{
  "id": "2110.15392",
  "version": "v1",
  "published": "2021-10-28T18:31:07.000Z",
  "updated": "2021-10-28T18:31:07.000Z",
  "title": "On the torque reversals of 4U 1626--67",
  "authors": [
    "Ali Arda Gencali",
    "Ndiogou Niang",
    "Ozan Toyran",
    "Unal Ertan",
    "Ayse Ulubay",
    "Sinem Sasmaz",
    "Ebru Devlen",
    "Armin Vahdat",
    "Seyda Ozcan",
    "M. Ali Alpar"
  ],
  "comment": "5 pages, 2 figures, accepted for publication in A&A",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We have investigated the detailed torque-reversal behavior of 4U 1626--67 in the framework of the recently developed comprehensive model of the inner disk radius and torque calculations for neutron stars accreting from geometrically thin disks. The model can reproduce the torque -- X-ray luminosity relation across the torque reversals of 4U 1626--67. Our results imply that: (1) rotational equilibrium is reached when the inner disk radius equals the co-rotation radius, $r_\\mathrm{co}$, while the conventional Alfven radius is greater than and close to $r_\\mathrm{co}$, (2) both spin-up and spin-down torques are operating on either side of torque reversal, (3) with increasing accretion rate the spin-up torque associated with accretion onto the star gradually dominates the spin-down torque exerted by the disk. The torque reversals are the natural outcome of transitions between the well-defined weak-propeller and spin-up phases of the star with a stable geometrically thin accretion disk.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-10-28T18:31:07.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "torque reversal",
      "spin-down torque",
      "inner disk radius equals",
      "x-ray luminosity relation",
      "conventional alfven radius"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 5,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}