Gamma-ray astronomy is study of astronomical objects using the most energetic form of electromagnetic radiation. Gamma-ray photons have many properties similar to photons of visible light and radio waves: they travel in straight lines; they move at the speed of light; and they are not affected by magnetic or electric fields in space. Because gamma rays can traverse great distances in space without absorption by intergalactic dust and gas, they can serve as powerful probes of distant regions of the cosmos as well as otherwise obscured regions of our own Milky Way Galaxy. Before the first gamma-ray observatories existed, scientists had already predicted that certain astrophysical phenomena, such as supernovae remnants, should produce gamma radiation. Development of the field of gamma-ray astronomy was also motivated by a related mystery: the origin of cosmic rays.
Relatively low energy gamma rays must be observed from space, but gamma rays with photon energies above about 50 GeV can be detected by ground-based telescopes that observe the light generated when the gamma rays strike molecules in the atmosphere. Fermi gamma-ray space telescope is designed for photon energies from 10 MeV to 300 GeV, while the ground-based VERITAS (Very Energetic Radiation Imaging Telescope Array System) covers 50 GeV to 10000 GeV. These observatories are expected to address important issues such as:
- Explain how black holes accelerate immense jets of material to nearly light speed.
- Help crack the mysteries of the stupendously powerful explosions known as gamma-ray bursts.
- Answer long-standing questions across a broad range of topics, including solar flares, pulsars and the origin of cosmic rays.
- Search for signs of new laws of physics and what composes the mysterious Dark Matter.
- Explore the most extreme environments in the Universe, where nature harnesses energies far beyond anything possible on Earth.
For the first time, the new generation of space and ground-based gamma-ray observatories together will have an almost uninterrupted sensitivity to gamma rays across an incredible range of photon energies, with a factor of nearly one million from the least energetic gamma rays that can be detected by Fermi gamma-ray space telescope to the most energetic gamma rays detected by VERITAS.
- VERITAS is a new major ground-based gamma-ray observatory with an array of four 12m optical reflectors for gamma-ray astronomy in the GeV - TeV energy range. It consists of an array of imaging telescopes deployed such that they permit the maximum versatility and give the highest sensitivity in the 50 GeV - 50 TeV band (with maximum sensitivity from 100 GeV to 10 TeV). This VHE observatory will effectively complement
- VERITAS Education Web site
- AGIS is a next-generation ground-based gamma-ray observatory currently in the design and development phase. The goal is to improve the sensitivity over current instruments by an order of magnitude, which will likely be achieved by using a large array of telescopes to cover ~1km2 on the ground.
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V. Acciari et. al., The VERITAS Collaboration, VERITAS observations of the gamma-ray binary LS I +61 303, Ap. J. 679, 1427 (2008).
V. Acciari et. al., The VERITAS Collaboration, Observation of gamma-ray emission from the galaxy M87 above 250 GeV with VERITAS, Ap. J. 679, 397 (2008).