High-Energy Aspects of Astrophysical Jets

Various aspects of the high-energy emission from relativistic jets associated wi th compact astrophysical systems are reviewed. The main leptonic and hadronic processes responsible for the production of high-energy $\gamma$-rays, very-high energy neutrinos and ultra-high energy cosmic rays are discussed. Relations between the $\gamma\gamma$ pair production and photomeson production opacities are derived, and their consequences for the relative emission of $\gamma$-rays and neutrinos are examined. The scaling of the size and location of the various emission zones and other quantities with black hole mass and dimensionless luminosity is elucidated. The results are applied to individual classes of objects, including blazars, microquasars and gamma-ray bursts. It is concluded that if baryons are present in the jet at sufficient quantities, then under optimal conditions most systems exhibiting relativistic jets may be detectable by upcoming neutrino telescopes. An exception is the class of TeV blazars, for which $\gamma$-ray observations imply neutrino yields well below detection limit.