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New Prospects in High

Recent discoveries using TeV, X-ray and radio telescopes as well as Ultra High Energy Cosmic Ray arrays are leading to new insights into longstanding puzzles in high energy astrophysics. Many of these insights come from combining observations throughout the electromagnetic and other spectra as well as evidence assembled from different types of source to propose general principles. Issues discussed in this general overview include methods of accelerating relativistic particles, and amplifying magnetic field, the dynamics of relativistic outflows and the nature of the prime movers that power them. Observational approaches to distinguishing hadronic, leptonic and electromagnetic outflows and emission mechanisms are discussed along with probes of the velocity field and the confinement mechanisms. Observations with GLAST promise to be very prescriptive for addressing these problems. PARTICLE ASTROPHYSICS IN THE 21ST CENTURY It is worth reminding ourselves at the start what an enormous fraction of the electromagnetic spectrum is commanded by “High Energy Astrophysics”1 . Conventionally this involves photons from ∼ 0.1 keV to the highest energy yet detected ∼ 100 TeV, a span of 33 octaves of energy. We can add a good share of the ten octave radio spectrum as well as the cosmic ray, neutrino, gravitational radiation spectra then this is more than half the available territory. Of course, there is far more going on physically in the single octave used by optical astronomers, but the high energy region contains important fundamental energies too. First, there are all the lines associated with heavy elements in the X-ray spectrum which allow us to make detailed inferences about the physical conditions density, temperature and so on as well as the bulk velocity of cosmic sources. At somewhat higher energy are the low energy nuclear emission lines, e.g. of cobalt and titanium. Next there is the electron-posittron rest mass ∼ 0.5 MeV which is the rest energy of a simple pair annihilation γ-ray. This is followed by the intermediate nuclear energy lines of deuterium and aluminium in the MeV range. Next comes the pion mass which gives a scale to the broad hadronic γray spectrum around ∼ 100 MeV. Finally there is the proton mass which marks a physics scale in many particle acceleration processes This may be made manifest in observed electromagnetic spectra. Although high 1 It is not possible in a review this broad to begin to do full justice to the immense bibliography in this area which represents a considerable amount of hard work and thought over more than forty years. Therefor I have just cited a few very general references at the end of this article where good entries into the literature may be found. SLAC-PUB-14755 Work supported in part by US Department of Energy contract DE-AC02-76SF00515. SLAC National Accelerator Laboratory, Menlo Park, CA 94025 energy astrophysics involves observing throughout the electromagnetic spectrum from ∼ 100 neV radio waves to ∼ 100 TeV γ-rays, it also embraces, or one day will embrace, the non-electromagnetic cosmic neutrino and gravitational radiation spectra.