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arXiv 2301.06243astro-ph.HEastro-ph.SR
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黑洞超致密X射线双星:银河系低频引力波源

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

Ke Qin, Long Jiang, Wen-Cong Chen

摘要:

在银河系中,具有致密天体的密近双星是重要的低频引力波源。中子星/白矮星超致密X射线双星作为一种潜在的低频GW源已被广泛研究。利用MESA程序,我们系统地研究了黑洞-主序星双星系统的演化过程,以诊断它们的后代能否被星载GW探测器探测到。我们的模拟表明,BH-MS双星的初始轨道周期小于分叉周期可以演变成BH UCXB,可以检测到的LISA。这样的演化通道将形成紧凑的传质BH-WD系统,而不是分离的BH-WD系统。LISA在距离$d=1$ kpc处探测到的BH UCXB的计算X射线光度为$\sim10^{33}-10^{35}~\rm erg\,s^{-1}$($\sim10^{34}-10^{35}~\rm erg\,s^{-1}$为$d=10$ kpc),因此有可能探测到它们的电磁对应物。值得强调的是,只有一些初始轨道周期非常接近分叉周期的BH-MS系统可以向低频GW源发展,其啁啾质量可以测量。通过BH-MS途径形成的BH UCXB的最大GW频率约为3 mHz,这小于源自动力学过程的质量传递BH-WD的最小GW频率(6.4mHz)。此外,我们还得到了BH UCXB-GW源的初始参数空间(施主星质量和轨道周期),这可以应用于未来的人口合成模拟。通过粗略的估计,我们预测LISA只能探测到由BH-MS通道形成的少量BH UCXB GW源。

英文摘要:

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.

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