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

Lead Research Organisation: University of Leicester
Department Name: Physics and Astronomy

Abstract

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.

Planned Impact

Particle astrophysics, and specifically ground-based gamma-ray astronomy, necessarily requires engagement with industry; the nature of our work at the boundaries of particle physics and astronomy is such that technical innovation is vital. We have a track record of significant and successful engagement with industry. In addition, we have a strong commitment to outreach to schools and the general public, and have made an important contribution to outreach for CTA as a whole. Knowledge exchange and outreach are thus fundamental to our activities.

Amplifier Applications: A requirement for the prototype SST camera is the use of high-speed, low-noise, low-power, cheap amplifiers, which will be designed and built at the University of Leicester. These have potential uses in neutron detection, the aerospace industry, or for battery-powered hand-held devices.

Rapidly-Pulsed LEDs: Rapidly-pulsed LEDs are already used for applications such as fluorescence spectroscopy. These are expensive systems, ~£7k each - and there is likely a market for slightly slower but much cheaper device that will be developed as part of this proposal.

Construction: CTA will be a ~200 MEuro project, with substantial industrial involvement; there will be many opportunities for industrial contracts for the construction of both major components (inc. telescope structures) and smaller components.

We will use the excellent knowledge exchange infrastructure existing at the institutions involved to help us realise this programme. Opportunities for our public outreach programme include:

Outreach Website: The present CTA website www.cta-observatory.org was designed and almost entirely written by the CTA-UK team. This is designed to advertise CTA primarily to other scientists and scientifically literate members of the public. A CTA website for educators and the general public is presently being designed by Nolan at Durham University, and will be linked strongly also to the CTA-UK website, which will contin further, UK-specific resources for schools.

CTA Leaflet: We will produce a physical leaflet that can be handed to interested members of the public at talks, exhibitions etc. and hung on classroom walls as a poster. Nolan is drafting this with a view to production in early 2012.

Filming SST Construction: Both the prototype CTA telescope and future array construction need to be filmed for the production of documentary videos, films and webcasts about CTA. A Newcastle-based production company, Newton, has agreed to do some initial filming of the construction of the prototype SST in Paris without charge. Further, the filming of the prototype construction with Newton is proposed.

Planetarium Resources: The applicants are exploring with the National Space Centre (NSC) the possibility of creating a planetarium show based around CTA science.

Cosmic Rays in Schools: Greenshaw and Chadwick are part of the CORUS project to put cosmic ray detectors in ~30 UK schools. One of the project's aims is to produce teaching resources to go with the detectors; we will link the resources to CTA and provide extension material.

Exhibitions: 2012 is the 100th anniversary of the discovery of cosmic rays by Hess. We will apply to the Royal Society for an exhibit on cosmic rays and particle acceleration in the Universe for 2012. We will also ensure that we have a presence in the NSC exhibition.

The CTA-UK team has a great deal of outreach experience, and the outreach programme will be undertaken by researchers at all levels. There is also expertise available at CTA-UK institutions, including from outreach officers. For our early stage researchers, participation in outreach will be part of their training, and they will be encouraged to take part in media skills training. The UK members of CTA are already engaged with industry and the public; their collective experience will be used to aim for the highest possible economic and social impact for CTA in the UK.

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