X-ray photoionized plasma diagnostics with Helium-like ions. Application to Warm Absorber-Emitter in Active Galactic Nuclei

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.Comment: 23 pages, 11 figures, 14 tables. A&AS, in pres

He-like ions as practical astrophysical plasma diagnostics: From stellar coronae to active galactic nuclei

We review X-ray plasma diagnostics based on the line ratios of He-like ions. Triplet/singlet line intensities can be used to determine electronic temperature and density, and were first developed for the study of the solar corona. Since the launches of the X-ray satellites Chandra and XMM-Newton, these diagnostics have been extended and used (from CV to Si XIII) for a wide variety of astrophysical plasmas such as stellar coronae, supernova remnants, solar system objects, active galactic nuclei, and X-ray binaries. Moreover, the intensities of He-like ions can be used to determine the ionization process(es) at work, as well as the distance between the X-ray plasma and the UV emission source for example in hot stars. In the near future thanks to the next generation of X-ray satellites (e.g., Astro-H and IXO), higher-Z He-like lines (e.g., iron) will be resolved, allowing plasmas with higher temperatures and densities to be probed. Moreover, the so-called satellite lines that are formed closed to parent He-like lines, will provide additional valuable diagnostics to determine electronic temperature, ionic fraction, departure from ionization equilibrium and/or from Maxwellian electron distribution.Comment: 36 pages, 16 figures. Invited Review talk at the "High-resolution X-ray spectroscopy: past, present, and future" conference, Utrecht, March 15-17 2010. Accepted for publication in Space Science Reviews (2010); the final publication is available at http://www.springerlink.co

Absorption spectra of Fe L-lines in Seyfert 1 galaxies

Absorption L-lines of iron ions are observed, in absorption, in spectra of Seyfert 1 galaxies by the new generation of X-ray satellites: Chandra (NASA) and XMM-Newton (ESA). Lines associated to Fe23+ to Fe17+ are well resolved. Whereas, those corresponding to Fe16+ to Fe6+ are unresolved. Forbidden transitions of the Fe16+ to Fe6+ ions were previously observed, for the same objects, in the visible and infra-red regions, showing that the plasma had a low density. To interpret X-ray, visible and infra-red data, astrophysical models assume an extended absorbing medium of very low density surrounding an intense X-ray source. We have calculated atomic data (wavelengths, radiative and autoionization rates) for n=2 to n'=3-4 transitions and used them to construct refined synthetic spectra of the unresolved part of the L-line spectra.Comment: 17 pages, 5 figures, Journal of Quantitative Spectroscopy and Radiative Transfer, in pres

Characteristics of Solar Flare Doppler Shift Oscillations Observed with the Bragg Crystal Spectrometer on Yohkoh

This paper reports the results of a survey of Doppler shift oscillations measured during solar flares in emission lines of S XV and Ca XIX with the Bragg Crystal Spectrometer (BCS) on Yohkoh. Data from 20 flares that show oscillatory behavior in the measured Doppler shifts have been fitted to determine the properties of the oscillations. Results from both BCS channels show average oscillation periods of 5.5 +/- 2.7 minutes, decay times of 5.0 +/-2.5 minutes, amplitudes of 17.1 +/- 17.0 km/s, and inferred displacements of 1070 +/- 1710 km, where the listed errors are the standard deviations of the sample means. For some of the flares, intensity fluctuations are also observed. These lag the Doppler shift oscillations by 1/4 period, strongly suggesting that the oscillations are standing slow mode waves. The relationship between the oscillation period and the decay time is consistent with conductive damping of the oscillations.Comment: Accepted for publication in Ap

Highly Ionized Potassium Lines in Solar X-ray Spectra and the Abundance of Potassium

The abundance of potassium is derived from X-ray lines observed during flares by the RESIK instrument on the solar mission CORONAS-F between 3.53 A and 3.57 A. The lines include those emitted by He-like K and Li-like K dielectronic satellites, which have been synthesized using the CHIANTI atomic code and newly calculated atomic data. There is good agreement of observed and synthesized spectra, and the theoretical behavior of the spectra with varying temperature estimated from the ratio of the two GOES channels is correctly predicted. The observed fluxes of the He-like K resonance line per unit emission measure gives log A(K) = 5.86 (on a scale log A(H) = 12), with a total range of a factor 2.9. This is higher than photospheric abundance estimates by a factor 5.5, a slightly greater enhancement than for other elements with first ionization potential (FIP) less than about 10 eV. There is, then, the possibility that enrichment of low-FIP elements in coronal plasmas depends weakly on the value of the FIP which for K is extremely low (4.34 eV). Our work also suggests that fractionation of elements to form the FIP effect occurs in the low chromosphere rather than higher up, as in some models.Comment: 14 pages, 3 figure

X-ray Line Diagnostics of Hot Accretion Flows around Black Holes

We compute X-ray emission lines from thermal plasma in hot accretion flows. We show that line profiles are strong probes of the gas dynamics, and we present line-ratio diagnostics which are sensitive to the distribution of mass with temperature in the flow. We show how these can be used to constrain the run of density with radius, and the size of the hot region. We also present diagnostics which are primarily sensitive to the importance of recombination versus collisional ionization, and which could help discriminate ADAFs from photoionization-dominated accretion disk coronae. We apply our results to the Galactic center source Sagittarius A* and to the nucleus of M87. We find that the brightest predicted lines are within the detection capability of current $X$-ray instruments.Comment: 16 pages, 1 table, 9 figures, accepted to Ap

RESIK observations of He-like Ar X-ray line emission in solar flares

The Ar XVII X-ray line group principally due to transitions 1s2 - 1s2l (l=s, p) near 4 Anstroms was observed in numerous flares by the RESIK bent crystal spectrometer aboard CORONAS-F between 2001 and 2003. The three line features include the Ar XVII w (resonance line), a blend of x and y (intercombination lines), and z (forbidden line), all of which are blended with Ar XVI dielectronic satellites. The ratio G, equal to [I(x+y) + I(z)]/I(w), varies with electron temperature Te mostly because of unresolved dielectronic satellites. With temperatures estimated from GOES X-ray emission, the observed G ratios agree fairly well with those calculated from CHIANTI and other data. With a two-component emission measure, better agreement is achieved. Some S XV and S XVI lines blend with the Ar lines, the effect of which occurs at temperatures greater than 8MK, allowing the S/Ar abundance ratio to be determined. This is found to agree with coronal values. A nonthermal contribution is indicated for some spectra in the repeating-pulse flare of 2003 February 6.Comment: Latex file and 3 ps files. Astrophysical Journal Letters (accepted, June 2008