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Astron. Astrophys. 322, 719-729 (1997)

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6. Summary and conclusions

We detect the following spectral components in the Nov. 1993 spectrum of NGC 4051: A powerlaw in its steepest observed state with [FORMULA] = -2.3, modified by the presence of a warm absorber, and evidence for a black-body-like soft excess during the flux high-state with [FORMULA] 0.1 keV. The first two components are essentially constant during the observation, but significantly variable when compared to former observations. Mainly arguments on the number Q of ionizing photons and optical emission line ratios hint to a further bump component in the EUV.

The warm absorber component has been modeled in more detail, which yields a column density of [FORMULA] = 22.7 and an ionization parameter of [FORMULA] = 0.4 (from X-ray spectral fits), a limit on the density of [FORMULA] [FORMULA] cm-3 (from variability arguments) translating into a distance from the nucleus of [FORMULA] cm, and a covering that can be as large as 100 % (from emission line arguments). Observational evidence (no indications of strong reddening along the line of sight, e.g. from the UV spectrum) and model results (no successful X-ray fit) strongly suggest the absorber to be dust free.

Observable consequences of the existence of the ionized material in other spectral regions (in the form of emission or absorption lines) are found to be small: None of the observed emission line regions in NGC 4051 can be fully identified with the warm absorber. The possibility of a contribution to observed individual lines (that would complicate line intensity modeling or reverberation mapping), namely to HeII [FORMULA] 1640, remains in case of subsolar metal abundances of the absorber.

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© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998