ASCA observations of NLS1s: BH mass estimation from X-ray variability and X-ray spectra

Abstract ASCA observations of Narrow-Line Seyfert 1 galaxies (NLS1s) are presented. We focus on the black hole size of the NLS1 sources by employing two independent methods for the mass estimation; one is using X-ray variability, the other is using a blackbody fit to the soft component. Although the coincidence is not good for some sources, the mass estimated by these methods ranges from 10 5 to 10 7 M ⊙ , systematically smaller than those for typical (broad line) Seyfert 1. We consider the small mass black hole to be the principal cause of the several extreme characteristics of the NLS1s.