{
  "id": "1610.03860",
  "version": "v1",
  "published": "2016-10-12T20:02:07.000Z",
  "updated": "2016-10-12T20:02:07.000Z",
  "title": "X-ray counterpart of gravitational waves due to binary neutron star mergers: light curves, luminosity functions, and event rate densities",
  "authors": [
    "Hui Sun",
    "Bing Zhang",
    "He Gao"
  ],
  "comment": "9 pages, 5 figure, Submitted to ApJ",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "Zhang (2013) proposed a type of GRB-less X-ray transient associated with double neutron star (NS-NS) mergers under the conjecture of a rapidly-spinning magnetar merger product with the line of sight off the short GRB beam. We investigate possible light curves of these transients by considering different observer's viewing angles, including looking into a free zone where the emission due to direct dissipation of the magnetar wind is observable, and a trapped zone where X-rays are initially trapped by the ejecta launched during the merger, but later become transparent when the ejecta become optically thin. We perform Monte Carlo simulations to calculate the peak luminosity function (LF) and event rate density of these X-ray transients. By considering that a fraction of massive neutron stars may be supra-massive and collapse into black holes after a certain time, we investigate how the predicted luminosity functions depend on the equation of state (EoS) of the central object. In general, the luminosity functions can be fit by two log-normal distributions peaking around $10^{46.4}$ and $10^{49.6}$ $\\rm erg\\,s^{-1}$, respectively. The relative amplitude of the two peaks relies on the solid angle ratio of the free and trapped zones. As there is no firm detection of such transients, we place constraints on the free zone solid angle at most a few times of the solid angle of the short gamma-ray burst jet. The event rate density of these X-ray transients is around a few tens of $\\rm Gpc^{-3}yr^{-1}$ for luminosity above $10^{45}$ $\\rm erg\\,s^{-1}$. We predict that future X-ray telescope (such as Einstein Probe) with sensitivity of the order of $10^{-11}$ $\\rm erg\\,s^{-1}\\,cm^{-2}$ would detect as many as several tens of such transients per year per steradian, and about 3 transients per year all sky within 300 Mpc, the aLIGO horizon for NS-NS mergers.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-10-12T20:02:07.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "event rate density",
      "binary neutron star mergers",
      "luminosity function",
      "light curves",
      "x-ray counterpart"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 9,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}