双黑洞轨道平面自旋取向的测量
Measuring binary black hole orbital-plane spin orientations
摘要：
双黑洞自旋是引力波天文学的重要观测量之一。在自旋参数中，它们在轨道平面内的取向，$ϕ_1$，$ϕ_2$和$Δϕ=ϕ_1-ϕ_2$，对于理解双黑洞中自旋轨道共振和合并反冲的普遍性是至关重要的。不幸的是，这些角度是特别难以测量使用当前的探测器，LIGO和处女座。由于旋进二进制的自旋方向不是恒定的，传统的方法是在波形演变中的某个参考阶段测量自旋分量，通常是检测信号的频率达到20 Hz的点。然而，我们发现，这是一个贫穷的选择轨道平面自旋角测量。相反，我们建议在合并附近的固定无量纲时间或频率测量自旋。这导致了对几个引力波事件的$ϕ_1$和$ϕ_2$的显著改进的测量。此外，使用数值相对论注入，我们表明，$Δϕ$也将更好地测量合并附近的更响亮的信号，预计在未来。最后，我们表明，数值相对论代理模型是可靠地测量轨道平面自旋取向的关键，即使在中等信噪比，如$\sim 30-45$。
英文摘要：
Binary black hole spins are among the key observables for gravitational wave astronomy. Among the spin parameters, their orientations within the orbital plane, $ϕ_1$, $ϕ_2$ and $Δϕ=ϕ_1-ϕ_2$, are critical for understanding the prevalence of the spin-orbit resonances and merger recoils in binary black holes. Unfortunately, these angles are particularly hard to measure using current detectors, LIGO and Virgo. Because the spin directions are not constant for precessing binaries, the traditional approach is to measure the spin components at some reference stage in the waveform evolution, typically the point at which the frequency of the detected signal reaches 20 Hz. However, we find that this is a poor choice for the orbital-plane spin angle measurements. Instead, we propose measuring the spins at a fixed dimensionless time or frequency near the merger. This leads to significantly improved measurements for $ϕ_1$ and $ϕ_2$ for several gravitational wave events. Furthermore, using numerical relativity injections, we demonstrate that $Δϕ$ will also be better measured near the merger for louder signals expected in the future. Finally, we show that numerical relativity surrogate models are key for reliably measuring the orbital-plane spin orientations, even at moderate signal-to-noise ratios like $\sim 30-45$.
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