标题： 黑洞超紧凑X射线双星：银河系低频引力波源 显示英文标题

标题： Black Hole Ultra-compact X-ray Binaries: Galactic Low-Frequency Gravitational Wave Sources

摘要： 在银河系中，包含致密天体的密近双星是重要的低频引力波（GW）源。 作为潜在的低频GW源，中子星/白矮星（WD）超紧凑X射线双星（UCXBs）已被广泛研究。 使用MESA代码，我们系统地研究了黑洞（BH）-主序星（MS）双星的演化，以诊断其后代是否可以被空间引力波探测器检测到。 我们的模拟显示，初始轨道周期小于分岔周期的BH-MS双星可以演化成可被LISA检测到的BH UCXB。 这种演化途径将形成紧凑的质量转移BH-WD系统，而不是分离的BH-WD系统。 在距离$d=1$ kpc处被LISA检测到的BH UCXB的X射线光度为$\sim10^{33}-10^{35}~\rm erg\,s^{-1}$ ($\sim10^{34}-10^{35}~\rm erg\,s^{-1}$ 对于$d=10$ kpc)，因此有可能检测到它们的电磁对应体。 值得强调的是，只有初始轨道周期非常接近分岔周期的BH-MS系统才能演化成低频GW源，其啁啾质量可以被测量。 通过BH-MS路径形成的BH UCXB的最大GW频率约为3 mHz，小于通过动态过程产生的质量转移BH-WD的最小GW频率（6.4 mHz）。 此外，我们获得了BH UCXB-GW源前身的初始参数空间（供体恒星质量和轨道周期），可用于未来的群体合成模拟。 通过粗略估计，我们预测LISA只能检测到少数通过BH-MS通道形成的BH UCXB-GW源。 显示英文摘要

摘要： In the Galaxy, close binaries with compact objects are important low-frequency gravitational wave (GW) sources. As potential low-frequency GW sources, neutron star/white dwarf (WD) ultra-compact X-ray binaries (UCXBs) have been investigated extensively. Using the MESA code, we systematically explored the evolution of black hole (BH)-main sequence star (MS) binaries to diagnose whether their descendants can be detected by space-borne GW detectors. Our simulations show that BH-MS binaries with an initial orbital period less than the bifurcation period can evolve into BH UCXBs that can be detected by LISA. Such an evolutionary channel would form compact mass-transferring BH-WD systems rather than detached BH-WD systems. The calculated X-ray luminosities of BH UCXBs detected by LISA at a distance $d=1$ kpc are $\sim10^{33}-10^{35}~\rm erg\,s^{-1}$ ($\sim10^{34}-10^{35}~\rm erg\,s^{-1}$ for $d=10$ kpc), hence it is possible to detect their electromagnetic counterparts. It is worth emphasizing only some BH-MS systems with an initial orbital period very close to the bifurcation period can evolve toward low-frequency GW sources whose chirp masses can be measured. The maximum GW frequency of BH UCXBs forming by BH-MS pathway is about 3 mHz, which is smaller than the minimum GW frequency (6.4 mHz) of mass-transferring BH-WD originating from a dynamic process. Furthermore, we obtain an initial parameter space (donor-star masses and orbital periods) of progenitors of BH UCXB-GW sources, which can be applied to future population synthesis simulations. By a rough estimation, we predict that LISA could detect only a few BH UCXB-GW sources forming by the BH-MS channel.