{
  "id": "2202.07072",
  "version": "v1",
  "published": "2022-02-11T18:02:16.000Z",
  "updated": "2022-02-11T18:02:16.000Z",
  "title": "X-ray irradiation of the stellar wind in HMXBs with B supergiants: Implications for ULXs",
  "authors": [
    "J. Krticka",
    "J. Kubat",
    "I. Krtickova"
  ],
  "comment": "11 pages, accepted for publication in Astronomy & Astrophysics",
  "categories": [
    "astro-ph.HE",
    "astro-ph.SR"
  ],
  "abstract": "Wind-fed high-mass X-ray binaries are powered by accretion of the radiatively driven wind on the compact star. Accretion-generated X-rays alter the ionization state of the wind. Because higher ionization states drive the wind less effectively, X-ray ionization may brake acceleration of the wind. This causes a decrease in the wind terminal velocity and mass flux in the direction toward the X-ray source. We study the effect of X-ray ionization on the stellar wind of B supergiants. We determine the binary parameters for which the X-ray irradiation significantly influences the stellar wind. This can be studied in diagrams that plot the optical depth parameter versus the X-ray luminosity. For low optical depths or for high X-ray luminosities, X-ray ionization leads to a disruption in the wind aimed toward the X-ray source. Observational parameters of high-mass X-ray binaries with B-supergiant components appear outside the wind disruption zone. The X-ray feedback determines the resulting X-ray luminosity. For low X-ray luminosities, ionization is weak, and the wind is not disrupted by X-rays and flows at large velocities, consequently the accretion rate is relatively low. On the other hand, for high X-ray luminosities, the X-ray ionization disrupts the flow braking the acceleration, the wind velocity is low, and the accretion rate becomes high. These effects determine the X-ray luminosity of individual binaries. Accounting for the X-ray feedback, estimated X-ray luminosities reasonably agree with observational values. We study the effect of small-scale wind inhomogeneities, showing that they weaken the effect of X-ray ionization by increasing recombination and the mass-loss. This effect is particularly important in the region of the bistability jump. We show that ultraluminous X-ray binaries with $L_x<10^{40}$ erg/s may be powered by accretion of a B-supergiant wind on a massive black hole.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2022-02-11T18:02:16.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "x-ray luminosity",
      "stellar wind",
      "x-ray ionization",
      "x-ray irradiation",
      "x-ray luminosities reasonably agree"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 11,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}