活动星系核中X射线灯柱冕大小的估算
Estimating the size of X-ray lamppost coronae in active galactic nuclei
摘要：
我们报告的活动星系核的X射线冠的大小在灯柱几何的估计。在这种普遍采用的方案中，为了简单起见，日冕被假定为位于吸积盘轴上的点状X射线源。然而，日冕必须拦截来自盘的与观察到的X射线通量一致的许多光学/UV种子光子，这限制了其尺寸。我们采用了最初由Dovčiak & Done（2016）开发的相对论射线追踪代码，该代码计算了由标准薄圆盘照明的康普顿化灯柱电晕的大小。我们假设圆盘向下延伸到非自旋或最大自旋黑洞的最内层稳定圆形轨道。我们将这种方法应用到一个样本的20个塞弗特1星系，同时使用光学/UV和X射线档案数据从XMM-牛顿。至少对于在爱丁顿极限以下吸积的源，我们发现康普顿化灯柱日冕通常可以存在，但是其大小和在黑洞的事件视界以上的高度取决于自旋。对于最大自旋的黑洞，几乎总是可以在任何高度找到解，而对于非自旋的黑洞，高度通常必须高于5个引力半径。这是因为，对于一个给定的光度，更高的自旋意味着更多的种子光子照亮日冕，由于更大和更热的内盘区域。最大自旋解是有利的，因为它预测的X射线光子指数与观测结果更吻合。
英文摘要：
We report estimates of the X-ray coronal size of active galactic nuclei in the lamppost geometry. In this commonly adopted scenario, the corona is assumed for simplicity to be a point-like X-ray source located on the axis of the accretion disc. However, the corona must intercept a number of optical/UV seed photons from the disc consistent with the observed X-ray flux, which constrains its size. We employ a relativistic ray-tracing code, originally developed by Dovčiak & Done (2016), that calculates the size of a Comptonizing lamppost corona illuminated by a standard thin disc. We assume that the disc extends down to the innermost stable circular orbit of a non-spinning or a maximally spinning black hole. We apply this method to a sample of 20 Seyfert 1 galaxies, using simultaneous optical/UV and X-ray archival data from XMM-Newton. At least for the sources accreting below the Eddington limit, we find that a Comptonizing lamppost corona can generally exist, but with constraints on its size and height above the event horizon of the black hole depending on the spin. For a maximally spinning black hole, a solution can almost always be found at any height, while for a non-spinning black hole the height must generally be higher than 5 gravitational radii. This is because, for a given luminosity, a higher spin implies more seed photons illuminating the corona due to a larger and hotter inner disc area. The maximal spin solution is favored, as it predicts an X-ray photon index in better agreement with the observations.
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