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HESS (Adel. Internal)
High Energy Astrophysics Group (Adelaide Uni)
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Gamma-Ray photons represent the highest-energy electromagnetic radiation produced in nature. Low energy gamma-rays, from about 0.5 MeV up to several 10's of GeV can be detected directly from space-based instruments such as EGRET and the forthcoming GLAST. Ground-based methods come into play at higher energies, and have been highly successful in detecting gamma-rays from about 0.1 GeV up to several 10's of TeV (ground-based methods can in fact operate down to a few GeV). The study of TeV gamma-rays is motivated by our desire to understand where and how particle acceleration is taking place in extreme astrophysical environments. Gamma-rays are by far the most accessible tracer of particle acceleration in the Universe. Typical examples of extreme environments include supernove remnants, rotation-powered pulsar wind-nebulae, stellar assocations and sources with relativitis jet outflows such as microquasars and the central regions of active galaxies.
HESS (the High Energy Stereoscopic System) is an array of four identical telescopes located in Namibia (22deg South) that
image the Cherenkov radiation from extensive air shower (EAS) particles generated when a gamma-ray
enters and interacts with the Earth's atmosphere. The development of HESS draws on the experience gained from
previous telescopes, in particular the HEGRA CT-System which first demonstrated the potential of
stereoscopic observations. The picture to the left shows the HESS telescope array from above.
More details concerning HESS can be found at the HESS Collaboration website. Complementing this activity is
the study of molecular clouds in and around gamma-ray sources
at sub-mm wavelengths with telescopes such as NANTEN/NANTEN2, which helps in discerning the hadronic or leptonic
nature of the primary particles responsible for the gamma-ray emission, a key question related to the origin of accelerated particle or so-called cosmic-rays.
A glossy brochure with more details can be found here
Here is a brief list of the sources I have studied with HESS, HEGRA, CANGAROO, NANTEN, and other instruments:
- Centaurus A (the closest active galaxy)
- TeVJ2032+4130 (the first-known unidentifed TeV gamma-ray source)
- HESSJ1303-631 (The first HESS-discovered unidentifed TeV source)
- W28 (an old-age SNR with molecular cloud interaction)
- Tycho's SNR (a well-studied historical SNR)
- SN1006 (historical SNR with non-thermal X-ray emission)
- SS-433 (galactic jet source interacting with the surrounding ISM)
- LS5039 (High Mass X-ray binary with orbital modulation in its TeV gamma-ray emission)
A major area of interest is the study of high energy sources at E>10 TeV energies, an energy range
not adequately covered by existing intruments such as HESS. Our group is working on the design and
construction of a new array of small (10-30 m^2 dishes -- HESS dishes are about 100 m^2) gamma-ray telescopes optimised
for this purpose - called TenTen. This name is derived from its collection area and energy coverage
10 km^2 at energies above 10 TeV. Further details and motivation of this project can be found at this
page, which details a workshop we organised for this project.
Key information about high energy sources can come from their activity states at other wavelengths. Og high interest is the use of optical and radio telescopes to monitor Galactic transient sources such as X-ray binaries, SGR (soft-gamma-repeaters), AXP (anomalous X-ray pulsars) with a view to establishing trends in their multiwavelength output -- and to trigger TeV gamma-ray observations.