Arévalo, P.3; Bauer, F. E.3; Puccetti, S.4; Walton, D. J.18; Koss, M.19; Boggs, S. E.7; Brandt, W. N.20; Brightman, M.9; Christensen, Finn Erland1; Comastri, A.4; Craig, W. W.7; Fuerst, F.18; Gandhi, P.10; Grefenstette, B. W.18; Hailey, C. J.21; Harrison, F. A.18; Luo, Birong20; Madejski, G.12; Madsen, K. K.18; Marinucci, A.13; Matt, G.13; Saez, C.3; Stern, D.18; Stuhlinger, M.22; Treister, E.15; Urry, C. M.16; Zhang, W. W.23
1 National Space Institute, Technical University of Denmark2 Astrophysics, National Space Institute, Technical University of Denmark3 Pontifícia Universidade Católica4 National Institute for Astrophysics5 California Institute of Technology6 ETH Zurich7 University of California8 Pennsylvania State University9 Max-Planck-Institut10 Durham University11 Columbia University12 Stanford University13 Università degli Studi Roma Tre14 European Space Astronomy Centre15 Universidad de Concepcion16 Yale University17 NASA Goddard Space Flight Center18 California Institute of Technology19 ETH Zurich20 Pennsylvania State University21 Columbia University22 European Space Astronomy Centre23 NASA Goddard Space Flight Center
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 NH = (6-10) × 1024 cm-2, and the intrinsic AGN 2-10 keV luminosity is (2.3-5.1) × 1042 erg s-1. These values place Circinus along the same relations as unobscured AGNs in accretion rate versus Γ and LX versus LIR 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. The lack of detected variability favors a Compton-thick absorber, in line with the spectral fitting results.