Survey of Ultrahigh Energy Cosmic Rays

Gamma-ray bursters are some of the most energetic events ever observed and have naturally been suggested as sources of ultrahigh energy cosmic rays. The presently accepted view is that ultrahigh energy cosmic rays are created and accelerated in active cosmic objects. Ultrahigh energy cosmic rays could be accelerated by the shock waves produced by the core collapse, or in the jets themselves. The overall spectrum of primary cosmic rays obeys an approximate power law with a break and a change of the slope at around a PeV. Neutron stars and black holes with accretion disks are almost certainly candidate sources of PeV energy galactic cosmic rays. An advantage of statistical acceleration models is that the observed power law energy spectrum is achieved in a natural way. Below about 0.1 PeV, the cosmic ray flux is sufficiently high to allow direct measurements to be performed on the primary particle.