{
  "id": "1805.12285",
  "version": "v1",
  "published": "2018-05-31T01:54:22.000Z",
  "updated": "2018-05-31T01:54:22.000Z",
  "title": "The Multi-Instrument (EVE-RHESSI) DEM for Solar Flares, and Implications for Non-Thermal Emission",
  "authors": [
    "James M. McTiernan",
    "Amir Caspi",
    "Harry P. Warren"
  ],
  "comment": "10 pages, 12 figures, 2 tables; accepted for publication in Astrophysical Journal",
  "categories": [
    "astro-ph.SR",
    "astro-ph.HE",
    "astro-ph.IM",
    "physics.plasm-ph",
    "physics.space-ph"
  ],
  "abstract": "Solar flare X-ray spectra are typically dominated by thermal bremsstrahlung emission in the soft X-ray ($\\lesssim$10 keV) energy range; for hard X-ray energies ($\\gtrsim$30 keV), emission is typically non-thermal from beams of electrons. The low-energy extent of non-thermal emission has only been loosely quantified. It has been difficult to obtain a lower limit for a possible non-thermal cutoff energy due to the significantly dominant thermal emission. Here we use solar flare data from the EUV Variability Experiment (EVE) on-board the Solar Dynamics Observatory (SDO) and X-ray data from the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) to calculate the Differential Emission Measure (DEM). This improvement over the isothermal approximation and any single-instrument DEM helps to resolve ambiguities in the range where thermal and non-thermal emission overlap, and to provide constraints on the low-energy cutoff. In the model, thermal emission is from a DEM that is parametrized as multiple gaussians in $Log(T)$. Non-thermal emission results from a photon spectrum obtained using a thick-target emission model. Spectra for both instruments are fit simultaneously in a self-consistent manner. Our results have been obtained using a sample of 52 large (GOES X- and M-class) solar flares observed between February 2011 and February 2013. It turns out that it is often possible to determine low-energy cutoffs early (in the first two minutes) during large flares. Cutoff energies are typically low, less than 10 keV, with most values of the lower limits in the 5--7 keV range.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-05-31T01:54:22.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "non-thermal emission",
      "solar flare",
      "reuven ramaty high energy spectroscopic",
      "ramaty high energy spectroscopic imager",
      "multi-instrument"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 10,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}