Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aipc..599.1003w&link_type=abstract
X-RAY ASTRONOMY: Stellar Endpoints,AGN, and the Diffuse X-ray Background. Edited by Nicholas E. White, Giuseppe Malaguti, and G
Astronomy and Astrophysics
Astronomy
Active And Peculiar Galaxies And Related Systems, X-Ray Sources, X-Ray Bursts, Radiative Transfer, Scattering
Scientific paper
Seyfert galaxies have been shown to exhibit a rich variety in terms of their X-ray spectra. One process which contributes in the soft X-ray band is the scattering of the continuum flux by highly ionized gas in the vicinity of the nucleus. This is particularly important in systems where the direct view of the continuum source is blocked below a few keV by line-of-sight absorption, in which case the scattered component is often apparent as a soft excess flux. A spectral feature observed near 0.9 keV in the X-ray spectra of several such Seyfert galaxies, including NGC 4151, can be interpreted as OVIII recombination originating in a warm, partially photoionized, scattering medium. We find that, in the case of NGC 4151, the electron scattering medium may be highly stratified with the warm (Twarm~3×105 K) plasma representing only a minor component in comparison to hotter (Thot>~107 K), more highly photoionized gas. Nevertheless it appears that the recombination continua of the hydrogen-and helium-like ions of elements such as oxygen, silicon and sulphur may, in future X-ray observations, provide an important new diagnostic of the temperature, the ionization state and conceivably the dynamics of the electron scattering media present in Seyfert nuclei. .
Griffiths Gareth R.
Warwick Robert S.
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