NuSTAR and XMM-Newton observations of the hard X-ray spectrum of Centaurus A
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
- Department of Astrophysics/IMAPP, Radboud University Nijmegen, 6500 GL, Nijmegen (Netherlands)
- Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States)
- Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso (Chile)
- Lehrstuhl für Astronomie, Universität Würzburg, D-97074 Würzburg (Germany)
- Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)
- DTU Space, National Space Institute, Technical University of Denmark, DK-2800 Lyngby (Denmark)
- Dr. Karl-Remeis-Sternwarte and ECAP, D-96049 Bamberg (Germany)
- Department of Physics, Virginia Tech, Blacksburg, VA 24061 (United States)
- Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States)
- Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Menlo Park, CA 94025 (United States)
We present simultaneous XMM-Newton and Nuclear Spectroscopic Telescope Array (NuSTAR) observations spanning 3–78 keV of the nearest radio galaxy, Centaurus A (Cen A). 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 found 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 Γ = 1.815 ± 0.005 and a fluorescent Fe Kα line in good agreement with literature values. The spectrum does not require a high-energy exponential rollover, with a constraint of E{sub fold} > 1 MeV. A thermal Comptonization continuum describes the data well, with parameters that agree with values measured by INTEGRAL, in particular an electron temperature kT{sub e} between ≈100–300 keV and seed photon input temperatures between 5 and 50 eV. 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 outer 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 hard X-ray spectrum and conclude that the inner disk is replaced by an advection-dominated accretion flow or that the X-rays are dominated by synchrotron self-Compton emission from the inner regions of the radio jet or a combination thereof.
- OSTI ID:
- 22890141
- Journal Information:
- Astrophysical Journal, Vol. 819, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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