超越ISCO的冒险：探测来自黑洞周围俯冲区域的X射线发射
Venturing beyond the ISCO: Detecting X-ray emission from the plunging regions around black holes
摘要：
我们探讨如何X射线周围的黑洞的混响可能会揭示存在的最内层的稳定的圆形轨道（ISCO），预测由广义相对论，并探测之间的ISCO和事件视界的暴跌区域的动态。能够直接探测到ISCO的存在，并探测穿过事件视界的物质的动力学，代表了在强场区域对广义相对论的独特测试。X射线反射关闭的吸积盘和材料的暴跌区域建模使用广义相对论射线追踪模拟。来自俯冲区的X射线混响对时间平均X射线谱和总滞后能量谱的影响最小，但表现为最高频率傅立叶分量的滞后，高于0.01 c^3（GM）^-1（按黑洞的质量缩放）在2-4keV能带的非自旋黑洞或1-最大自旋黑洞的2keV能带。倾入区与圆盘发射的区别不仅在于倾入轨道的能量转移特征，而且在于通过倾入区的材料电离的快速增加。探测需要在这些频率上以20%的准确度测量时间滞后。将精确度提高到12%将能够对倾入区域的物质动态施加限制，并将倾入轨道与稳定圆形轨道上的剩余物质区分开来，从而证实国际空间观测组织的存在，这是未来X射线飞行任务的主要发现空间。
英文摘要：
We explore how X-ray reverberation around black holes may reveal the presence of the innermost stable circular orbit (ISCO), predicted by General Relativity, and probe the dynamics of the plunging region between the ISCO and the event horizon. Being able to directly detect the presence of the ISCO and probe the dynamics of material plunging through the event horizon represents a unique test of general relativity in the strong field regime. X-ray reverberation off of the accretion disc and material in the plunging region is modelled using general relativistic ray tracing simulations. X-ray reverberation from the plunging region has a minimal effect on the time-averaged X-ray spectrum and the overall lag-energy spectrum, but is manifested in the lag in the highest frequency Fourier components, above 0.01 c^3 (GM)^-1 (scaled for the mass of the black hole) in the 2-4keV energy band for a non-spinning black hole or the 1-2keV energy band for a maximally spinning black hole. The plunging region is distinguished from disc emission not just by the energy shifts characteristic of plunging orbits, but by the rapid increase in ionisation of material through the plunging region. Detection requires measurement of time lags to an accuracy of 20 per cent at these frequencies. Improving accuracy to 12 per cent will enable constraints to be placed on the dynamics of material in the plunging region and distinguish plunging orbits from material remaining on stable circular orbits, confirming the existence of the ISCO, a prime discovery space for future X-ray missions.
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