用成像X射线偏振探测器绘制圆规星系的环核区域
Mapping the circumnuclear regions of the Circinus galaxy with the Imaging X-ray Polarimetry Explorer
摘要：
本文报道了利用成像X射线偏振探测器（IXPE）对距离我们最近、X射线最亮的康普顿厚度的活动星系核（AGN）--圆规星系的观测结果。我们发现源在2- 6 keV波段有明显的极化。从以前的研究中，X射线光谱被认为是占主导地位的反射成分，中性（环面）和电离（电离锥）。我们的分析表明，中性反射器的偏振度为$28 \pm 7$ %（置信水平为68%），偏振角为$18° \pm 5°$，大致垂直于射电喷流。电离反射的偏振是不受约束的。通过与蒙特卡罗模拟结果的比较表明，中性反射面与半张角为45° ~ 55 °的赤道环面是一致的。这是第一次在Seyfert星系中探测到X射线偏振，证明了X射线偏振测量在探测活动星系核周围区域几何结构方面的能力，并证实了标准统一模型的基本预测。
英文摘要：
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.
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