The Variability MCG-6-30-15 as Deduced from Chandra HETG Spectra

Marshall H.L.$^1$, Lee J.C.$^1$, Canizares C.R.$^1$, Ogle P.M.$^2$,
Fabian A.C.$^3$, Morales R.$^3$, Iwasawa K.$^3$

$^1$Center for Space Research, MIT, Cambridge, MA, USA\newline
$^2$U. California, Santa Barbara, CA, USA\newline
$^3$Institute of Astronomy, Cambridge, UK


Spectral variability studies are key for understanding the physical
processes governing the environment of AGNs.   One of the best studied
examples is the canonical Seyfert~1 galaxy MCG-6-30-15, which exhibits
variability over a wide energy range, from the warm absorber region, to
the iron line (in profile and amplitude), as well as direct and
reflected power law compoents.  We assess the ionization conditions of
the warm absorber deduced from Chandra HETG spectra of MCG--6-30-15
in different flux states.   We found many absorption features
that they change with the flux of the source, providing diagnostics
of the conditions of the source and its environs.  From the models
of the warm absorber and the flux of the O VII emission line, we
estimate that the average X-ray flux of MCG--6-30-15 over the past
100 years is not greatly different from that observed today.