History of HEAG
Cosmic ray studies began at Adelaide when Ken McCracken took up a chair in the mid-1960s, mainly to develop the new field of balloon-borne x-ray astronomy, but also with a continuing interest in the properties of the heliosphere, and the use of cosmic ray monitoring to study those properties.
Theoretical work by the group looked at the propagation and scattering of low-energy galactic cosmic rays as they travel to us through the plasma and magnetic fields which fill the volume of space dominated by our sun. This theoretical work continued at Adelaide for many years, with an emphasis on much higher energies, typically in the multi-EeV range. Ray Protheroe was a long-term leader in propagation studies as they were developed to the highest-known energies.
The major concentration on cosmic rays at Adelaide began when John Prescott and Roger Clay arrived in mid-1971. John had been a full professor at the University of Calgary, Canada and in the late 1960s became interested in the new idea that extensive atmospheric cosmic ray showers (EAS) might produce pulses of radio energy. Such pulses would be detectable with conventional (and possibly cheap) radio receiving systems, and might offer a way of studying the EAS whilst in flight to the ground, as opposed to then conventional systems which only observed the shower in ground-based detectors.
Buckland Park facility
A cosmic-ray air-shower array was built at Buckland Park, a University field station 40km north of Adelaide. Radio measurements continued through the 1970s. The work of this era defined most of the important radio air-shower properties, but further progress was inhibited by background impulsive noise and the fact that some measurements were sensitive to time-varying geophysical processes. This work was revived in the late 1990's and benefited greatly from modern digital technologies.
A more productive technique promised to be the study of Cherenkov emission from EAS and the group (which now included Alan Gregory and John Patterson) developed techniques in this field, which became dominated by TeV gamma-ray astronomy studies and led to the construction of major gamma-ray telescopes at Woomera: BigRat and the CANGAROO series of telescopes, led by the ICRR at the University of Tokyo, and Adelaide. These instruments operated primarily during the late 1980s through to the early 2000s, though not both throughout all of that period.
A small optical observatory was established at Woomera in the mid-1990s, in order to undertake optical observations related to high-energy astrophysics. These included atmospheric extinction measurements, monitoring and characterisation of cataclysmic variable stars, and simultaneous optical/gamma-ray observations of active galactic nuclei. It was in use from 1994 to 1998.
The Buckland Park array was further developed through the 1980s and was used to develop sophisticated EAS observational techniques, plus making measurements of the directional properties of cosmic rays at PeV energies, which have only been surpassed recently by measurements taken by other researchers at the South Pole. However, at the end of the 1980s, it was clear that major - and unachievable - investment would be needed to maintain the Buckland Park system as a forefront instrument and new cosmic ray opportunities were explored.
Adelaide had developed close ties with the University of Utah and joined in collaboration to work on the Fly's Eye air fluorescence telescope and its successors at EeV energies. It also explored the possibility of using the Cherenkov effect in lake water (testing was undertaken at Mount Gambier's Blue Lake) to detect energetic cosmic neutrinos. The Fly's Eye fluorescence technique resulted in Bruce Dawson and Roger Clay being associated with the foundation of the highly successful Pierre Auger Observatory. The workshop which defined the basic observatory parameters was held in Adelaide in 1993.
The current interests at Adelaide followed from the foundations briefly discussed above. Adelaide is now an active member of the three most important ground-based high-energy astrophysics collaborations: the Pierre Auger Observatory (Bruce Dawson, Roger Clay and Jose Bellido Caceres, cosmic ray astrophysics at the highest energies), H.E.S.S./CTA (Gavin Rowell, ground-based gamma-ray astronomy), and IceCube (Gary Hill, neutrino astrophysics using ice below the South Pole).
HEAG facilities over the years
- Buckland Park: Particle detectors for cosmic ray studies. Also a muon counting system.
- White Cliffs: Modifications to a solar-power array test-bed for use as an atmospheric Cerenkov detector for ground-based gamma-ray astrophysics.
- Woomera: Development of the BIGRAT atmospheric Cerenkov gamma-ray telescope, and collaborations with ICRC (Japan) for multi-telescope ground-based Cerenkov observations; small optical observatory for cataclysmic variable star and active galactic nuclei photometry.
- Fly's Eye: Whilst not a HEAG facility, a strong connection between Adelaide and the University of Utah resulted in several Adelaide staff and students working on this early-generation cosmic-ray nitrogen fluorescence detector. The Fly's Eye was a step towards the Auger Observatory.