Ultra-High-Energy Cosmic Rays: New Results from the Auger Array

The highest energy cosmic ray particles are the most energetic particles known to us in the universe, and their observations have led us to build one of the largest detector system in the world, the Auger air-shower
array. We have detected particles of an energy up to 3x10^20 eV, which is a macroscopic energy. There have been two predictions: one that due to interaction with the microwave background the spectrum
should show a turnoff near 5x10^19 eV; this has been confirmed by two experiments, HiRes and Auger. Second, that radio galaxies should be the accelerators, based on the non-thermal optical spectra of knots and hot spots in radio galaxies; this is now tentatively confirmed by Auger. Apart from differentiating various remaining options how to generate these particles, there is one major difficulty: the lack of understanding of the cosmological web of magnetic fields, which may influence the propagation of high energy particles; here it is especially important to understand the role of a galactic wind and its magnetic structure. In analogy to the scattering of particles in the Solar wind I propose, that this scattering leads to a steep distribution function of scattering angles of the deviation from a straight line path for the arriving particles. I will discuss the observational and theoretical limits for an exemplary set of models, the predictions, that result from these models, and how present and future observations will test our conclusions, especially with the Telecope Array (TA), the Auger Array, the neutrino observatory IceCube, and the future space observatory EUSO. There are a number of exciting consequences for high energy physics.

Dr. Peter Biermann
Max Planck Institute (Bonn)