{
  "id": "2104.04708",
  "version": "v1",
  "published": "2021-04-10T08:24:09.000Z",
  "updated": "2021-04-10T08:24:09.000Z",
  "title": "Fallback Accretion Halted by R-process Heating in Neutron Star Mergers and Gamma-Ray Bursts",
  "authors": [
    "Wataru Ishizaki",
    "Kenta Kiuchi",
    "Kunihito Ioka",
    "Shinya Wanajo"
  ],
  "comment": "16 pages, 13 figures",
  "categories": [
    "astro-ph.HE",
    "astro-ph.SR"
  ],
  "abstract": "The gravitational wave event GW170817 with a macronova/kilonova shows that a merger of two neutron stars ejects matter with radioactivity including $r$-process nucleosynthesis. A part of the ejecta inevitably falls back to the central object, possibly powering long-lasting activities of a short gamma-ray burst (sGRB), such as extended and plateau emissions. We investigate the fallback accretion with the $r$-process heating by performing one-dimensional hydrodynamic simulations and developing a semi-analytical model. We show that the usual fallback rate $dM/dt \\propto t^{-5/3}$ is halted by the heating because pressure gradients accelerate ejecta beyond an escape velocity. The suppression is steeper than Chevalier's power-law model through Bondi accretion within a turn-around radius. The characteristic halting timescale is $\\sim 10^5$--$10^9$ sec for the GW170817-like $r$-process heating, which is long enough to continue the long-lasting emission of sGRBs. The halting timescale is sensitive to the uncertainty of the $r$-process. Future observation of fallback halting could constrain the $r$-process heating on the year scale.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-04-10T08:24:09.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "neutron star mergers",
      "fallback accretion",
      "gamma-ray burst",
      "r-process heating",
      "pressure gradients accelerate ejecta"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 16,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}