X-ray photoionized plasma diagnostics with helium-like ions. Application to warm absorber-emitter in active galactic nuclei

Abstract

Abstract. We present He-like line ratios (resonance, intercombination and forbidden lines) for totally and partially photoionized media. For solar plasmas, these line ratios are already widely used for density and temperature diagnostics of coronal (collisional) plasmas. In the case of totally and partially photoionized plasmas, He-like line ratios allow for the determination of the ionization processes involved in the plasma (photoionization with or without an additional collisional ionization process), as well as the density and the electronic temperature.With the new generation of X-ray satellites, Chandra/AXAF, XMM and Astro-E, it will be feasible to obtain both high spectral resolution and high sensitivity observations. Thus in the coming years, the ratios of these three components will be measurable for a large number of non-solar objects.In particular, these ratios could be applied to the Warm Absorber-Emitter, commonly present in Active Galactic Nuclei (AGN). A better understanding of the Warm Absorber connection to other regions (Broad Line Region, Narrow Line Region) in AGN (Seyferts type-1 and type-2, low-and high-redshift quasars...) will be an important key to obtaining strong constraints on unified schemes.We have calculated He-like line ratios, for Z = 6, 7, 8, 10, 12 and 14, taking into account the upper level radiative cascades which we have computed for radiative and dielectronic recombinations and collisional excitation. The atomic data are tabulated over a wide range of temperatures in order to be used for interpreting a large variety of astrophysical plasmas.

Spatially resolved Fe K spectroscopy of NGC 4945

“…Only the reflected spectrum, arising from the illuminated face of the cloud, has been taken into account in our model. We also produced tables with different densities (ne = 10 3 − 10 4 cm −3 ): all the fits in this paper resulted insensitive to this parameter, as expected since we are always treating density regimes where line ratios of He-like triplets are insensitive to density (Bautista & Kallman 2000;Porquet & Dubau 2000). When this model is applied to the spectra extracted from Region 1 we find log U = 2.2 +0.3 −0.2 , log NH > 23.5 and AF e > 3 with no significant variations to the neutral Fe Kα parameters found in Sect.…”

“…In particular, the ratio of the He-like Fe triplet lines (forbidden, intercombination and resonant) can tell us about the state of the emitting gas. In a photoionized gas, emission from the resonant r iron line is weak, while the forbidden f and the intercombination i lines contribute almost equally to the total emission, considering a wide range of densities (Porquet & Dubau 2000;Bautista & Kallman 2000). On the other hand, in a collisionally ionized gas, the ratio of the lines points in favor of a dominant resonant line, with respect to the forbidden and intercombination lines, such as the case of NGC 6240 (Boller et al 2003;Wang et al 2014).…”

From ultraluminous X-ray sources to ultraluminous supersoft sources: NGC 55 ULX, the missing link

“…An O vii forbidden line (22.1Å) stronger than the resonant line (21.6Å) is a clear indication of photoionization (e.g. Porquet and Dubau 2000). The high ionization ions, e.g.…”

A comprehensive approach to analyzing theXMM-Newtondata of Seyfert 1 galaxies

“…For the Ovii triplet we find energies of about 0.5669, 0.5615, and 0.5539 keV (21.9, 22.1, and 22.4 Å; unconstrained values), implying a velocity of about 3700 km s −1 (z ∼ 0.012). The flux errors in the Ovii lines do not allow us to obtain the coefficients that are commonly used to estimate the density and temperature of the emitting gas (Gabriel & Jordan 1969;Porquet & Dubau 2000). The Oviii line is located at a central energy of 0.652 +0.004 −0.005 keV (∼19 Å), which is compatible with being at the rest frame of Mrk 110.…”