Origin of the Ultrahigh Energy Cosmic Rays and Their Spectral Break

TYPEAstrophysics Seminar
Speaker:Prof. Arnon Dar
Location:Lidow 620

The energy spectrum, composition and arrival directionss of ultrahigh energy cosmic rays (UHE-
CRs) with energy above the cosmic ray ankle that were measured by the Pierre Auger Observatory
are in conflict if the UHECRs are extragalactic in origin. Their observed properties, however,
are those expected from UHECRs which are accelerated by the highly relativistic jets emitted in
Galactic gamma ray bursts (GRBs), most of which are beamed away from Earth. In particular,
the observed break in the energy spectrum of UHECRs around 50 EeV that was identified as the
Greisen-Zatsepin-Kuzmin cutoff probably is the cosmic ray ankle of Galactic iron nuclei.