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

We analyze the spectra of high temperature fexxiv~lines observed by emph{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~$approx$1.7 to 3. The regions where we observe the non-Gaussian profiles coincide with the location of high-energy ($approx$100--300 keV) HXR sources observed by emph{RHESSI}, suggesting the presence of particle acceleration or turbulence, also confirmed by the observations of a non-thermal microwave sources with the emph{Expanded Owens Valley Solar Array} (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 fexxiii~263.76~AA~and fexxiv~255.1~AA~EIS lines. We found that these lines can be formed at much higher temperatures than expected (up to log($T$,[K]),$approx$,7.8), if departures from Maxwellian distributions are taken into account. Although larger line widths are expected because of these higher formation temperatures, the observed line widths still imply non-thermal broadening in excess of ~200,kps. The non-thermal broadening related to HXR emission is better interpreted by turbulence rather than chromospheric evaporation.