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arXiv, 2022

DOI: 10.48550/arxiv.2211.01697

Oxford University Press, Monthly Notices of the Royal Astronomical Society, 1(519), p. 50-58, 2022

DOI: 10.1093/mnras/stac3189

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

Journal article published in 2022 by Francesco Ursini ORCID, Silvia Zane ORCID, Andrea Marinucci ORCID, Stefano Bianchi ORCID, Herman L. Marshall, Frédéric Marin ORCID, Juri Poutanen ORCID, Riccardo Middei ORCID, D. Rogantini, Giorgio Matt, Javier A. García, Laura Di Gesu, Adam Ingram, Henric Krawczynski, Alessandra De Rosa ORCID and other authors.
This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Abstract

ABSTRACT 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.