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Durham astrophysicist in team nominated for 2005 Descartes Research Prize

(13 July 2005)

A Durham University researcher is a key member of an international team taking part in a major experiment which is seeking to revolutionise the understanding of the extreme universe.

Dr Paula Chadwick of the Department of Physics is a member of the High Energy Stereoscopic System (HESS) collaboration which was formed to produce an instrument which would be the world leader in the domain of high-energy gamma-ray astrophysics.

The HESS project has now been nominated for a prestigious international scientific award. The Descartes Grand Jury has announced the shortlist for the 2005 Descartes Research Prize for, outstanding scientific work carried out by a multinational team of researchers.

These 14 projects will compete for a €1.15m scientific award. The winners of the 2005 award will be announced in London on 2 December. The shortlist was chosen from 85 submissions – three times more than in 2004. The 14 projects are made up of 76 teams from 22 countries across Europe and also from countries such as US, Japan, Russia, Singapore and South Africa. The Descartes Research Prize is awarded to teams of researchers who have achieved outstanding scientific and technological results through collaborative research. The prize is open to teams from all fields of scientific endeavour. The prize is awarded by the European Commission as part of its programme to increase contact between science and society.

The HESS design was based on proven technology and technical and experimental approaches develop by the research teams, which were combined together to provide an instrument that enabled them to explore the most extreme objects in the universe. The results of the project have allowed the collaboration to revolutionise the understanding of the universe as viewed in gamma rays, producing the first-ever gamma ray images of astronomical objects and the first scan of a large region around the centre of the galaxy.

The nomination comes in the same week as the HESS team of international astrophysicists reported in Science Magazine, the discovery of another new type of very high energy (VHE) gamma ray source. Gamma-rays are produced in extreme cosmic particle accelerators such as supernova explosions and provide a unique view of the high energy processes at work in the Milky Way. VHE gamma-ray astronomy is still a young field and H.E.S.S. is conducting the first sensitive survey at this energy range, finding previously unknown sources.

The object that is producing the high energy radiation is thought to be a 'microquasar'. These objects consist of two stars in orbit around each other. One star is an ordinary star, but the other has used up all its nuclear fuel, leaving behind a compact corpse. Depending on the mass of the star that produced it, this compact object is either a neutron star or a black hole, but either way its strong gravitational pull draws in matter from its companion star. This matter spirals down towards the neutron star or the black hole, in a similar way to water spiraling down a plughole.

Durham University’s Dr Paula Chadwick comments : "It's very exciting to have added another class of object to the growing catalogue of gamma ray sources. It's an intriguing object – it will take more observations to work out what is going on in there." The H.E.S.S. array is ideal for finding new VHE gamma ray objects; because it’s wide field of view (ten times the diameter of the Moon) means that it can survey the sky and discover previously unknown sources.

The results were obtained using the High Energy Stereoscopic System (H.E.S.S.) telescopes in Namibia, in South-West Africa. This system of four 13 m diameter telescopes is currently the most sensitive detector of VHE gamma-rays - radiation that is a million, million times more energetic than the visible light. These high energy gamma rays are quite rare even for relatively strong sources; only about one gamma ray per month hits a square metre at the top of the Earth's atmosphere. Also, since they are absorbed in the atmosphere, a direct detection of a significant number of the rare gamma rays would require a satellite of huge size. The H.E.S.S. telescopes employ a trick – they use the atmosphere as detector medium. When gamma rays are absorbed in the air, they emit short flashes of blue light, named Cherenkov light, lasting a few billionths of a second. This light is collected by the H.E.S.S. telescopes with large mirrors and extremely sensitive cameras and can be used to create images of astronomical objects as they appear in gamma-rays.

The H.E.S.S. telescopes represent several years of construction effort by an international team of more than 100 scientists and engineers from Germany, France, the UK, Ireland, the Czech Republic, Armenia, South Africa and the host country Namibia. The instrument was inaugurated in September 2004 by the Namibian Prime Minister, Theo-Ben Guirab, and its first data have already resulted in a number of important discoveries, including the first astronomical image of a supernova shock wave at the highest gamma-ray energies.

Contact : Dr Paula Chadwick University of Durham Tel : +44 191 334 3560 Fax: +44 191 334 5823 E mail: p.m.chadwick@durham.ac.uk mf Media : Julia Maddock PPARC Press Office Tel: 01793 442094 Mobile: 07901 514975 Email: julia.maddock@pparc.ac.uk

Notes for Editors Images Available from Gill Ormrod in the PPARC press office (01793 442012 or gill.ormrod@pparc.ac.uk) or PPARC website (post embargo time):- www.pparc.ac.uk/Nw/hess.asp The H.E.S.S. collaboration 1

• The High Energy Stereoscopic System (H.E.S.S.) team consists of scientists from Germany, France, the UK, the Czech Republic, Ireland, Armenia, South Africa and Namibia.
• Over the last few years, the H.E.S.S. collaboration has been building a system of four telescopes in the Khomas Highland region of Namibia, to study very-high-energy gamma rays from cosmic particle accelerators. The telescopes, known as Cherenkov telescopes, image the light created when high-energy cosmic gamma rays are absorbed in the atmosphere, and have opened a new energy domain for astronomy. The H.E.S.S. telescopes each feature mirrors of area 107 square metres, and are equipped with highly sensitive and very fast 960-pixel light detectors in the focal planes.
• Construction of the telescope system started in 2001; the fourth telescope was commissioned in December 2003. Observations were being made even while the system was being built, first using a single telescope, then with two and three telescopes. While only the complete four-telescope system provides the full performance, the first H.E.S.S. telescope alone was already superior to any of the instruments operated previously in the southern hemisphere.
• The Particle Physics and Astronomy Research Council (PPARC) is the UK’s strategic science investment agency. It funds research, education and public understanding in four broad areas of science - particle physics, astronomy, cosmology and space science.
• PPARC is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Organisation for Nuclear Research, CERN, the European Space Agency and the European La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility.