SIMBAD references

The mass of the central black holes in Seyfert galaxies and QSOs can be determined from the broad emission lines and the reverberation method. Using the measured black hole mass and the bolometric or ionizing luminosity, the accretion rate can be estimated. Compiling a sample of Seyfert 1 galaxies and QSOs with reliable central masses, estimated ionizing luminosities, and X-ray spectral slopes, we find that the X-ray spectral slope strongly correlates with the accretion rate. The objects in the sample are found to be distributed 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-dominated 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 classification.