NLS1 galaxies and estimation of their central black hole masses from the X-ray excess variance method

Black hole mass determination in active galaxies is a key issue ill Understanding, Various luminosity states. In the present paper, we try to generalize the mass determination method based oil the X-ray excess variance, successfully used for typical broad line Seylert I galaxies (BLS1) to narrow line Seyfert 1 (NLS I) galaxies. NLS I galaxies differ from BLS I with respect to several properties. They are generally more variable in 2-10 keV energy hand so the natural expectation is the need to use a different scaling coefficient between the mass and the variance in these two types of Sources. However, we find that Such a simple approach is not enough. Although for majority of the 2 1 NLS I galaxies in Our sample a single scaling coefficient (larger by a factor 20) provided LIS With a satisfactory method of mass determination, in a Small Subset of NLS I galaxies this approach failed. Variability of those objects appeared to he at the intermediate level between NLS I and BLS I galaxies. These exceptional NLS I galaxies have much harder soft X-ray spectra than majority of NLS I galaxies. We thus postulate that the division of Seyfert I galaxies into BLS I and NLS I according to the widths of the H line is less, generic than according to the soft X-ray slope.