3. Data analysis: general assumptions
Several models were applied to the X-ray spectra of the galaxies: (i) a single powerlaw of the form (which, even if not the correct description, always provides a useful means of judging the steepness of the spectrum), (ii) a powerlaw plus soft excess parameterized either as black body emission or by the accretion disk model available in EXSAS (Zimmermann et al. 1994), and (iii) a warm absorber model. The latter was calculated with Ferland's (1993) code Cloudy (see Komossa & Fink 1997a,b for details). The following assumptions were made: The warm absorber is assumed to be of constant density , of solar abundances according to Grevesse & Anders (1989) (if not mentioned otherwise), and to be illuminated by the continuum of the central point-like energy source. The spectral energy distribution from the radio to the gamma-ray region consists of our mean AGN continuum (Komossa & Schulz 1997) of piecewise powerlaws with, in particular, an energy index in the EUV and an X-ray photon index which is either directly determined from X-ray spectral fits or fixed to -1.9. The fit parameters of the warm absorber are its column density and the ionization parameter . In case of the dusty warm absorber models the dust composition and grain size distribution were chosen like in the Galactic diffuse interstellar medium (Mathis et al. 1977) as incorporated in Cloudy (Ferland 1993), and the metal abundances were depleted correspondingly (see Komossa & Fink 1997b,c for details).
© European Southern Observatory (ESO) 2000
Online publication: February 9, 2000