{
  "id": "1812.03465",
  "version": "v1",
  "published": "2018-12-09T11:45:55.000Z",
  "updated": "2018-12-09T11:45:55.000Z",
  "title": "Constraining the Braking Index and Energy Partition of Magnetar spin-down with {\\em Swift}/XRT data",
  "authors": [
    "Hou-Jun Lü",
    "Lin Lan",
    "En-Wei Liang"
  ],
  "comment": "8 pages, 3 figures. Accepted for publication in ApJ",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "Observationally, the long-lasting X-ray plateau emission in long GRBs show evidence for ongoing energy injection which may be from magnetar spin-down due to energy released via magnetic dipole (MD) or gravitational wave (GW) radiation. In this paper, by systematically analyzing the {\\em Swift}/XRT light curves detected before 2018 July, we find 45 light curves that monotonously decay as smooth broken power-law with redshift measured. By assuming that the central engines of these GRBs are a newly-born magnetar, we measure the braking index $n$ of putative millisecond magnetars via MD and GW radiations. The inferred braking indices are neither closed to 3 nor to 5, but range between them with a normal distribution ($n_{\\rm c}=4.02\\pm 0.11$). We define one dimensionless parameter $\\Re$ which is the ratio between MD and GW components, and find that the energy released of magnetar spin-down in most GRBs of our sample are dominated by GW radiation for given $P_0=3$ ms and $\\epsilon=0.005$, 0.01. On the other hand, we find that $\\Re$ and braking index $n$ seem to be following an anti-correlation within a large systematic error at $t=0$, but depended on the parameters of $P_0$ and $\\epsilon$ values. Those results suggest that the contribution of GW radiation can not be ignored and the larger braking index are leading to GW dominated the energy released of magnetar spin-down if indeed magnetars are operating in some long GRBs.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-12-09T11:45:55.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "braking index",
      "magnetar spin-down",
      "energy partition",
      "gw radiation",
      "long grbs"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 8,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}