模型无关搜索排除GWTC-4亚阈值候选体中的微弱引力波透镜对
Model-Independent Search Discards Faint Lensed-Pairs of Gravitational Wave Events in the Sub-Threshold Candidates of GWTC-4
AI总结：
使用基于互相关的GLANCE方法对GWTC-4全部应变数据进行模型无关的透镜搜索，未发现统计显著的亚阈值透镜事件，并将透镜探测率上限定为≤1.5/年。
摘要：
引力波的引力透镜效应在几何光学极限下可以产生多个像。这些透镜化的引力波像在不同时间到达，被不同的放大因子放大，并发生恒定相移。根据目前的理解，透镜事件的发生率约为每千次事件几次，而地面探测器网络探测到的引力波事件数量为几百次。然而，若包含亚阈值事件，总探测次数将超过几千次。因此，同时包含两类事件的搜索将获得更高的透镜探测几率。在本工作中，我们首次使用基于互相关的GLANCE技术对GWTC-4应变数据的全部体积进行模型无关的透镜搜索，该数据包含约90个超事件和约800个亚事件，共形成约11,000个事件对，具有较高的误报率，从而允许在噪声主导区域进行深度搜索。我们进一步对这些事件对进行频谱图检查以检验数据质量，检查感兴趣事件对的天空图重叠，并对亚事件进行贝叶斯参数探索，以实现稳健的透镜探测。尽管搜索指出了四对可能的事件，其互相关显著性≥2σ，但在LIGO-Hanford和LIGO-Livingston两个探测器中均未超过3σ。这使得我们可以强烈排除GWTC-4中存在任何统计显著的亚阈值透镜引力波事件。零探测结果将透镜探测率的上限定为≤1.5/年（包含亚阈值事件候选体）。未来，随着观测时间的增加，当前一代引力波探测器有可能探测到透镜化的引力波事件。
英文摘要：
Gravitational lensing of gravitational waves (GWs) can produce multiple images in the geometric optics limit. These lensed GW images arrive at different times, are amplified by different magnification factors, and are shifted by constant phases. With current understanding, the occurrence of lensed events stands at a few per thousand events, and the number of GW detections is a few hundred with the ground-based detector network. However, with the inclusion of the sub-threshold events, the total number of detections crosses a few thousand. Therefore, a search that includes both types of events yields a higher chance of lensing detection. In this work, we carry out the first model-independent lensing search using a cross-correlation-based technique GLANCE over the entire volume of the GWTC-4 strain data, containing $\sim 90$ super-events $\sim 800$ sub-events forming a total of $\sim 11,000$ event pairs with a higher False Alarm Rate (FAR) event rate allowing to search deep in the noise dominated regime. We further conduct their spectrogram checks to inspect data quality, sky-map overlap of the interesting pairs, and a Bayesian parameter exploration of the sub-event to make a robust lensing detection. Although the search indicated four pairs of potential events with cross-correlation significance $\geq 2σ$, none were above $3σ$ at both the LIGO-Hanford and LIGO-Livingston detectors. This makes it possible to strongly rule out the presence of any statistically significant sub-threshold lensed GW event in GWTC-4. The null detection translates to an upper bound on the lensing detection rate to be $\leq$ 1.5/yr with inclusion of the sub-threshold event candidates. In the future, with more observation time, the detection of lensed GW can be possible from the current generation of GW detectors.
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