{
  "id": "2309.15141",
  "version": "v1",
  "published": "2023-09-26T18:00:00.000Z",
  "updated": "2023-09-26T18:00:00.000Z",
  "title": "Anisotropic Energy Injection from Magnetar Central Engines in Short GRBs",
  "authors": [
    "Yihan Wang",
    "Bing Zhang",
    "Zhaohuan Zhu"
  ],
  "comment": "Submitted to MNRAS; Comments are welcome",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "A long-lived magnetar, potentially originating from a binary neutron star system, has been proposed to explain the extended emission observed in certain short-duration gamma-ray bursts (sGRBs), and is posited as a potential central engine to power the engine-fed kilonovae. Previously, the process by which energy is injected into the surrounding ejecta/jet was widely believed to be nearly isotropic. In this study, we employ special relativity magnetohydrodynamic (SRMHD) simulations to investigate the wind injection process from a magnetar central engine. We explore the dynamics and energy distribution within the system and found that the parameter $\\alpha=u_{\\rm A}/u_{\\rm MWN}$ can be used to indicate the collimation of the magnetar wind energy injection, where $u_{\\rm A}$ is the local Alfven four-speed and $u_{\\rm MWN}$ is the four-speed of the magnetar wind nebular (MWN) formed from wind-ejecta collision. A significant portion of the injected energy from the magnetar spin-down wind will be channeled to the jet axis due to collimation within the MWN. Achieving isotropic energy injection requires a significantly small $\\alpha$ that necessitates either an ultra-relativistic expanding MWN or an extremely low magnetization MWN, both of which are challenging to attain in sGRBs. Consequently, a considerably reduced energy budget (by a factor of up to 10) is anticipated to be injected into the ejecta for engine-fed kilonovae. Engine-fed kilonovae would appear fainter than originally anticipated.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-09-26T18:00:00.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "magnetar central engine",
      "anisotropic energy injection",
      "short grbs",
      "engine-fed kilonovae",
      "binary neutron star system"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}