{
  "id": "1511.01915",
  "version": "v1",
  "published": "2015-11-05T21:09:46.000Z",
  "updated": "2015-11-05T21:09:46.000Z",
  "title": "NuSTAR and XMM-Newton Observations of the Hard X-Ray Spectrum of Centaurus A",
  "authors": [
    "F. Fuerst",
    "C. Mueller",
    "K. K. Madsen",
    "L. Lanz",
    "E. Rivers",
    "M. Brightman",
    "P. Arevalo",
    "M. Balokovic",
    "T. Beuchert",
    "S. E. Boggs",
    "F. E. Christensen",
    "W. W. Craig",
    "T. Dauser",
    "D. Farrah",
    "C. Graefe",
    "C. J. Hailey",
    "F. A. Harrison",
    "M. Kadler",
    "A. King",
    "F. Krauss",
    "G. Madejski",
    "G. Matt",
    "A. Marinucci",
    "A. Markowitz",
    "P. Ogle",
    "R. Ojha",
    "R. Rothschild",
    "D. Stern",
    "D. J. Walton",
    "J. Wilms",
    "W. Zhang"
  ],
  "comment": "13 pages, 6 figures, submitted to ApJ; comments are welcome",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We present simultaneous XMM-Newton and NuSTAR observations spanning 3-78 keV of the nearest radio galaxy, Centaurus A (Cen A), performed during a very high flux state. The accretion geometry around the central engine in Cen A is still debated, and we investigate possible configurations using detailed X-ray spectral modeling. NuSTAR imaged the central region of Cen A with subarcminute resolution at X-ray energies above 10 keV for the first time, but finds no evidence for an extended source or other off-nuclear point-sources. The XMM-Newton and NuSTAR spectra agree well and can be described with an absorbed power-law with a photon index {\\Gamma} = 1.815 +/- 0.005 and a fluorescent Fe K{\\alpha} line in good agreement with literature values. The spectrum does not require a high-energy exponential rollover, with a constraint of E_fold > 1MeV. A thermal Comptonization continuum describes the data well, with parameters that agree with values measured by INTEGRAL, in particular an electron temperature of kT_e ~ 220 keV, assuming a 10 eV seed photon input temperature. We do not find evidence for reflection or a broad iron line and put stringent upper limits of R < 0.01 on the reflection fraction and accretion disk illumination. We use archival Chandra data to estimate the contribution from diffuse emission, extra-nuclear point-sources, and the X-ray jet to the observed NuSTAR and XMM-Newton X-ray spectra and find the contribution to be negligible. We discuss different scenarios for the physical origin of the observed X-ray spectrum, and conclude that the inner disk is replaced by an advection-dominated accretion flow or that the hard X-rays are dominated by synchrotron self-Compton emission from the inner regions of the radio jet or a combination thereof.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-11-05T21:09:46.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "hard x-ray spectrum",
      "xmm-newton observations",
      "ev seed photon input temperature",
      "thermal comptonization continuum",
      "nearest radio galaxy"
    ],
    "publication": {
      "doi": "10.3847/0004-637X/819/2/150"
    },
    "note": {
      "typesetting": "TeX",
      "pages": 13,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1403143
    }
  }
}