hole binary (BHB) systems. There seems to be greater similarity of time averaged properties (i.e. energy spectra) than time variability between the supermassive and stellar-mass black hole accreting systems.
Energy spectra of Seyfert 1 galaxies are similar to BHB in low/hard state, but power spectra of Sy 1 are intermediate in properties between those for hard and soft states of BHB.
There is growing evidence that NLSy 1 are accreting at higher accretion rate than Sy 1, which supports the view that they correspond to soft states of BHB. Again, they are more similar to their stellar counterparts with respect to their spectral properties than to timing properties.
I briefly outline some theoretical ideas which suggest explanations of those differences.
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