Two different accretion classes in Seyfert 1 galaxies and QSOs

The mass of the central black holes in Seyfert galaxies and QSOs can be det ermined from the broad emission lines and the reverberation method. Using t he measured black hole mass and the bolometric or ionizing luminosity, the accretion rate can be estimated. Compiling a sample of Seyfert 1 galaxies a nd QSOs with reliable central masses, estimated ionizing luminosities, and X-ray spectral slopes, we find that the X-ray spectral slope strongly corre lates with the accretion rate. The objects in the sample are found to be di stributed in two distinct classes in the spectral index versus log (L-ion/L -Edd)-plane. We argue that these two classes may correspond to advection-do minated accretion flow (ADAF) and thin disk accretion. The observations of a "two-state" Seyfert 1 galaxy, 1H 0419-577, confirm our results. Detailed fitting of the spectra of individual Seyfert 1 galaxies and QSOs using ADAF and/or thin disk models should further clarify the two-class classificatio n.