X-ray Variability of AGNs and Black Hole Masses

K. Hayashida$^1$ 


$^1$Osaka University, Toyonaka, Osaka, Japan\newline



X-ray light-curves of AGNs are characterized by random aperiodic
variability. We focus on the scaling relation of the variability
time scale of AGNs derived from their X-ray light-curves, 
so that it is used for estimation of 
central black hole masses (Hayashida et al., 1998, ApJ, 500, p.642). 
The basic assumptions we made are similarity of the X-ray variability 
for stellar mass BHs and AGNs, and linear proportionality of BH mass 
to the variability time scale we defined.  
We apply the method to various kinds of sources, getting the results 
like 1) Eddignton ratio of the typical (broad line) Seyfert 1
is about 0.1-1, 2) narrow line Seyfert 1 galaxies have $10^5$-$10^7$ 
solar masses, while broad line Seyfert 1 do $10^7$-$10^8$ solar masses, 
3) low luminosity AGNs, such as LINERs,
contain BH of $10^6$ solar masses or larger. 
In order to verify our mass estimation, we refer to the BH masses
estimated through the broad line reverberation mapping.   
It is found that masses by our method agree within one order of 
magnitude with those obtained in the broad line method. \\
Nevertheless, the length of the AGN X-ray light-curves investigated so far
has been limited to days in most cases, and the time scales investigated 
have ranged from minutes to days.  The MAXI experiment will enlarge the longer time scale side of this range significantly for number of sources. 
In this paper, we would also illustrate significance of the MAXI experiment on 
the AGN studies regarding this point, based on our view of the scaling relation of the X-ray variability.