@article{fba570f32b3d4fd996bd420340970eac,
title = "Broad Non-Gaussian Fe xxiv Line Profiles in the Impulsive Phase of the 2017 September 10 X8.3-class Flare Observed by Hinode/EIS",
abstract = "We analyze the spectra of high-temperature Fe xxiv lines observed by the Hinode/Extreme-Ultraviolet Imaging Spectrometer (EIS) during the impulsive phase of the X8.3-class flare on 2017 September 10. The line profiles are broad, show pronounced wings, and clearly depart from a single-Gaussian shape. The lines can be well fitted with κ distributions, with values of κ varying between ≈1.7 and 3. The regions where we observe the non-Gaussian profiles coincide with the location of high-energy (≈100-300 keV) hard X-ray (HXR) sources observed by RHESSI, suggesting the presence of particle acceleration or turbulence, also confirmed by the observations of nonthermal microwave sources with the Expanded Owens Valley Solar Array at and above the HXR loop-top source. We also investigate the effect of taking into account κ distributions in the temperature diagnostics based on the ratio of the Fe xxiii λ263.76 and Fe xxiv λ255.1 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. Although larger line widths are expected because of these higher formation temperatures, the observed line widths still imply nonthermal broadening in excess of 200 km s-1. The nonthermal broadening related to HXR emission is better interpreted by turbulence than by chromospheric evaporation.",
keywords = "Sun: UV radiation, Sun: activity, Sun: flares, line: profiles, radiation mechanisms: nonthermal, techniques: spectroscopic",
author = "Vanessa Polito and Jaroslav Dudik and Jana Ka{\v s}parov{\'a} and Elena Dzif{\v c}{\'a}kov{\'a} and Reeves, {Katharine K.} and Paola Testa and Bin Chen",
note = "Funding Information: The authors acknowledge helpful discussions with M. Karlick{\'y}, G. Del Zanna, and H. E. Mason. J.K. would like to thank the RHESSI team, namely, K. Tolbert, B. Dennis, S. Krucker, and R. Schwartz, for their invaluable advice and software support. V.P. is supported by NASA grant NNX15AF50G, grant no. 2015-065 from the University of Alabama in Huntsville, and contract 8100002705 from Lock-heed-Martin to SAO. P.T. acknowledges support by NASA grant NNX15AF50G, contract 8100002705 from Lockheed-Martin to SAO, and contract NNM07AB07C to SAO. Funding Information: J.D., J.K., and E.D. acknowledge support from grant nos. 17-16447S and 18-09072S of the Grant Agency of the Czech Republic, as well as institutional support RVO:67985815 from the Czech Academy of Sciences. B.C. acknowledges support by NASA grant NNX17AB82G and NSF grant AGS-1654382. V.P., J.K., and K.K.R. would like to thank the International Space Science Institute (ISSI) for their support and hospitality during the meetings of the ISSI Bern-Beijing team on “Diagnosing heating mechanisms in solar flares through spectroscopic observations of flare ribbons.” AIA data are courtesy of NASA/SDO and the AIA science team. Hinode is a Japanese mission developed and launched by ISAS/JAXA, with NAOJ as domestic partner and NASA and STFC (UK) as international partners. It is operated by these agencies in cooperation with ESA and NSC (Norway). CHIANTI is a collaborative project involving the NRL (USA), the University of Cambridge (UK), and George Mason University (USA). Facilities: Hinode, SDO, RHESSI, EOVSA. Publisher Copyright: {\textcopyright} 2018. The American Astronomical Society. All rights reserved..",
year = "2018",
month = sep,
day = "1",
doi = "10.3847/1538-4357/aad62d",
language = "English (US)",
volume = "864",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "1",
}