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Ultra-high-energy cosmic rays

The origin of ultra-high-energy cosmic rays (E>1018 eV) is unknown. They form a tantalizing mystery: where do they come from, how do they get their high energies, how are their paths affected by intergalactic and Galactic magnetic fields, can we trace them back once detected on Earth?

Our focus points

The department focuses, together with the Department of High Energy Physics, on bringing low-frequency radio detection to maturity. This is a technique whose basis was laid in the 1960s but which could not be used for another forty years due to technological difficulties. We have brought this technique successfully to life and employed it both at LOFAR and at the Pierre Auger Observatory. Both observatories are now regularly taking data through both scintillator/water Cherenkov and radio observations (and in the case of Pierre Auger also fluorescence detectors). It is now a maturing field, where we are world-leading. Fascinating new insight into ultra-high energy cosmic rays as well as their propagation through Earth's atmosphere have been enabled by the radio technique.

Particular questions include:

  • How can we best use the hybrid techniques to understand ultra-high-energy cosmic rays?
  • What are the acceleration mechanisms for achieving ultrahigh energies, e.g. in jets or shocks?
  • Can we use radio power as a primary energy calibrator for ultra-high-energy cosmic rays?
  • Can we 'self-trigger', i.e. detect cosmic-rays by radio techniques alone, allowing a substantial increase in size and duty cycle of cosmic-ray detectors?

Use is made of theory, modelling (atmospheric propagation codes, both in the particle channel as well as the electromagnetic channel), and observations, in particular with LOFAR and at the Pierre Auger Observatory.

Goals for the next six years

  • Full-time usage of the LOFAR and Pierre Auger radio/scintillator particle arrays
  • Upgrade of the AERA array at Pierre Auger Observatory to cover 100 km2 ; upgrade of Auger itself. • Understanding the mass composition of high-energy cosmic rays from LOFAR/Auger studies
  • Does the Greisen-Zatsepin-Kuzmin cut-off exist?
  • What are the cosmic origins of ultra-high-energy cosmic rays?
  • How do cosmic rays propagate through galactic magnetic fields?

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