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Title: The 2-79 keV X-ray Spectrum of the Circinus Galaxy with NuSTAR, XMM-Newton and Chandra: a Fully Compton-Thick Active Galactic Nucleus

Here, the Circinus galaxy is one of the closest obscured active galactic nuclei (AGNs), making it an ideal target for detailed study. Combining archival Chandra and XMM-Newton data with new NuSTAR observations, we model the 2-79 keV spectrum to constrain the primary AGN continuum and to derive physical parameters for the obscuring material. Chandra's high angular resolution allows a separation of nuclear and off-nuclear galactic emission. In the off-nuclear diffuse emission, we find signatures of strong cold reflection, including high equivalent-width neutral Fe lines. This Compton-scattered off-nuclear emission amounts to 18% of the nuclear flux in the Fe line region, but becomes comparable to the nuclear emission above 30 keV. The new analysis no longer supports a prominent transmitted AGN component in the observed band. We find that the nuclear spectrum is consistent with Compton scattering by an optically thick torus, where the intrinsic spectrum is a power law of photon index Γ = 2.2-2.4, the torus has an equatorial column density of N H = (6-10) × 10 24 cm –2, and the intrinsic AGN 2-10 keV luminosity is (2.3-5.1) × 10 42 erg s –1. These values place Circinus along the same relations as unobscured AGNs in accretionmore » rate versus Γ and L X versus L IR phase space. NuSTAR's high sensitivity and low background allow us to study the short timescale variability of Circinus at X-ray energies above 10 keV for the first time. Here, the lack of detected variability favors a Compton-thick absorber, in line with the spectral fitting results.« less
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  1. Univ. Catolica de Chile, Santiago (Chile); Univ. de Valparaiso, Valparaiso (Chile)
  2. Univ. Catolica de Chile, Santiago (Chile); Space Science Institute, Boulder, CO (United States)
  3. ASDC-ASI, Roma (Italy); INAF Osservatorio Astronomico di Roma, Monte Porzio Catone (RM) (Italy)
  4. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  5. ETH Zurich, Zurich (Switzerland)
  6. Univ. of California, Berkeley, CA (United States)
  7. The Pennsylvania State Univ., University Park, PA (United States)
  8. Max-Planck-Institut fur extraterrestrische Physik, Garching bei Munchen (Germany)
  9. Danish Technical Univ., Lyngby (Denmark)
  10. INAF-Osservatorio Astronomico di Bologna, Bologna (Italy)
  11. Durham Univ., Durham (United Kingdom)
  12. Columbia Univ., New York, NY (United States)
  13. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  14. Univ. degli Studi Roma Tre, Roma (Italy)
  15. Univ. Catolica de Chile, Santiago (Chile); Univ. of Maryland, College Park, MD (United States)
  16. European Space Astronomy Centre (ESAC), Madrid (Spain)
  17. Univ. de Concepcion, Concepcion (Chile)
  18. Yale Univ., New Haven, CT (United States)
  19. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 1538-4357; arXiv:1406.3345
Grant/Contract Number:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 791; Journal Issue: 2; Journal ID: ISSN 1538-4357
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC); National Aeronautics and Space Administration (NASA)
Country of Publication:
United States
79 ASTRONOMY AND ASTROPHYSICS; Astrophysics; ASTRO; GRQC; axies: active; galaxies: individual (Circinus); galaxies: Seyfert; X-rays: galaxies