{
  "id": "2102.07065",
  "version": "v1",
  "published": "2021-02-14T04:08:28.000Z",
  "updated": "2021-02-14T04:08:28.000Z",
  "title": "The Wolf-Rayet + Black Hole Binary NGC 300 X-1: What is the Mass of the Black Hole?",
  "authors": [
    "Breanna A. Binder",
    "Janelle M. Sy",
    "Michael Eracleous",
    "Dimitris M. Christodoulou",
    "Sayantan Bhattacharya",
    "Rigel Cappallo",
    "Silas Laycock",
    "Paul P. Plucinsky",
    "Benjamin F. Williams"
  ],
  "comment": "Accepted to ApJ. 22 pages, 16 figures, 7 tables",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We present new X-ray and UV observations of the Wolf-Rayet + black hole binary system NGC 300 X-1 with the Chandra X-ray Observatory and the Hubble Space Telescope Cosmic Origins Spectrograph. When combined with archival X-ray observations, our X-ray and UV observations sample the entire binary orbit, providing clues to the system geometry and interaction between the black hole accretion disk and the donor star wind. We measure a binary orbital period of 32.7921$\\pm$0.0003 hr, in agreement with previous studies, and perform phase-resolved spectroscopy using the X-ray data. The X-ray light curve reveals a deep eclipse, consistent with inclination angles of $i=60-75^{\\circ}$, and a pre-eclipse excess consistent with an accretion stream impacting the disk edge. We further measure radial velocity variations for several prominent FUV spectral lines, most notably He II $\\lambda$1640 and C IV $\\lambda$1550. We find that the He II emission lines systematically lag the expected Wolf-Rayet star orbital motion by a phase difference $\\Delta \\phi\\sim0.3$, while C IV $\\lambda$1550 matches the phase of the anticipated radial velocity curve of the Wolf-Rayet donor. We assume the C IV $\\lambda$1550 emission line follows a sinusoidal radial velocity curve (semi-amplitude = 250 km s$^{-1}$) and infer a BH mass of 17$\\pm$4 M$_{\\odot}$. Our observations are consistent with the presence of a wind-Roche lobe overflow accretion disk, where an accretion stream forms from gravitationally focused wind material and impacts the edge of the black hole accretion disk.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-02-14T04:08:28.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "black hole binary ngc",
      "black hole accretion disk",
      "wolf-rayet star orbital motion",
      "telescope cosmic origins spectrograph",
      "lobe overflow accretion disk"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 22,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}