{
  "id": "1703.05336",
  "version": "v1",
  "published": "2017-03-15T18:01:11.000Z",
  "updated": "2017-03-15T18:01:11.000Z",
  "title": "Narrow phase-dependent features in X-ray Dim Isolated Neutron Stars: a new detection and upper limits",
  "authors": [
    "A. Borghese",
    "N. Rea",
    "F. Coti Zelati",
    "A. Tiengo",
    "R. Turolla",
    "S. Zane"
  ],
  "comment": "10 pages, 5 figures, 4 tables. Accepted for publication in MNRAS",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We report on the results of a detailed phase-resolved spectroscopy of archival XMM--Newton observations of X-ray Dim Isolated Neutron Stars (XDINSs). Our analysis revealed a narrow and phase-variable absorption feature in the X-ray spectrum of RX J1308.6+2127. The feature has an energy of $\\sim$740 eV and an equivalent width of $\\sim$15 eV. It is detected only in $\\sim$ 1/5 of the phase cycle, and appears to be present for the entire timespan covered by the observations (2001 December - 2007 June). The strong dependence on the pulsar rotation and the narrow width suggest that the feature is likely due to resonant cyclotron absorption/scattering in a confined high-B structure close to the stellar surface. Assuming a proton cyclotron line, the magnetic field strength in the loop is B$_{loop} \\sim 1.7 \\times 10^{14}$ G, about a factor of $\\sim$5 higher than the surface dipolar magnetic field (B$_{surf} \\sim 3.4 \\times 10^{13}$ G). This feature is similar to that recently detected in another XDINS, RX J0720.4-3125, showing (as expected by theoretical simulations) that small scale magnetic loops close to the surface might be common to many highly magnetic neutron stars (although difficult to detect with current X-ray instruments). Furthermore, we investigated the available XMM--Newton, data of all XDINSs in search for similar narrow phase-dependent features, but could derive only upper limits for all the other sources.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-03-15T18:01:11.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "x-ray dim isolated neutron stars",
      "narrow phase-dependent features",
      "upper limits",
      "small scale magnetic loops close"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 10,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}