1999MNRAS.310...10G

We present an X-ray spectroscopic study of the bright Compton-thick Seyfert 2 galaxies NGC 1068 and the Circinus Galaxy, performed with BeppoSAX. Matt et al. interpreted the spectrum above 4keV as the superposition of Compton reflection and warm plasma scattering of the nuclear radiation. When this continuum is extrapolated downwards to 0.1keV, further components arise. The NGC 1068 spectrum is rich in emission lines, mainly owing to K_α transitions of He-like elements from oxygen to iron, plus a K_α fluorescent line from neutral iron. If the ionized lines originate in the warm scatterer, its thermal and ionization structure must be complex. From the continuum and line properties, we estimate a column density, N_warm, of the warm scatterer less than a fewx10²¹cm^–2. In the Circinus Galaxy, the absence of highly ionized iron is consistent with a scattering medium with U_X≲5 and N_warm∼ a fewx10²²cm^–2. In both cases the neutral iron line is most naturally explained as fluorescence in the medium responsible for the Compton reflection continuum. In NGC 1068 an optically thin plasma emission with kT≃500eV and strongly sub-solar metallicity is required, while such a component is only marginal in the Circinus Galaxy. We tentatively identify this component as emission of diffuse hot gas in the nuclear starbursts. Possible causes for the metal depletion are discussed.