KEEPING WATCH ON FARTHEST FRONTIERS

Irish Times
Published: Apr 19, 2007

Scientists are using data from a new telescope to study the most
violent events in the universe, writes Dick Ahlstrom.

A new research group has formed that puts Irish scientists at the very
frontiers of astro-particle physics research. The team will have full
access to the latest data coming from an advanced telescope system
known as Hess.

The new group has formed at the Dublin Institute for Advanced Studies
(Dias) under the leadership of Prof Felix Aharonian, an international
expert in cosmic ray physics. He is assembling a group of five or six
researchers who will process data coming from Hess, the High Energy
Steroscopic System based in Namibia.

Hess is an array of four 13-metre Cherenkov telescopes. These are
advanced instruments that can capture the difficult to see "Cherenkov
light", a blue glow given off when high energy particles such as gamma
rays and cosmic rays strike our upper atmosphere, explains Aharonian.

The Cherenkov light seen by Hess provides previously unavailable
information about the type of astro-particle involved, the direction
it came from and insights into the source of these particles.

Originally from Armenia, Aharonian comes to Dias via the Max-Planck
Institute in Heidelberg where he leads a high energy physics research
group. He will now divide his time between Dublin and Heidelberg,
which in turn gives Ireland unprecedented access to Hess data.

In Heidelberg he worked in two main areas, "the development of
theoretical aspects of high energy gamma ray sources and the
development of techniques for the detection of these gamma rays",
he says. "It was a mixture of theory and experiments."

The opportunity arose to set up a research group in Dublin and
Aharonian took it. "The reason was an exciting new group and an
interesting environment," he says. His group here will concentrate
on interpreting data from Hess.

"The new group will work on theory and interpretation of results of
Hess and data analysis. We want to play a significant role in this
activity and become one of the leading centres for this work. Now we
are really going to become one of the leading groups."

Stereoscopic systems observing Cherenkov light have transformed
research in this area, he says. "Hess was a revolution in this
field." It gives unique information about the source of the high
energy particles.

Gamma-rays given off by sources such as supernova remnants, pulsars
and star formation pass freely through intergalactic radiation and
magnetic fields.

This makes them unique carriers of astrophysical and cosmological
information about the most energetic and violent processes in the
universe, he explains.

The incoming gamma rays are absorbed by the atmosphere however,
producing a cascade of high energy particle collisions that produce
Cherenkov light.

It is a huge challenge to image Cherenkov light, but Hess now provides
an exceptional view of this light and hence the nature of the incoming
gamma rays.

"If you could image this light you could get ideas about the particles
and also the direction they come from," says Aharonian.

Hess was built specially to capture Cherenkov light and the reason
it works so well is because of the atmosphere. "The atmosphere is
part of the detector because it absorbs the particles."

Even so the technological challenges are considerable. The amount of
light being detected is "tiny" he says, requiring the use of large
mirrors to reflect the light into a detector. In turn the detector
must record the image very quickly, in just 10 billionths of a second
given the short-lived nature of Cherenkov light.

An advantage of having these instruments on the ground rather than
orbiting on board a satellite is the very wide angle view available
with Hess. It can observe 100,000 square metres at a time, essential
if you hope to catch these gamma-ray interactions.

They occur very infrequently. You might only expect to see three
interactions per square metre in a given year, so the wide view
increases the likelihood of capturing an event, says Aharonian.

Missions possible: sat data a boon to Irish researchers

Irish researchers now have greater access to data coming from some
of ESA’s most advanced satellites. These include orbiting instruments
that form part of the Agency’s Living Planet Programme.

The Republic became a member of ESA’s Programme Board Earth Observation
(PBEO) earlier this year and this now gives us access free of charge
to the streams of data coming from European satellites, according
to Barry Fennell of Enterprise Ireland. "This is extremely useful
data,"he says. "We are part of the PBEO and we can access the data
for research here."

The Living Planet programme includes two main components, a science and
research element in Earth Explorer missions and the Earth Watch element
which delivers earth observation data for eventual use in operational
services. There are data streams coming from meteorological satellites,
but now Irish scientists are invited to get involved at a much deeper
level, contributing to the definition of new missions, says Fennell,
who is the Irish delegate to PBEO and also the "national contact
point" for space science research under the EU’s research budget,
Framework Programme 7.

The Earth Explorer missions include a new strategy for observing
the earth, with satellite design reflecting issues raised by the
science community.

Scientists can get involved from the very beginning, enabling
researchers to get the most out of the data later delivered by these
satellites. This approach also gives Europe an excellent opportunity
for international cooperation, Fennell adds.

There are currently six missions in this category and a further
six undergoing assessment. The former are GOCE (Gravity Field and
Steady-State Ocean Circulation Explorer), SMOS (Soil Moisture and
Ocean Salinity), ADM-Aeolus (Atmospheric Dynamics Mission), CryoSat2
which studies the thickness of ice sheets and marine ice cover, Swarm,
a trio of satellites that will study the earth’s magnetic field and
EarthCARE (Earth Clouds Aerosols and Radiation Explorer).

These all launch from this year through 2012.