UK participation in the pre-production phase of CTA - extension 2018-2019

宇宙中充满了能量巨大的粒子，它们以非常接近光速的速度运动。它们在很多方面影响着宇宙，影响着恒星的生命周期和星系的演化。这些粒子很难追踪，但可以通过产生伽马射线来揭示它们的存在。和低能射线x射线一样，伽马射线不能穿透地球大气层，通常用卫星望远镜来探测。然而，在极高能量（VHE）下，伽马射线非常少，用航天器探测它们是不可能的。幸运的是，在地面上可以通过它们在大气中相互作用时产生的蓝光（切伦科夫辐射）来观察它们。大气中切伦科夫辐射发出的光比星光微弱1万倍，所以需要大型镜子来收集它，而且由于闪光只持续几十亿分之一秒，所以需要超高速相机来记录它们。从目前的地面伽玛射线望远镜，如HESS，我们知道有大量的现象需要研究。VHE伽马射线望远镜已经探测到超新星爆炸的遗迹、双星系统、遥远星系中黑洞产生的高能射流、恒星形成区和许多其他物体。这些观测不仅可以帮助我们了解这些物体内部发生了什么，还可以回答与暗物质和时空本身的本质有关的基本物理问题。然而，我们已经达到了现有仪器所能做的极限，因此，来自全球31个国家的约1600名科学家和工程师聚集在一起建造了一种新仪器——切伦科夫望远镜阵列（CTA）。CTA将大大提高现有仪器的灵敏度，并将观测到的伽马射线的能量范围扩展到更低和更高的值。据预测，已知的VHE发射物体的目录将从目前已知的大约130个扩展到1000多个，我们可以期待在天体物理学和基础物理学的关键领域有许多新的发现。为了实现CTA的能量覆盖，需要三种不同尺寸的望远镜：小型（直径~4米）、中型（12米）和大型（23米）望远镜（分别为SSTs、MSTs和LSTs）。CTA将在北半球和南半球设置阵列。北阵将包括4个lst和25个mst。南部阵列将在其4个lst和25个mst的基础上增加一个由70个sst组成的广泛阵列，以研究主要在南部天空可见的最高能量现象。我们预计CTA南部地区的第一批望远镜将于2019年开始建造。目前有12所英国大学和实验室参与了CTA。英国各集团正把精力集中在建造sst上。我们已经生产了一种创新的双镜SST设计，伽马射线切伦科夫望远镜（GCT），它正在巴黎埃菲尔铁塔的视线内进行原型制作，我们正在建造两个原型相机，有不同的传感器，我们将在这个设备上进行测试。在这里，我们要求资金来完成原型相机的测试，使用测试结果来设计GCT的最终相机，并准备为最终的SST望远镜提供相机。我们还希望与英国工业界合作，为相机设计一种新的保护窗，可以阻挡一些背景光，使我们能够检测到更微弱的切伦科夫闪光。最后，我们希望为CTA开发数据分析技术，以确保英国科学家在第一批望远镜开始运行时就准备好分析CTA的数据。

The Universe is full of particles with energies so great that they are travelling at very close to the speed of light. They affect the Universe in many ways, influencing the life-cycles of stars and the evolution of galaxies. These particles are hard to trace, but can reveal their presence by producing gamma rays. Like their lower-energy cousins, X-rays, gamma rays do not penetrate the Earth's atmosphere and usually satellite-based telescopes are used to detect them. However, at very high energies (VHE) there are so few gamma rays that detecting them using spacecraft becomes impossible. Luckily, it is possible to observe them from the ground via the flashes of blue light, Cherenkov radiation, produced when they interact in the atmosphere. The glow from Cherenkov radiation in the atmosphere is 10,000 times fainter than starlight, so large mirrors are required to collect it, and because the flashes last only a few billionths of a second, ultra-fast cameras are needed to record them. We know from current ground-based gamma-ray telescopes such as HESS that there is a wealth of phenomena to be studied. VHE gamma ray telescopes have detected the remains of supernova explosions, binary star systems, highly energetic jets produced by black holes in distant galaxies, star formation regions, and many other objects. These observations can help us to understand not only what is going on inside these objects, but also answer fundamental physics questions relating to the nature of Dark Matter and of space-time itself. However, we have reached the limit of what can be done with current instruments, and so about 1600 scientists and engineers from 31 countries around the world have come together to build a new instrument - the Cherenkov Telescope Array (CTA). CTA will offer a dramatic increase in sensitivity over current instruments and extend the energy range of the gamma rays observed to both lower and higher values. It is predicted that the catalogue of known VHE emitting objects will expand from the roughly 130 known now to over 1000, and we can expect many new discoveries in key areas of astrophysics and fundamental physics. To achieve the energy coverage of CTA, telescopes of three different sizes are needed: Small (~4 m diameter), Medium (12 m) and Large (23 m) Sized Telescopes (SSTs, MSTs and LSTs, respectively). CTA will have arrays in the northern and southern hemispheres. The northern array will consist of 4 LSTs and 25 MSTs. The southern array will add to its 4 LSTs and 25 MSTs an extensive array of 70 SSTs, to investigate the highest energy phenomena, visible mainly in the southern sky. We expect construction of the first telescopes on the CTA southern site to start in 2019. There are currently 12 UK universities and Laboratories involved in CTA. The UK groups are concentrating their efforts on the construction of the SSTs. We have produced an innovative dual-mirror SST design, the Gamma-ray Cherenkov Telescope (GCT), which is being prototyped in sight of the Eiffel Tower in Paris, and are building two prototype cameras, with different sensors, we will test on this device. Here we ask for funding to complete tests of the prototype camera, use the results to design the final camera for the GCT and to prepare for contributing cameras for the final SST telescopes. We also want to work with UK industry a new protective window for the camera that will keep out some of the background light, enabling us to detect fainter Cherenkov flashes. Finally, we want to develop data analysis techniques for CTA, to ensure that UK scientists are ready to analyse the data from CTA as soon as the first telescopes start operation.