UK Participation in the Preparatory Phase of the Cherenkov Telescope Array 2012-2015

宇宙中充满了能量极高的粒子，它们的运动速度非常接近光速。这些粒子在天体物理学的许多领域发挥着重要作用，从恒星的生命周期到星系的演化。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，从宇宙飞船上探测到它们是不可能的。幸运的是，在地面上可以通过它们在大气中引发的级联产生的蓝光（切列诺夫辐射）闪光来探测到它们。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，我们现在已经达到了现有仪器所能做的极限，因此，来自世界各地25个国家的约800名科学家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较低和较高的能量。据预测，已知的VHE发射天体的目录将从已知的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研究的关键领域有许多新的发现。为了实现我们对CTA的宽能量范围要求，需要建造三种不同尺寸的望远镜：~5米口径的小型望远镜（SSTs）、~12米口径的中型望远镜（MSTs）和~23米口径的大型望远镜（LST）。CTA将由两个望远镜阵列组成，一个在北半球，一个在南半球。北部阵列可能包括4个左右的lst和大约20个mst。南部阵列将包含类似数量的大型和中型望远镜，但增加了一个约50个sst的广泛阵列，专门用于研究可以优先从南半球观测到的最高能量现象。SSTs将探测到有史以来最高能量的光子，其能量接近1千兆电子伏特，每个光子的能量是x射线的1万亿倍。CTA目前处于筹建阶段，预计2015年开工建设。目前有11所英国大学参与了CTA。英国各集团正把精力集中在建造sst上。我们已经设计了一种创新的双镜SST设计，它将在巴黎埃菲尔铁塔的视野内建造。在这个提议中，我们要求资金做几件事。首先，我们想要建立和测试一个原型双镜SST相机，以及一个校准系统。其次，我们将利用我们在电脑模拟方面的专业知识，优化sst的设计和整体阵列布局。第三，我们将为CTA开发数据分析技术，以确保英国科学家能够在第一批望远镜开始运行时分析来自CTA的数据。最后，几位英国团队成员在CTA中担任领导角色，我们正在申请资金来支持这些人，并使我们能够前往参加相关会议。

The Universe is full of particles with such high-energies that they are travelling at very close to the speed of light. These particles play a significant role in many areas of astrophysics, from the life-cycles of stars to 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 very few gamma rays, and detecting them from spacecraft becomes impossible. Luckily, it is possible to detect them from the ground via the flashes of blue light, Cherenov radiation, produced by the cascades they initiate 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 now reached the limit of what can be done with current instruments, and so ~800 scientists from 25 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 extends the energy range of the gamma rays observed to both lower and higher energies. It is predicted that the catalogue of known VHE emitting objects will expand from the 130 known to over 1000, and we can expect many new discoveries in key areas of astrophysics and fundamental physics research. To achieve the wide energy range we require of CTA, it is necessary to build telescopes of three different sizes: ~5 m diameter small-sized telescopes (SSTs), ~12 m medium-sized telescopes (MSTs) and ~23 m large-sized telescope (LST). CTA will consist of two arrays of telescopes, one in the northern hemisphere and one in the southern hemisphere. The northern array will likely consist of 4 or so LSTs, and around 20 MSTs. The southern array will contain similar numbers of large and medium telescopes, but add to them an extensive array of ~50 SSTs, specifically to investigate the highest-energy phenomena which can be observed preferentially from the southern hemisphere. The SSTs will detect the highest energy photons ever seen, with energies approach a petaelectronvolt, each a thousand billion times more energetic than an X-ray. CTA is currently in its preparatory phase, and we expect construction to start in 2015.There are currently 11 UK universities involved in CTA. The UK groups are concentrating their efforts on the construction of the SSTs. We have already produced an innovative dual-mirror SST design, which will be built in sight of the Eiffel Tower in Paris. In this proposal we request funds to do several things. Firstly, we want to build and test a prototype dual-mirror SST camera, together with a calibration system. Secondly, we will use our expertise in computer simulations to optimise the design of the SSTs and the overall array layout. Thirdly, we will develop data analysis techniques for CTA, to ensure that UK scientists are able to analyse the data from CTA as soon as the first telescopes start operation. Finally, several UK team members have leadership roles in CTA and we are requesting funds to support these people and enable us to travel to the relevant meetings.