{
  "id": "2105.12853",
  "version": "v1",
  "published": "2021-05-26T21:23:42.000Z",
  "updated": "2021-05-26T21:23:42.000Z",
  "title": "He I spectropolarimetry of a supersonic coronal downflow within a sunspot umbra",
  "authors": [
    "Thomas A. Schad",
    "Gabriel I. Dima",
    "Tetsu Anan"
  ],
  "comment": "Accepted for publication in ApJ",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "We report spectropolarimetric observations of a supersonic downflow impacting the lower atmosphere within a large sunspot umbra. This work is an extension of Schad et al. 2016 using observations acquired in the He I 10830 Angstrom triplet by the Facility Infrared Spectropolarimeter. Downflowing material accelerating along a cooled coronal loop reaches peak speeds near 200 km s$^{-1}$ and exhibits both high speed emission and absorption within the umbra, which we determine to be a consequence of the strong height dependence of the radiatively-controlled source function above the sunspot umbra. Strong emission profiles close to the rest wavelengths but with long red-shifted tails are also observed at the downflow terminus. From the polarized spectra, we infer longitudinal magnetic field strengths of ${\\sim}2.4$ kG in the core portion of the He I strong emission, which we believe is the strongest ever reported in this line. Photospheric field strengths along the same line-of-sight are ${\\sim}2.8$ kG as inferred using the Ca I 10839 Angstrom spectral line. The temperatures of the highest speed He I absorption and the near rest emission are similar (${\\sim}$10 kK), while a differential emission measure analysis using SDO/AIA data indicates significant increases in radiative cooling for temperatures between $\\sim$0.5 and 1 MK plasma associated with the downflow terminus. Combined we interpret these observations in the context of a strong radiative shock induced by the supersonic downflow impacting the low sunspot atmosphere.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-05-26T21:23:42.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "sunspot umbra",
      "supersonic coronal downflow",
      "infer longitudinal magnetic field strengths",
      "coronal loop reaches peak speeds",
      "strong emission"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}