Multi-band, Multi-messenger Astrophysics with LIGO, LISA and GOTO

该奖学金研究引力波天文学的不同领域，从引力波探测到观测光学对应物并解释由此产生的天体物理含义。这将使用三个设施，LIGO（激光干涉仪引力波天文台），LISA（激光干涉仪空间天线）和GOTO（引力波光学瞬态天文台）。LIGO和LISA都是引力波探测器。LIGO在美国由两个探测器组成。它们对10hz到kHz范围内的引力波很敏感。LISA是一种未来的天基探测器，预计在本世纪30年代发射。LISA对0.1到100mhz的引力波很敏感。另一方面，GOTO是一个基于地球的光学望远镜。每当不对称物体加速时，就会发射引力波，可探测到的最强烈的引力波来自中子星和黑洞的碰撞。两者都是在大质量恒星生命结束时形成的。引力波天文学真正开始于2015年，当时LIGO首次观测到两个恒星质量黑洞碰撞的引力波特征。从那以后，一共观测到了11个引力波信号，其中10个来自两个黑洞的合并，1个来自两颗中子星的合并。后一个信号特别令人兴奋，因为在这个观测之前，人们只是猜测中子星碰撞会产生电磁信号。事实上，在2017年，这种双中子星合并不仅在引力波窗口中被观察到，而且在电磁波谱上也被观察到。在接下来的几年里，LIGO探测器将变得更加灵敏，能够看到更深入的宇宙，探测到更多的引力波。在这项研究中，我们将研究LIGO灵敏度的变化如何影响我们精确测量引力波信号特性的能力。我们还将开发技术来克服LIGO灵敏度较低的时期。我们希望确保引力波信号的关键参数，如天空位置、质量和源的自旋，是无偏的。这对于让我们将电磁望远镜指向正确的天空位置，了解原始双星系统的形成方式以及准确测量中子星的状态方程至关重要。对于LISA来说，我们必须探索如何最大限度地发挥未来任务的天体物理潜力。在这项研究中，我们将研究LISA灵敏度的预期变化将如何限制我们分离重叠引力波信号的能力。我们将研究克服模拟LISA数据灵敏度差的技术，以分离引力波信号并提取其天体物理性质。这项工作将增加我们识别意想不到的天体物理信号的机会，以及我们在所有尺度上预期的信号，从最小的恒星质量黑洞到星系中心碰撞的超大质量黑洞。这项研究的另一个方面是用GOTO望远镜跟踪引力波事件。到目前为止，只有一个引力波信号有一个确定的电磁对应。有了GOTO，我们将建立一个不同类型的光信号的目录，我们期望从不同的引力波源。这将使我们了解不同的光学特征是如何告诉我们潜在的天体物理学的。例如，我们将开始了解在两颗中子星的碰撞中产生了什么类型的物体。仅从引力波信号中很难推断出这些信息。我们还将研究双黑洞合并是否会产生光学对应物。光学特征的存在与否将开始表明这些合并黑洞最初是如何形成的。

This fellowship investigates different areas of gravitational-wave astronomy, from gravitational-wave detection to observing an optical counterpart and interpreting the resulting astrophysical implications. This will be done using three facilities, LIGO (Laser Interferometer Gravitational-wave Observatory), LISA (Laser Interferometer Space Antenna) and GOTO (Gravitational-wave Optical Transient Observatory). LIGO and LISA are both gravitational-wave detectors. LIGO consists of two detectors in the USA. They are sensitive to gravitational waves from 10 Hz to the kHz region. LISA is a future space-based detector, due for launch in the 2030s. LISA is sensitive to gravitational waves from 0.1 to 100 mHz. GOTO on the other hand is an Earth-based optical telescope.Gravitational waves are emitted whenever an asymmetric object accelerates, with the strongest sources of detectable gravitational waves being from the collision of neutron stars and black holes. Both are created at the end of a massive star's life. Gravitational-wave astronomy truly began in 2015 when LIGO observed the gravitational-wave signature of two stellar-mass black holes colliding for the first time. Since then a total of eleven gravitational-wave signals have been observed, ten from the merger of two black holes, and one from the coalescence of two neutron stars. This latter signal was particularly exciting, as prior to this observation it was just speculation that colliding neutron stars would produce an electromagnetic signal. Indeed, in 2017 this binary neutron star merger was not only observed in the gravitational-wave window, but also across the electromagnetic spectrum. Over the coming years the LIGO detectors will become more sensitive, seeing deeper into the Universe and detecting many more gravitational waves.In this fellowship, we will investigate how the changing nature of LIGO sensitivity affects our ability to accurately measure the properties of gravitational-wave signals. We will also develop techniques to overcome periods of poor LIGO sensitivity. We want to ensure that key parameters of the gravitational-wave signal, such as the sky location, masses and spins of the source, are unbiased. This is critical to allow us to point electromagnetic telescopes to the correct sky location, understand the way in which the original binary system formed and measure the equation of state of neutron stars accurately.For LISA, it is imperative that we explore how to maximise the astrophysical potential of the future mission. In this fellowship, we will investigate how the expected changing nature of the LISA sensitivity will limit our ability to separate overlapping gravitational-wave signals. We will investigate techniques to overcome times of poor sensitivity in mock LISA data to separate out gravitational-wave signals and extract their astrophysical properties. This work will increase our chances of identifying unexpected astrophysical signals, as well as those we expect on all scales, from the smallest stellar-mass black holes to the colliding supermassive black holes at the heart of galaxies.Another aspect of this research is to follow-up gravitational wave events with the GOTO telescope. So far, only one gravitational-wave signal has an identified electromagnetic counterpart. With GOTO, we will build a catalogue of the different types of optical signals we expect from different gravitational-wave sources. This will allow us to gain an understanding of how the different optical signatures inform us of the underlying astrophysics. For example, we will begin to understand what type of object is created in the collision of two neutron stars. This information is not easy to deduce from the gravitational-wave signal alone. We will also investigate whether a binary black hole merger will produce an optical counterpart. The presence or absence of an optical signature will begin to indicate how these merging black holes initially formed.