Broad Non-Gaussian Fe XXIV Line Profiles in the Impulsive Phase of the 2017 September 10 X8.3 class Flare Observed by Hinode/EIS

In this work, we analyze the spectra of high temperature Fe XXIV lines observed by Hinode/EIS during the impulsive phase of the X8.3 class flare on September 10, 2017. The line profiles are broad, show pronounced wings, and clearly depart from a single Gaussian shape. The lines can be well fitted with kappa distributions, with values of kappa varying between~1.7 to 3. The regions where we observe the non-Gaussian profiles coincide with the location of high-energy ~100-300 keV) HXR sources observed by RHESSI, suggesting the presence of particle acceleration or turbulence, also confirmed by the observations of a non-thermal microwave sources with the EOVSA at and above the HXR looptop source. We also investigate the effect of taking into account $\kappa$ distributions in the temperature diagnostics based on the ratio of the Fe XXIII 263.76A Fe XXIV 255.1A EIS lines. We found that these lines can be formed at much higher temperatures than expected (up to log(t[K])~7.8), if departures from Maxwellian distributions are taken into account.