论文标题
使用nustar和XMM-在低亮度AGN NGC 3718中约束X射线反射
Constraining X-ray reflection in the low-luminosity AGN NGC 3718 using NuSTAR and XMM--Newton
论文作者
论文摘要
低亮度活性银河核（LLAGN）的一个独特特征是它们可能在X射线频谱中显示的相对较弱的反射特征，这可能是由于圆环的消失而导致的，并降低了积聚率。但是，某些材料必须围绕活性核，即吸积流本身以及可能是扁平或变薄的圆环。在这项工作中，我们研究了由于其本质上弱的特征以及LLAGN固有的低统计数据，因此反射是否确实没有或无法检测到。 Here we focus on NGC 3718 ($L/L_{\rm Edd}\sim10^{-5}$) combining observations from XMM--Newton and the deepest to date NuSTAR (0.5--79 keV) spectrum of a LLAGN, to constrain potential reflectors, and analyze how the fitted coronal parameters depend on the reflection model.我们测试代表积聚盘（Relxill）和圆环状（mytorus和Borus）中性反射器的模型。从统计的角度来看，不需要反射，但是其包含可以对周围环境的几何形状和物理特征施加强大的限制：所测试的两个中性反射器（圆环）应为Compton Thin（$ N_H <10^{23.2} $ CM $ cm $^{ - 2} $），并优先覆盖天空的大级别。如果反射的光相反产生电离反射器，则首选高度离子化的情况。这些模型在[1.81--1.87]范围内产生了固有的幂律光谱指数，其中圆环模型会导致斜坡较高。幂律排放的截止能也随着反射模型的包含而变化，从而导致圆盘反射器的限制值和圆环反射器的无约束值。
One distinctive feature of low-luminosity active galactic nuclei (LLAGN) is the relatively weak reflection features they may display in the X-ray spectrum, which can result from the disappearance of the torus with decreasing accretion rates. Some material, however, must surround the active nucleus, i.e., the accretion flow itself and, possibly, a flattened-out or thinned torus. In this work, we study whether reflection is indeed absent or undetectable due to its intrinsically weak features together with the low statistics inherent to LLAGN. Here we focus on NGC 3718 ($L/L_{\rm Edd}\sim10^{-5}$) combining observations from XMM--Newton and the deepest to date NuSTAR (0.5--79 keV) spectrum of a LLAGN, to constrain potential reflectors, and analyze how the fitted coronal parameters depend on the reflection model. We test models representing both an accretion disc (Relxill) and a torus-like (MYTorus and Borus) neutral reflector. From a statistical point of view, reflection is not required, but its inclusion allows to place strong constraints on the geometry and physical features of the surroundings: both neutral reflectors (torus) tested should be Compton thin ($N_H<10^{23.2}$cm$^{-2}$) and preferentially cover a large fraction of the sky. If the reflected light instead arises from an ionized reflector, a highly ionized case is preferred. These models produce an intrinsic power-law spectral index in the range [1.81--1.87], where the torus models result in steeper slopes. The cut-off energy of the power-law emission also changes with the inclusion of reflection models, resulting in constrained values for the disc reflectors and unconstrained values for torus reflectors.
