Fan Xi-Long, Liao Kai, Biesiada Marek, Piórkowska-Kurpas Aleksandra, Zhu Zong-Hong
School of Physics and Technology, Wuhan University, Wuhan 430072, China.
Departments of Physics and Mechanical & Electrical Engineering, Hubei University of Education, Wuhan 430205, China.
Phys Rev Lett. 2017 Mar 3;118(9):091102. doi: 10.1103/PhysRevLett.118.091102. Epub 2017 Mar 2.
We propose a new model-independent measurement strategy for the propagation speed of gravitational waves (GWs) based on strongly lensed GWs and their electromagnetic (EM) counterparts. This can be done in two ways: by comparing arrival times of GWs and their EM counterparts and by comparing the time delays between images seen in GWs and their EM counterparts. The lensed GW-EM event is perhaps the best way to identify an EM counterpart. Conceptually, this method does not rely on any specific theory of massive gravitons or modified gravity. Its differential setting (i.e., measuring the difference between time delays in GW and EM domains) makes it robust against lens modeling details (photons and GWs travel in the same lensing potential) and against internal time delays between GW and EM emission acts. It requires, however, that the theory of gravity is metric and predicts gravitational lensing similar to general relativity. We expect that such a test will become possible in the era of third-generation gravitational-wave detectors, when about 10 lensed GW events would be observed each year. The power of this method is mainly limited by the timing accuracy of the EM counterpart, which for kilonovae is around 10^{4} s. This uncertainty can be suppressed by a factor of ∼10^{10}, if strongly lensed transients of much shorter duration associated with the GW event can be identified. Candidates for such short transients include short γ-ray bursts and fast radio bursts.
我们基于强引力透镜引力波（GWs）及其电磁（EM）对应体，提出了一种新的与模型无关的引力波传播速度测量策略。这可以通过两种方式实现：比较引力波及其电磁对应体的到达时间，以及比较引力波及其电磁对应体中图像之间的时间延迟。引力透镜引力波-电磁事件可能是识别电磁对应体的最佳方式。从概念上讲，这种方法不依赖于任何关于大质量引力子或修正引力的特定理论。其差分设置（即测量引力波和电磁领域中时间延迟的差异）使其对透镜建模细节（光子和引力波在相同的透镜势中传播）以及引力波和电磁发射行为之间的内部时间延迟具有鲁棒性。然而，它要求引力理论是度规的，并且预测的引力透镜效应与广义相对论相似。我们预计，在第三代引力波探测器时代，这样的测试将成为可能，届时每年将观测到约10个引力透镜引力波事件。这种方法的能力主要受到电磁对应体定时精度的限制，对于千新星来说，定时精度约为10^{4} 秒。如果能够识别出与引力波事件相关的持续时间短得多的强引力透镜瞬变，这种不确定性可以被抑制约10^{10}倍。这种短瞬变的候选者包括短伽马射线暴和快速射电暴。
