Estimation of Central Black Hole masses in Low-luminosity AGNs 



Awaki H.$^{1,5}$, Sakano H.$^2$, Terashima Y.$^3$, and Hayashida K.$^{4,5}$



$^1$Ehime University, Matsuyama, Ehime, Japan\newline
$^2$NSADA, Tsukuba, Ibaragi, Japan\newline
$^3$NASA/GSFC, Code 662, Greenbelt, MD,USA\newline
$^4$Osaka University, Toyonaka, Osaka, Japan\newline
$^5$ Japan Science and Technology Corporation (JST), Kawaguchi, Saitama, Japan\newline



  We analyzed two bright LINERs (low-ionization nuclear emission line region) 
with broad $H_{\rm{\alpha}}$ lines, and four bright low-luminosity Seyferts observed by 
the X-ray satellite ASCA. We examined the time variability for these targets, 
and found that most targets show no significant time variability although
these galaxies have weak AGN activities.  By applying Fourier analysis 
to their light curves in the 2--10keV band, we obtained the lower limit of
their time variability scale, which corresponds to their central black hole 
masses of greater than several times of 10$^{6}{M_{\bullet\hspace{-5.2pt}\odot}}$.
Our result suggests that these low-luminosity objects are harbors 
of super massive black holes.  Their mass accretion rate is estimated to be
$<$ 10$^{-3} {M_{\bullet\hspace{-5.2pt}\odot}}$/yr, which is too small to create such super massive black 
holes in Hubble time.  Therefore, we concluded that the mass accretion rates 
in the past must have been larger than those at present, and that these 
galaxies were probably as luminous as QSOs in the past.