X-ray variability and soft X-ray spectrum of narrow line Seyfert 1 sources

ASCA observations of narrow line Seyfert 1 galaxies (NLS1) 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 blackbody fit to the soft component. Although the coincidence is not good for some sources, the mass estimated in these ways ranges from 10(4) to 10(7) M-circle dot, systematically smaller than those for typical (broad line) Seyfert 1. We consider the small mass black hole is the principal cause of the several extreme characteristics of the NLS1s. We also mention the emission line model for the X-ray spectral features found in some NLS1 sources. (C) 2000 COSPAR. Published by Elsevier Science Ltd.