低频引力透镜成像计算

The first detection of gravitational waves has opened a new area in astronomy; it has been used to test many fundamental properties of gravity, e.g. the expansion rate of the universe, the speed of gravitational wave propagation, and to study the physics of binary black holes etc. As the detecting of gravitational waves become more refined, we will be able to see the CMB and the properties of the infant universe. Therefore, understanding the propagation of gravitational wave becomes extremely important. The gravitational lensing will affect the propagation of the wave and change the properties of the gravitational wave that we observe. We plan to calculate the lensing properties of wave optics, and analysis the time delay and magnification effects of wave lensing. For example, the time delay between the gravitational wave and the high-frequency radiation provides constraints on the cosmological distance..The pulsar timing array will provide gravitational wave detection as well. The arrival time of pulsar signal will be important. We find that the interstellar medium can change the luminosity and arrival time of the background radio sources, which can be formalized as plasma lensing. Besides the electron density, the density gradient can also cause large magnification and time delay. We will extend our previous work on plasma lensing into two dimensions, e.g. binary and elliptical models of the electron density. The plasma lensing can provide a possible solution for the extreme scattering event and the fast radio burst as well. By comparing with the observation, we can calibrate the pulsar arrival time and study the density profile of interstellar medium as well.

引力波的直接探测打开了天文学的全新领域。使一些基本的物理规律的检验成为可能，如，引力波传播的速度，和双黑洞的合并等。引力波在传播过程中与路径上的大质量天体的引力场相作用，会产生引力波的引力透镜现象。一方面，引力透镜会造成估算引力波源的性质时产生系统误差。但另一方面在引力波经过引力透镜时，会产生与电磁对映体不一样的时间延迟效应，我们可以利用这种时间延迟效应估算其距离，从而得到宇宙学信息。由于引力波的极低频特性，透镜方程需要重新计算，特别是其产生的时间延迟效应和可能的波动干涉效应。此外，利用脉冲星阵列也可以探测低频引力波，但是星际介质中的等离子体会对射电辐射的传播发生类似引力透镜的效应，如时间延迟，这将对引力波的探测造成系统误差。我们将系统计算此种等离子体透镜效应。在初步的计算中，我们已经建立了简单的一维模型。下一步将发展二维等离子体模型，从而能精确的估计其对脉冲星造成的时间延迟误差。

近年来射电观测技术迅猛发展，大视场射电巡天发现了越来越多的射电源特别是射电暂现源，如快速射电暴。宇宙中的星际介质对射电信号会产生一系列的影响，包括时间延迟和折射散射等，我们称之为等离子体透镜。本项目对等离子体透镜开展研究，构建了等离子体透镜模型，如几种解析模型的透镜特征，及其对射电信号的影响。我们还指出等离子体透镜对背景源光度函数的影响以及由此造成的对星系际介质估计的偏差。本项目工作结果将会对未来射电观测的分析研究有重要指导意义，特别是在利用快速射电暴研究宇宙学方面，我们指出几项重要系统偏差。本项目执行期间共发表英文sci论文9篇，其中8篇项目组成员为第一作者或通讯作者。还组织一次国际性学术会议，极大促进了相关课题的交流和发展。