Mapping the circumnuclear regions of the Circinus galaxy with the Imaging X-ray Polarimetry Explorer

F. Ursini , A. Marinucci , G. Matt , S. Bianchi , F. Marin (1) , H. L. Marshall , R. Middei , J. Poutanen , A. De Rosa , L. Di Gesu , J. A. García , A. Ingram , D. E. Kim , H. Krawczynski , S. Puccetti , P. Soffitta , J. Svoboda , F. Tombesi , M. C. Weisskopf , T. Barnouin (1) , M. Perri , J. Podgorny (1) , A. Ratheesh , A. Zaino , I. Agudo , L. A. Antonelli , M. Bachetti , L. Baldini , W. H. Baumgartner , R. Bellazzini , S. D. Bongiorno , R. Bonino , A. Brez , N. Bucciantini , F. Capitanio , S. Castellano , E. Cavazzuti , S. Ciprini , E. Costa , E. del Monte , N. Di Lalla , A. Di Marco , I. Donnarumma , V. Doroshenko , M. Dovciak , S. R. Ehlert , T. Enoto , Y. Evangelista , S. Fabiani , R. Ferrazzoli , S. Gunji , J. Heyl , W. Iwakiri , S. G. Jorstad , V. Karas , T. Kitaguchi , J. J. Kolodziejczak , F. La Monaca , L. Latronico , I. Liodakis , S. Maldera , A. Manfreda , A. P. Marscher , I. Mitsuishi , T. Mizuno , F. Muleri , C. Y. Ng , S. L. O'Dell , N. Omodei , C. Oppedisano , A. Papitto , G. G. Pavlov , A. L. Peirson , M. Pesce-Rollins , P. -O. Petrucci (2) , M. Pilia , A. Possenti , B. D. Ramsey , J. Rankin , R. W. Romani , C. Sgrò , P. Slane , G. Spandre , T. Tamagawa , F. Tavecchio , R. Taverna , Y. Tawara , A. F. Tennant , N. E. Thomas , A. Trois , S. S. Tsygankov , R. Turolla , J. Vink , K. Wu , F. Xie , S. Zane

1 ObAS - Observatoire astronomique de Strasbourg
2 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble

We report on the Imaging X-ray Polarimetry Explorer (IXPE) observation of the closest and X-ray brightest Compton-thick active galactic nucleus (AGN), the Circinus galaxy. We find the source to be significantly polarized in the 2-6 keV band. From previous studies, the X-ray spectrum is known to be dominated by reflection components, both neutral (torus) and ionized (ionization cones). Our analysis indicates that the polarization degree is 28 ± 7 per cent (at 68 per cent confidence level) for the neutral reflector, with a polarization angle of 18^○ ± 5^○, roughly perpendicular to the radio jet. The polarization of the ionized reflection is unconstrained. A comparison with Monte Carlo simulations of the polarization expected from the torus shows that the neutral reflector is consistent with being an equatorial torus with a half-opening angle of 45^○-55^○. This is the first X-ray polarization detection in a Seyfert galaxy, demonstrating the power of X-ray polarimetry in probing the geometry of the circumnuclear regions of AGNs, and confirming the basic predictions of standard Unification Models.

Keywords: galaxies: active; galaxies: individual: Circinus; galaxies: Seyfert; polarization; scattering; X-rays: galaxies

Domains: Sciences of the Universe [physics]

F. Ursini, A. Marinucci, G. Matt, S. Bianchi, F. Marin, et al.. Mapping the circumnuclear regions of the Circinus galaxy with the Imaging X-ray Polarimetry Explorer. Monthly Notices of the Royal Astronomical Society, 2022, ⟨10.1093/mnras/stac3189⟩. ⟨insu-03850830⟩