The world’s most sensitive Gamma Ray telescopes are
being inaugurated in Namibia (in Southwest Africa) on September 3rd.
The High Energy Stereoscopic System (H.E.S.S.), a European/African collaboration
in which the UK is a partner, will look for Gamma Rays produced by the most
energetic particles in the Universe. The array initially consists of four
telescopes, the first of which will become operational next week. This one
telescope alone is more sensitive than any other existing ground-based array or
telescope working in this particular area of the electromagnetic spectrum.

Once all four telescopes are operational in late 2003,
researchers from the University of Durham will use H.E.S.S. to investigate a
range of extreme cosmic environments such as the supernova remnants formed when
a star dies. A major goal is to see if these are a source of cosmic rays –
charged particles that constantly bombard the Earth from space. The origin of
cosmic rays is difficult to determine as they are influenced by the magnetic
field of our Galaxy. However, the Gamma Rays they emit travel in a straight
line, so they may reveal the primary source of the cosmic rays. H.E.S.S. will
also be probing the structure of pulsars (rapidly rotating stars formed when a
massive star explodes at the end of its life, which emit pulses across the range
of the electromagnetic spectrum) and active galactic nuclei to find the source
of their energy.

Dr Paula Chadwick, of the Durham team, explains: "H.E.S.S.
is set to give us unique insights into some of the most extreme environments in
the universe. We have some expectations about what we will be able learn more
about – supernova remnants, active galaxies and so on – but experience tells us
that when you improve the sensitivity of your telescope, you see things you
never expected as well. It’s going to be very exciting!"

When Gamma Rays are absorbed by the Earth’s atmosphere,
pairs of electrons and positrons are created and emit tiny flashes of light in a
process known as Cherenkov radiation. Telescopes such as H.E.S.S can detect
these tiny flashes of light. By using the Earth’s atmosphere as part of the
detector, the telescopes have much greater sensitivity than an equivalent space
based device, and can detect far fainter Gamma Ray sources than previously
possible.

Gamma rays are usually produced by particles moving
very rapidly. The study of Gamma Rays enables astronomers to learn more about
systems that accelerate these particles, such as active galactic nuclei where
supermassive black holes produce jets of particles travelling near the speed of
light. These are strong and highly variable sources of gamma rays. Gamma Rays
can also be produced by the annihilation of massive particles that may be the
source of the ‘missing mass’ in the universe.

The University of Durham’ s role in the design and
manufacture of HESS has been in calibrating the camera that will record the
Cherenkov radiation and in developing systems that will measure the atmospheric
conditions. This is critically important as variations in the atmosphere, such
as cloud cover, can dramatically reduce the amount of light reaching the
telescopes. The Durham scientists are now working on various refinements to
calibration systems, and a more efficient mirror making technique that they hope
to use when the array is extended from the current 4 telescopes to the planned
12 or 16.

Namibia is an excellent site scientifically, one of the
best in the world for ground-based optical astronomy and with ideal atmospheric
conditions for the techniques used by H.E.S.S. However, practically it has
represented a huge challenge with limited road access to the site and water,
power and computing connections having to be put in place specially.

Notes for Editors

Gamma Rays are a type of electromagnetic radiation,
like optical light or radio waves. Electromagnetic (em) waves have a wide range
of wavelengths and they can be used to see different views of objects. Visible
light only shows us what is on the surface, but other types of em waves can
reveal more, like the x-rays used by doctors to see broken bones. In their quest
to understand our universe, astronomers long ago branched out from visible light
to examine objects that radiate in the microwave and x-ray wavelengths. However,
gamma rays, the most energetic kind of EM wave have remained difficult to use
until now, as there are very few strong sources for astronomers to view.

H.E.S.S.

The H.E.S.S. array is named after Viktor Hess who
received the 1936 Nobel Prize in Physics for his discovery of cosmic radiation.

All four telescopes should be operational by late 2003,
at which point a decision will be made on whether to extend the project with
additional telescopes.

More details about the H.E.S.S. project can be found
at:
http://www.mpi-hd.mpg.de/hfm/HESS/HESS.html

Images are available from:
http://www.mpi-hd.mpg.de/HESS/public/full_images/full_images.htm
All pictures used should be credited to the H.E.S.S. collaboration.

Partners

University of Durham, United Kingdom

In Germany: Max-Planck-Institut f¸r Kernphysik,
Humboldt Universit‰t Berlin, Ruhr-Universit‰t Bochum, Universit‰t Hamburg,
Landessternwarte Heidelberg, Universit‰t Kiel,

In France: Laboratoire Leprince-Ringuet (LLR), Ecole
polytechnique, Palaiseau, LPC College de France, Paris, UniversitÈs Paris VI –
VII, France (LPHNE),UniversitÈ de Grenoble, CERS, Toulouse, CEA Saclay,
Observatoire de Paris-Meudon, DAEC,

Dublin Institute for Advanced Studies, Ireland
Charles University, Prag, Czech Republic,
Yerevan Physics Institute, Yerevan, Armenia
University of Namibia, Windhoek, Namibia
University of Potchefstroom, Republic of South Africa

Contact Details

Julia Maddock
PPARC Press Office
Tel 01793 442094
Email julia.maddock@pparc.ac.uk

Dr Paula Chadwick will be available for comment until
August 30th.
Email p.m.chadwick@dur.ac.uk
Tel 0191 374 7175

After August 30th, please contact:
Lowry McComb ( t.j.l.mccomb@dur.ac.uk
)
Mob: 0780 8551044
Tel: 0191 374 7175 or 01642 335323

Steve Rayner (
s.m.rayner@dur.ac.uk )
Tel: 0191 374 4562 or 0191 374 7175
Mob: 07941 803303

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 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 Laboratory for Particle Physics (CERN), the European Space
Agency [ESA] and the European Southern Observatory [ESO]. It also contributes
money for the UK telescopes overseas on La Palma, Hawaii, Australia and in
Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh
and the MERLIN/VLBI National Facility, which includes the Lovell Telescope at
Jodrell Bank observatory.