Multi-Messenger Astronomy: Cosmic Rays, Gamma-Rays, and Neutrinos

Abstract

Although cosmic rays were discovered a century ago, we do not know where or how they are accelerated. There is a realistic hope that the oldest problem in astronomy will be solved soon by ambitious experimentation: air shower arrays of 10,000 kilometer-square area, arrays of air Cerenkov telescopes and kilometer- scale neutrino observatories. Their predecessors are producing science. We will review the highlights: - Cosmic rays: the highest energy particles and the GZK cutoff, the search for cosmic accelerators and the the Cygnus region, top-down mechanisms: photons versus protons? - TeV-energy gamma rays: blazars, how molecular clouds may have revealed proton beams, first hints of the diffuse infrared background? - Neutrinos: first results and proof of concept for technologies to construct kilometer-scale observatories.