Signatures of the non-Maxwellian κ-distributions in optically thin line spectra

Abstract

Aims. We investigate the possibility of diagnosing the degree of departure from the Maxwellian distribution using single-ion spectra originating in astrophysical plasmas in collisional ionization equilibrium. Methods. New atomic data for excitation of Fe ix -Fe xiii are integrated under the assumption of a κ-distribution of electron energies. Diagnostic methods using lines of a single ion formed at any wavelength are explored. Such methods minimize uncertainties from the ionization and recombination rates, as well as the possible presence of non-equilibrium ionization. Approximations to the collision strengths are also investigated. Results. The calculated intensities of most of the Fe ix -Fe xiii EUV lines show consistent behaviour with κ at constant temperature. Intensities of these lines decrease with κ, with the vast majority of ratios of strong lines showing little or no sensitivity to κ. Several of the line ratios, especially involving temperature-sensitive lines, show a sensitivity to κ that is of the order of several tens of per cent, or, in the case of Fe ix, up to a factor of two. Forbidden lines in the near-ultraviolet, visible, or infrared parts of the spectrum are an exception, with smaller intensity changes or even a reverse behaviour with κ. The most conspicuous example is the Fe x 6378.26Å red line, whose intensity incerases with κ. This line is a potentially strong indicator of departures from the Maxwellian distribution. We find that it is possible to perform density diagnostics independently of κ, with many Fe xi, Fe xii, and Fe xiii line ratios showing strong density-sensitivity and negligible sensitivity to κ and temperature. We also tested different averaging of the collision strengths. It is found that averaging over 0.01 interval in log(E[Ryd]) is sufficient to produce accurate distribution-averaged collision strengths Υ(T, κ) at temperatures of the ion formation in ionization equilibrium.

Plasma Diagnostics from Active Region and Quiet-Sun Spectra Observed by Hinode/EIS: Quantifying the Departures from a Maxwellian Distribution

“…Of these, the T and κ are parameters of the distribution (Equation 1), and must be diagnosed simultaneously. The line ratios sensitive to κ are also a function of electron density (Dzifčáková & Kulinová 2010;Mackovjak et al 2013;Dudík et al 2014Dudík et al , 2015Dudík et al , 2019Dzifčáková et al 2018). Therefore, the electron density N e is diagnosed prior to diagnostics of T and κ.…”

“…Theoretical combinations of line ratios sensitive to κ observed by the Extreme-ultraviolet and Imaging Spectrometer (EIS; Culhane et al 2007) onboard the Hinode satellite (Kosugi et al 2007) were investigated by Dzifčáková & Kulinová (2010) and Dudík et al (2014Dudík et al ( , 2019. In all cases, one line in a ratio sensitive to κ is observed in the shortwavelength and the other in the long-wavelength channel.…”

The First Flight of the Marshall Grazing Incidence X-Ray Spectrometer (MaGIXS)

“…Quantifying the number of high-energy particles provides strong constraints on the possible coronal heating mechanisms, with the presence of non-Maxwellian distributions clearly indicating nanoflare heating. The potential of the MaGIXS instrument in this respect is discussed in Dudik et al (2019).…”

High Resolution Soft X-ray Spectroscopy and the Quest for the Hot (5–10 MK) Plasma in Solar Active Regions

“…The X-rays are excellent for measuring the chemical abundances of hot plasma. They also allow estimates of nonthermal electrons via line ratio techniques (Dudík et al, 2019), although better diagnostics are available at shorter wavelengths, involving satellite lines (see e.g., the review by Del Zanna and Mason, 2018). The X-rays also provide electron density diagnostics but for the hot (10 MK) lines they are limited to high values (above 10 12 cm −3 ).…”