{
  "id": "1705.02104",
  "version": "v1",
  "published": "2017-05-05T07:15:59.000Z",
  "updated": "2017-05-05T07:15:59.000Z",
  "title": "Non-Maxwellian analysis of the transition-region line profiles observed by the Interface Region Imaging Spectrograph",
  "authors": [
    "Jaroslav Dudik",
    "Vanessa Polito",
    "Elena Dzifcakova",
    "Giulio Del Zanna",
    "Paola Testa"
  ],
  "comment": "The Astrophysical Journal, accepted",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "We investigate the nature of the spectral line profiles for transition region ions observed with the Interface Region Imaging Spectrograph (IRIS). In this context, we have analyzed an active-region observation performed by IRIS in its 1400 A spectral window. The transition-region lines are found to exhibit significant wings in their spectral profiles, which can be well-fitted with non-Maxwellian kappa-distribution. The fit with a kappa-distribution can perform better than a double Gaussian fit, especially for the strongest line, Si IV 1402.8 A. Typical values of $\\kappa$ found are about 2, occurring in a majority of spatial pixels where the transition region lines are symmetric, i.e., the fit can be performed. Furthermore, all five spectral lines studied (from Si IV, O IV and S IV) appear to have the same FWHM irrespective of whether the line is an allowed or an intercombination transition. A similar value of kappa is obtained for the electron distribution by fitting of the line intensities relative to Si IV 1402.8 A, if photospheric abundances are assumed. The kappa-distributions however do not remove the presence of non-thermal broadening. Instead, they actually increase the non-thermal width. This is because for kappa-distributions the transition-region ions are formed at lower temperatures. The large observed non-thermal width lowers the opacity of the Si IV line sufficiently enough for this line to become optically thin.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-05-05T07:15:59.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "interface region imaging spectrograph",
      "transition-region line profiles",
      "non-maxwellian analysis",
      "non-thermal width",
      "transition region"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}