{
  "id": "1701.07338",
  "version": "v1",
  "published": "2017-01-25T14:43:21.000Z",
  "updated": "2017-01-25T14:43:21.000Z",
  "title": "The effect of the atmospheric refractive index on the radio signal of extensive air showers",
  "authors": [
    "A. Corstanje",
    "A. Bonardi",
    "S. Buitink",
    "H. Falcke",
    "J. R. Hörandel",
    "P. Mitra",
    "K. Mulrey",
    "A. Nelles",
    "J. P. Rachen",
    "L. Rossetto",
    "P. Schellart",
    "O. Scholten",
    "S. ter Veen",
    "S. Thoudam",
    "G. Trinh",
    "T. Winchen"
  ],
  "comment": "13 pages, 5 figures. Accepted for publication in Astroparticle Physics",
  "categories": [
    "astro-ph.HE",
    "astro-ph.IM"
  ],
  "abstract": "For the interpretation of measurements of radio emission from extensive air showers, an important systematic uncertainty arises from natural variations of the atmospheric refractive index $n$. At a given altitude, the refractivity $N=10^6\\, (n-1)$ can have relative variations on the order of $10 \\%$ depending on temperature, humidity, and air pressure. Typical corrections to be applied to $N$ are about $4\\%$. Using CoREAS simulations of radio emission from air showers, we have evaluated the effect of varying $N$ on measurements of the depth of shower maximum $X_{\\rm max}$. For an observation band of 30 to 80 MHz, a difference of $4 \\%$ in refractivity gives rise to a systematic error in the inferred $X_{\\rm max}$ between 3.5 and 11 $\\mathrm{g/cm^2}$, for proton showers with zenith angles ranging from 15 to 50 degrees. At higher frequencies, from 120 to 250 MHz, the offset ranges from 10 to 22 $\\mathrm{g/cm^2}$. These offsets were found to be proportional to the geometric distance to $X_{\\rm max}$. We have compared the results to a simple model based on the Cherenkov angle. For the 120 to 250 MHz band, the model is in qualitative agreement with the simulations. In typical circumstances, we find a slight decrease in $X_{\\rm max}$ compared to the default refractivity treatment in CoREAS. While this is within commonly treated systematic uncertainties, accounting for it explicitly improves the accuracy of $X_{\\rm max}$ measurements.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-01-25T14:43:21.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "extensive air showers",
      "atmospheric refractive index",
      "radio signal",
      "important systematic uncertainty arises",
      "radio emission"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 13,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}