HEAD Division Meeting 1999, April 1999
Session 2. AGN
Poster, Monday, April 12, 1999, 8:30am-6:10pm, Gold Room

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[2.04] Absorbers/Emitters in AGN: a High Spectral Resolution Wiew

F. Nicastro, M. Elvis (SAO)

Ionized gas absorbing soft X-ray is present in almost half type 1 AGN. The ionization models considered so far have assumed equilibrium photoelectric absorption as the only relevant process. Until now this was justified since the low energy resolution of X-ray instrumentation only barely allows the separation of the K-edges of the two most abundant ions of the oxygen in highly ionized gas: OVII (0.74 keV) and OVIII (0.87 keV). Using such simplifying assumptions leaves many important astrophysical questions about these ionized absorbers (e.g. what is ionizing the gas, what are the typical electron densities in the clouds, what is the distance of the gas from the central source, how is this component related to the other components known to be in the AGN environment).

We instead present models which account for: (a) time-evolving photoionization; (b) resonant absorption; (c) gas emission (continuum plus lines). We give evidence for non-equilibrium effects, partially collisionally ionized medium, geometrical effetcs (including gas emission from non-absorbed sources).

Thanks to their high energy resolution and medium-to-high collecting area, the new generation of X-ray spectrometers will enable the possibility to really detect both time-evolving effects and emission/absorption narrow spectral features, through the direct measurement of the absorption edge optical depths and of the intensity and equivalent widths of the absorption and emission lines. This will allow us to directly measure many important physical and geometrical quantities of the ionized gas. We show simulations of our models with the AXAF-HETG, XMM-RGS and the baseline Con-X Calorimeter, and discuss the physics which can be addressed.

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