DISCOVERY OF LOCALIZED TEV GAMMA-RAY SOURCES AND DIFFUSE TEV GAMMA-RAY EMISSION; .

Very high energy gamma-rays can be used to probe some of the most violent environments in the Universe, such as supernovae and supernovae remnants, pulsar-powered nebulae, and superluminal jets of active galaxies powered by super-massive black holes. The diffuse gamma radiation arising from the interaction of cosmic-ray particles with matter and radiation in the Galaxy is one of the few probes available to study the origin of cosmic-rays, whose origin is still a mystery a century after their discovery. Unlike charged cosmic-ray particles, gamma-ray photons are not bent in galactic and extra-galactic magnetic fields. They are also less easily absorbed by gas and dust in galaxies than light of longer wavelengths. Since there are very few of these photons, detection is done using ground instruments with large sensitive area. The main challenge for such instruments is to distinguish gamma-ray photons from the overwhelming background of hadronic cosmic rays. In this book, a new background rejection technique for the Milagro detector is presented. This new technique resulted in the discovery of three new VHE gamma-ray sources along with diffuse emission of VHE gamma-rays from the Galaxy.