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

0569709 - ASÚ 2024 RIV GB eng J - Journal Article
Ursini, F. - Marinucci, A. - Matt, G. - Svoboda, Jiří - Podgorný, Jakub - Dovčiak, Michal - Karas, Vladimír … Total 97 authors
Mapping the circumnuclear regions of the Circinus galaxy with the Imaging X-ray Polarimetry Explorer.
Monthly Notices of the Royal Astronomical Society. Roč. 519, č. 1 (2023), s. 50-58. ISSN 0035-8711. E-ISSN 1365-2966
R&D Projects: GA ČR(CZ) GX21-06825X
Institutional support: RVO:67985815
Keywords : polarization * scattering * active galaxies
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 4.8, year: 2022
Method of publishing: Limited access
https://doi.org/10.1093/mnras/stac3189

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 degrees +/- 5 degrees, 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 degrees-55 degrees. 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.
Permanent Link: https://hdl.handle.net/11104/0341991