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

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 $28\pm 7$ per cent (at 68 per cent confidence level) for the neutral reflector, with a polarization angle of $18°\pm 5°$, 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.

9 pages, accepted for publication in MNRAS, authors list updated

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Cited by in corpus (13)

• Uncovering the geometry of the hot X-ray corona in the Seyfert galaxy NGC4151 with IXPE
• Cygnus X-3 revealed as a Galactic ultraluminous X-ray source by IXPE
• X-Ray Polarized View on the Accretion Geometry in the X-Ray Binary Circinus X-1
• X-ray polarization from accretion disk winds
• X-ray polarization measurement of the gold standard of radio-quiet active galactic nuclei : NGC 1068
• Studying geometry of the ultraluminous X-ray pulsar Swift J0243.6+6124 using X-ray and optical polarimetry
• Spectral and polarization properties of reflected X-ray emission from black-hole accretion discs for a distant observer: the lamp-post model
• Constraining the geometry of the dipping atoll 4U 1624-49 with X-ray spectroscopy and polarimetry
• Multi-epoch hard X-ray view of Compton-thick AGN Circinus Galaxy
• The innermost jet in the hidden ultra-luminous X-ray source Cygnus X-3
• Enhanced activity in close dual-AGN systems in the local Universe
• Instruments for Focal Plane X-Ray Polarimetry in the Next Decade
• Detection of Compton scattering in the jet of 3C 84