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2002MNRAS.334..811S - Mon. Not. R. Astron. Soc., 334, 811-818 (2002/August-3)
Characterizing the complex absorber in NGC 4151.
SCHURCH N.J. and WARWICK R.S.
Abstract (from CDS):
The warm absorber in NGC 4151 has a column density of ∼2x1023 cm –2 , with an ionization parameter in the range log(ξ) ~ 2.4-2.7. The inferred relatively low density (∼105 cm–3 ) for the warm gas implies an equilibration time-scale for the dominant ions of the same order as or longer than the time-scale of the continuum variability. It follows that the warm component will invariably be observed in a non-equilibrium ionization state. The warm absorber in NGC 4151 may be identified as a multi-temperature wind produced by evaporation from the inner edge of an obscuring torus as discussed in a recent paper by Krolik & Kriss. The unusually complex character of the absorption seen in NGC 4151 may then be explained in terms of a fortuitous line of sight which grazes the top edge of the obscuring torus so as to intercept a substantial column of both the warm and cold gas.
We also find that (i) the reported hardening of the spectrum of NGC 4151 as the continuum level falls may be simply due to the presence of an underlying (hard and relatively constant) Compton-reflection component, and (ii) the iron Kα line has a relatively narrow Gaussian profile and a line flux that remains constant over both short (days) and long (months to years) time-scales-a relativistically broadened iron Kα feature was not required in our modelling.
Abstract Copyright: RAS
Journal keyword(s): galaxies: active - galaxies: individual: NGC 4151 - galaxies: Seyfert - X-rays: galaxies
Simbad objects: 4
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