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We analyze the spectra of high temperature \fexxiv~lines observed by\emph{Hinode}/EIS during the impulsive phase of the X8.3--class flare onSeptember 10, 2017. The line profiles are broad, show pronounced wings, andclearly depart from a single Gaussian shape. The lines can be well fitted with$\kappa$ distributions, with values of $\kappa$ varying between~$\approx$1.7 to3. The regions where we observe the non-Gaussian profiles coincide with thelocation of high-energy ($\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 looptopsource. 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 linescan be formed at much higher temperatures than expected (up tolog($T$\,[K])\,$\approx$\,7.8), if departures from Maxwellian distributions aretaken into account. Although larger line widths are expected because of thesehigher formation temperatures, the observed line widths still imply non-thermalbroadening in excess of ~200\,\kps. The non-thermal broadening related to HXRemission is better interpreted by turbulence rather than chromosphericevaporation.

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