Gravitational waves from binary neutron star inspirals have been detected along with the electromagnetic transients coming from the aftermath of the merger in GW170817. However, much is still unknown about the postmerger dynamics that connects these two sets of observables. This includes if, and when, the postmerger remnant star collapses to a black hole, and what are the necessary conditions to power a short gamma-ray burst and other observed electromagnetic counterparts. Observing the collapse of the postmerger neutron star would shed light on these questions, constraining models for the short gamma-ray burst engine and the hot neutron star equation of state. In this work, we explore the scope of using gravitational wave detectors to measure the timing of the collapse either indirectly, by establishing the shutoff of the postmerger gravitational emission, or—more challengingly—directly, by detecting the collapse signal. For the indirect approach, we consider a kilohertz high-frequency detector design that utilizes a previously studied coupled arm cavity and signal recycling cavity resonance. This design would give a signal-to-noise ratio of 0.5–8.6 (depending on the variation of waveform parameters) for a collapse gravitational wave signal occurring at 10 ms postmerger of a binary at 50 Mpc and with total mass $2.7M_{\odot }$. This detector design is limited by quantum shot noise and the signal-to-noise ratio largely depends on the detector power, which is adopted as 4 MW in this work. For the direct approach, we propose a narrow band detector design, utilizing the sensitivity around the frequency of the arm cavity free spectral range. To attain the maximal achievable quantum sensitivity, which is fundamentally limited by optical loss, we suggest the application of an optomechanical filter cavity that converts the signal recycling cavity into a signal amplifier. The proposed detector achieves a signal-to-noise ratio of 0.3–1.9, independent of the collapse time. This detector is limited by both the fundamental classical and quantum noise with the arm cavity power chosen as 10 MW.

中文翻译：

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用引力波探测器观测中子星坍塌

GW170817合并后，已经检测到来自中子星双星吸力的引力波以及电磁瞬变。但是，关于将这两套可观察变量连接起来的合并后动态仍然知之甚少。这包括合并后的剩余星体是否以及何时坍塌成黑洞，以及为短伽玛射线爆发和其他观测到的电磁对等体提供能量的必要条件是什么。观察合并后中子星的崩溃将为这些问题提供启示，从而限制了短伽玛射线爆发发动机和热中子星状态方程的模型。在这项工作中，我们探索了使用引力波探测器间接测量塌陷时间的范围，通过确定合并后引力发射的关闭，或更直接地，通过检测崩溃信号来确定挑战性。对于间接方法，我们考虑采用先前研究的耦合臂腔和信号循环腔谐振的千赫兹高频检测器设计。对于在50 Mpc的二进制合并后的10 ms发生的塌陷引力波信号，此设计将给出0.5–8.6的信噪比（取决于波形参数的变化），并且其总质量$2.7{\mathrm{中号}}_{\odot }$。这种探测器的设计受到量子散粒噪声的限制，信噪比在很大程度上取决于探测器的功率，在这项工作中，探测器的功率为4 MW。对于直接方法，我们提出了一种窄带检测器设计，该设计利用了围绕臂腔自由光谱范围频率的灵敏度。为了获得最大可实现的量子灵敏度，该灵敏度从根本上受到光损耗的限制，我们建议应用光机械滤波器腔，该腔将信号循环腔转换成信号放大器。拟议的探测器实现了0.3–1.9的信噪比，与崩溃时间无关。该检测器受到基本经典噪声和量子噪声的限制，臂腔功率选择为10 MW。