中性物质中Fe K α发射线的产生效率
On the efficiency of production of the Fe Kalpha emission line in neutral matter
摘要：
在天体物理源中，由X射线照射的物质产生的Fe Ka发射线的绝对光度是很难计算的，除非发射线的介质对于吸收和散射来说是光学薄的。我们的特征Fe Ka线通量使用无量纲效率，定义为分数的连续光子以上的Fe K壳吸收边阈值能量，出现在线。即使柱密度小到2 x 10^22 cm^-2，光薄近似也开始失效。我们将展示如何获得可靠的估计的Fe Ka线效率的情况下，冷，中性物质，即使是康普顿厚制度。我们发现，无论几何形状和覆盖因子，最大的Fe Kalpha线效率达到之前的介质成为康普顿厚。对于宇宙元素丰度，在最有利的条件和视线下，很难达到高于百分之几的效率。对于给定的几何形状，康普顿厚的视线可以具有比该几何形状的最大可能值小几个数量级的Fe Ka线效率。允许康普顿厚度反射表面的清晰视图的反射镜能够产生最高的效率。我们的结果可以用来估计窄Fe K α线在~6.4 keV的活动星系核的吸收模型的预测流量。特别是，我们表明，与最近的文献中的说法相反，在MCG-6 - 30 -15中相对论性Fe K α发射线的吸收主导模型对于任何柱密度或覆盖因子都不会过度预测窄Fe K α线。
英文摘要：
The absolute luminosity of the Fe Kalpha emission line from matter illuminated by X-rays in astrophysical sources is nontrivial to calculate except when the line-emitting medium is optically-thin to absorption and scattering. We characterize the Fe Kalpha line flux using a dimensionless efficiency, defined as the fraction of continuum photons above the Fe K shell absorption edge threshold energy that appear in the line. The optically-thin approximation begins to break down even for column densities as small as 2 x 10^22 cm^-2. We show how to obtain reliable estimates of the Fe Kalpha line efficiency in the case of cold, neutral matter, even for the Compton-thick regime. We find that, regardless of geometry and covering factor, the largest Fe Kalpha line efficiency is attained well before the medium becomes Compton-thick. For cosmic elemental abundances it is difficult to achieve an efficiency higher than a few percent under the most favorable conditions and lines of sight. For a given geometry, Compton-thick lines-of-sight may have Fe Kalpha line efficiencies that are orders of magnitude less than the maximum possible for that geometry. Configurations that allow unobscured views of a Compton-thick reflecting surface are capable of yielding the highest efficiencies. Our results can be used to estimate the predicted flux of the narrow Fe Kalpha line at ~6.4 keV from absorption models in AGN. In particular we show that contrary to a recent claim in the literature, absorption dominated models for the relativistic Fe Kalpha emission line in MCG -6-30-15 do not over-predict the narrow Fe Kalpha line for any column density or covering factor.
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