Astrophysical Line Diagnosis Requires Nonlinear Dynamical Atomic Modeling

Abstract

Line intensities and oscillator strengths for the controversial 3C and 3D astrophysically relevant lines in neonlike Fe 16+ ions are calculated. We show that, for strong x-ray sources, the modeling of the spectral lines by a peak with an area proportional to the oscillator strength is not sufficient and non-linear dynamical effects have to be taken into account. Furthermore, a large-scale configurationinteraction calculation of oscillator strengths is performed with the inclusion of higher-order electroncorrelation effects. The dynamical effects give a possible resolution of discrepancies of theory and experiment found by recent measurements, which motivates the use of light-matter interaction models also valid for strong light fields in the analysis and interpretation of astrophysical and laboratory spectra.PACS numbers: 31.15.am,32.30.Rj,42.50.Ct Astrophysical spectra recorded by space observatories provide the only means to determine the element composition, temperature, density, and velocity of distant celestial objects such as stars, x-ray binaries, black hole accretion discs, or active galactic nuclei [1][2][3][4][5][6][7][8][9]. Such x-ray (or optical) spectra are often composed of a series of peaks associated with a range of elements, ionic charge states, and transitions. Therefore, a large amount of reliable atomic data is needed to disentangle the physical properties of the emitting objects. Such data-transition energies and probabilities, oscillator strengths, collisional and recombination cross sections, etc.-may be obtained from laboratory astrophysics experiments (see e.g. [3, 10-16]) or, more economically, from theoretical calculations (see e.g. [17][18][19][20]).The x-ray emission lines of highly charged Fe ions are among the brightest in astrophysical spectra. Within the last decade, several observations were performed with the space laboratories Chandra and XMM-Newton (see e.g. [5,6,21,22]). The line-strength ratio of two 2p → 3d lines in Fe 16+ , customarily denoted as 3C [2p 6 (J = 0) → (2p 5 ) 1/2 3d 3/2 (J = 1), transition energy of 826 eV] and 3D [2p 6 (J = 0) → (2p 5 ) 3/2 3d 5/2 (J = 1), at 812 eV], was observed, but the results disagreed with theoretical predictions [17][18][19][20]. Initially this disagreement was considered to originate from the co-existence of different charge states of Fe, and later, after laboratory measurements, as an effect of electron-impact excitation of the ion. Furthermore, since several theoretical calculations of transition probabilities in highly charged ions agreed well with the experiments (see, e.g. [23][24][25]), there was no reason to assume that essential contributions had not been included in the predictions. The question was out of focus until the first laser spectroscopic experiment in the x-ray regime [3], enabled by the advent of x-ray freeelectron-laser (XFEL) facilities [26]. This experiment at the Linac Coherent Light Source (LCLS, Ref.[27]) gave hints for an incorrect atomic structure theory: a disagreement between all state-of-the-art ...

Comment on “Theoretical Confirmation of the Low Experimental 3C/3D f -Value Ratio in Fe xvii”

“…Taking fine-tuning and 2p-orbital relaxation into account, MB obtained the ratio fð3CÞ=fð3DÞ ¼ 2.82, in good agreement with the measured ratio 2.61 AE 0.23 [2] and concluded that there is no need to consider nonlinear dynamical modeling [3,4] or nonequilibrium plasma effects [5,6] when interpreting experiments. We argue that the inaccurate energy structure in Ref.…”

X-ray-assisted nuclear excitation by electron capture in optical laser-generated plasmas

“…It is likely that by taking into account the effect of the XFEL coherence properties on photoionization in a similar manner as in Refs. [55,56], these fractions of plasma ions with L-shell holes will increase. In the following, for an order of magnitude estimate of the isomer depletion in the x-ray assisted NEEC in optical-laser-generated plasmas, we will assume that N h iso = N iso .…”

Relativistic opacities for astrophysical applications

“…[6], a difference of 3.6 standard deviations was reported between the measured 3C/3D oscillator strength ratio and state-ofthe-art theoretical calculations, calling into question the validity of fundamental atomic structure calculations. This discrepancy has been largely resolved by using time-dependent rate equations to reinterpret the experimental results as a measured line intensity ratio rather than the more fundamental oscillator strength ratio [8,9]. The second, very recent article concerned the frequencydependent LTE opacity of iron under conditions associated with the base of the solar convection zone [10].…”