{
  "id": "1705.06638",
  "version": "v1",
  "published": "2017-05-18T15:08:54.000Z",
  "updated": "2017-05-18T15:08:54.000Z",
  "title": "Analysis of NuSTAR and Suzaku observations of Cyg X-1 in the hard state: evidence for a truncated disc geometry",
  "authors": [
    "Rupal Basak",
    "Andrzej A. Zdziarski",
    "Michael Parker",
    "Nazma Islam"
  ],
  "comment": "submitted to MNRAS, comments are welcome",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "The geometry of the accretion flow in black-hole X-ray binaries in the hard state, in particular the position of the disc inner edge, has been a subject of intense debate in recent years. We address this issue by performing a spectral study of simultaneous observations of Cyg X-1 in the hard state by {\\it{NuSTAR}\\} and {\\it{Suzaku}}. The same data were analysed before, and modelled by a lamppost containing hybrid electrons and located very close to the horizon, which emission was incident on a surrounding disc extending almost to the innermost stable circular orbit. We re-analyse the incident continuum model and show that it suffers from the lack of physical self-consistency. Still, the good fit to the data provided by this model indicates that the real continuum has a similar shape. We find it features a strong soft X-ray excess below a few keV, which we model as a soft thermal-Comptonization component, in addition to the main hard thermal-Compton component. This continuum model with reflection of both components yields the overall lowest $\\chi^2$ and has a geometry with a hot inner accretion flow and a disc truncated at $\\simeq$13--20 gravitational radii. On the other hand, we have also found a spectral solution with a lamppost at a large height and a disc that can extend to the innnermost stable circular orbit. Overall, we find the fitted truncation radius depends on the assumed continuum and geometry.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-05-18T15:08:54.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "hard state",
      "truncated disc geometry",
      "suzaku observations",
      "stable circular orbit",
      "continuum model"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}