Diagnostics of the non-Maxwellian-distributions from Fe XVII–XVIII X-ray coronal spectra: proposal for the Marshall Grazing-Incidence X-ray Spectrometer (MaGIXS)

Kappa-distributions belong to the family of non-Maxwellian distributions with the Maxwellian core and a power law high-energy tail. Their presence in the solar corona can originate in impulsive coronal heating or turbulence. Therefore, their spectroscopic diagnostics represents an important imput for our understanding of physical processes in solar corona. For that reason, effects of kappa-distributions on X-ray line intensities to be observed by the upcoming Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) were analyzed. Synthetic Fe XVII–Fe XVIII spectra in the 6 - 24 A spectral range were calculated for wide ranges of temperatures, electron densities and kappa values and used to propose the diagnostics of the kappa-distributions. The combinations of a ratio involving both Fe xvii and Fe xviii line with another ratio involving lines formed within a single ion provide the best diagnostic options with the sensitivity a few tens of per cent of the line ratio. Much higher sensitivity, of about a factor of 2–3, was found for the combination of the X-ray lines with the Fe XVIII 93.93 Å line observed by SDO/AIA. We can conclude that the MaGIXS instrument has a good opportunity to diagnose departures of electron distribution from the Maxwellian distribution, especially in active region cores.