NGC 4945中的X射线反射器：时间和空间分辨的肖像
The X-ray reflector in NGC 4945: a time and space resolved portrait
摘要：
本文对NGC 4945中的X射线反射器进行了时间、光谱和成像分析，以前所未有的细节揭示了它的几何和物理结构。NGC 4945拥有天空中最亮的活动星系核之一，能量超过10 keV，但它只能通过其反射/散射的辐射在10 keV以下可见，这是因为它被约4 \times 10^24 cm-2的柱密度吸收。一个新的朱雀活动的5个观测跨越~6个月，连同过去的XMM牛顿和钱德拉观测，显示了显着的恒定性（<10%）的反射分量。相反，Swift-BAT在超过一年的时间尺度上显示出强烈的内在变异性。将环核气体模拟为轴在天空平面上的薄圆柱体，我们表明反射器的距离>30-50 pc，完全在钱德拉在NGC 4945（1”~18 pc）距离的成像能力范围内。因此，钱德拉成像揭示了一个解析的，扁平的，约150 pc长的星团结构，其光谱完全是由于原始活动星系核发射的冷反射。丛集现象可以解释由光谱和变率特性产生的小覆盖因子。
英文摘要：
We present a time, spectral and imaging analysis of the X-ray reflector in NGC 4945, which reveals its geometrical and physical structure with unprecedented detail. NGC 4945 hosts one of the brightest AGN in the sky above 10 keV, but it is only visible through its reflected/scattered emission below 10 keV, due to absorption by a column density of ~4\times10^24 cm-2. A new Suzaku campaign of 5 observations spanning ~6 months, together with past XMM-Newton and Chandra observations, show a remarkable constancy (within <10%) of the reflected component. Instead, Swift-BAT reveals strong intrinsic variability on time scales longer than one year. Modeling the circumnuclear gas as a thin cylinder with the axis on the plane of the sky, we show that the reflector is at a distance >30-50 pc, well within the imaging capabilities of Chandra at the distance of NGC 4945 (1"~18 pc). Accordingly, the Chandra imaging reveals a resolved, flattened, ~150 pc-long clumpy structure, whose spectrum is fully due to cold reflection of the primary AGN emission. The clumpiness may explain the small covering factor derived from the spectral and variability properties.
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