February 2-5, 2021

Oral Presentation

X-ray Constraint on Location of Torus in Circinus Galaxy

Author(s): Ryosuke Uematsu, Yoshihiro Ueda (Kyoto University), Atsushi Tanimoto (The University of Tokyo), Taiki Kawamuro (Universidad Diego Portales), Kenta Setoguchi, Shoji Ogawa, Satoshi Yamada (Kyoto University)

Presenter: Ryosuke Uematsu (Department of Astronomy, Kyoto University)

The location of the obscuring ``torus'' in an active galactic nucleus (AGN) is still an unresolved issue. The line widths of X-ray fluorescence lines originated from the torus, particularly Fe Kα, carry key information on the radii of line emitting regions. Utilizing XCLUMPY (Tanimoto et al. 2019), an X-ray clumpy torus model, we develop a realistic model of emission line profiles from an AGN torus where we take into account line broadening due to the Keplerian motion around the black hole. Then, we apply the updated model to the best available broadband spectra (3-100 keV) of the Circinus galaxy observed with Chandra, Suzaku, XMM-Newton, and NuSTAR, including 0.62 Ms Chandra/HETG data. We confirm that the torus is Compton-thick (NHeq=2.16^{+0.24}_{-0.16}×10^{25} cm^{-2}), geometrically thin (sigma=10.3^{+0.7}_{-0.3} deg), viewed edge-on (i=78.3^{+0.4}_{-0.9} deg), and has super-solar abundances (Z=1.52^{+0.04}_{-0.06}). Analyzing the Chandra/HETG multi-order spectra with consideration of the spatial extent of the Fe K$\alpha$ emitting region, we constrain the inner radius of the torus to be 1.9^{+3.1}_{-0.8}×10^5 times the gravitational radius, or 1.6^{+1.5}_{-0.9}×10^{-2} pc for a black hole mass of (1.7±0.3)×10^6 M(solar). This is about 3 times smaller than that estimated from the dust sublimation radius, suggesting that the inner side of the dusty region of the torus is composed of dust-free gas.

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