X射线反射作为超大质量黑洞双星性质的诊断工具
X-ray Reflection as Diagnostic of Supermassive Black Hole Binary Properties
AI总结：
该研究通过计算24570个X射线反射谱，发现相对论性Fe Kα蓝峰位置可诊断双星倾角，监测Fe Kα质心可确定轨道相位并约束质量比，其方法可补充引力波测量以约束SMBH双星参数。
AI中文摘要：
我们研究了由吸积超大质量黑洞（SMBH）双星所产生的相对论性X射线反射谱中显著特征与双星系统基础性质之间的关联。对相对论性Fe Kα线（约6.4 keV）和康普顿反射驼峰（约20-30 keV）的模型无关测量被证明可用于约束双星参数。我们通过改变两个附着于SMBH的 mini-disk（ mini-disk 即 mini 吸积盘）的质量比、自旋参数、倾角、轨道相位和总吸积率，在固定间距为100 GM/c²的圆轨道上计算了24570个X射线反射谱。我们发现，相对论性Fe Kα的蓝峰位置是双星倾角的相对可靠诊断量，可从单epoch（单epoch即单时刻）X射线谱中获得。给定几个epoch的谱，人们或许能够通过监测Fe Kα的质心来确定双星的轨道相位并约束其质量比。在所有参数中，SMBH自旋的效应最为微弱且易出现测量简并。不过，由于辐射效率提高，高SMBH自旋的某些标记仍可能在复合谱中显现。本文所发展的方法可在完整的参数化X射线谱拟合方法可用之前，用于对双星参数进行初步约束。它通过对脉冲星计时阵列（PTAs）和空间激光干涉仪（Laser Interferometer Space Antenna）的引力波测量形成补充，提供对易出现简并（如倾角）或原本无法获取（如PTAs无法测量的自旋）的双星参数的独立约束。
英文摘要：
We investigate correlations between prominent features in the relativistic X-ray reflection spectrum emitted by an accreting supermassive black hole (SMBH) binary with the underlying properties of the binary system. Model-independent measurements of the relativistic Fe K$α$ line ($\sim$6.4 keV) and the Compton reflection hump ($\sim$20-30 keV) are shown to be useful in constraining binary parameters. We compute 24,570 X-ray reflection spectra from two mini-disks attached to SMBHs at a fixed separation of 100 $GM/c^2$ on circular orbits, by varying its mass ratio, spin parameters, inclination, orbital phase and total mass accretion rate. We find that the location of the blue peak in the relativistic Fe K$α$ is a relatively robust diagnostic of the binary inclination, which could be obtained from a single-epoch X-ray spectrum. Given a few epochs of spectra, one may be able to determine the orbital phase of the binary and place constraints on its mass ratio by monitoring the Fe K$α$ centroid. Of all parameters, SMBH spin efects are most subtle and prone to measurement degeneracies. Some markers of high SMBH spin may nevertheless surface in the composite spectrum due to increased radiative efficiency. The approach developed here can be used to place preliminary constraints on binary parameters before a full parametrized X-ray spectral fitting method is available. It complements gravitational wave measurements by the Pulsar Timing Arrays (PTAs) and the Laser Interferometer Space Antenna by providing independent constraints on binary parameters that may be prone to degeneracy (inclination), or otherwise inaccessible (spin for PTAs).
