Gamma-ray astronomy

Accretion disk A flattened, circulating disk of material drawn in and heated to high temperatures under the influence of the intense gravitational field associated with a black hole or other compact object (such as a neutron star or white dwarf). 

Bremsstrahlung The braking radiation given off by free electrons that are deflected (i.e., accelerated) in the electric fields of charged particles and the nuclei of atoms. 

Cosmic rays High-energy charged particles, such as electrons, protons, alpha-particles (helium nuclei), and heavier nuclei that propagate through interstellar space. 

Diffuse emission Radiation that is extended in angular size on the sky, such as the gamma-ray emission arising from the decay of radioactive nuclei dispersed throughout the interstellar medium. A diffuse source is distinguished from a pointlike or point source of emission that is not resolvable into further individual components given the limited angular resolution of a telescope. 

Electromagnetic cascades A phenomenon that occurs in the upper atmosphere of the Earth when a very high-energy gamma ray interacts by the pair-production process, followed by further interactions resulting in extensive air showers (or EAS) of particles and photons. The 

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They have been thrust to the forefront of cosmology, a boon for nuclear astrophysics The satellite INTEGRAL, dedicated to nuclear gamma-ray astronomy and on the point of spreading its wings, carries all the hopes and aspirations of the scientific community to which 1 belong. 

Keywords Imaging Air Cherenkov Telescopes, Gamma Ray Astronomy... 

The excess significance is 5.1 standard deviations (a), in accordance with the Li and Ma theory [9], which is usually applied within the gamma ray astronomy field. The initial significance was 5.6 a, it has been reduced in order to account for the position indetermination of the source. 

Fig. 1. The golden age of gamma-ray astronomy Never before the high-energy sky has been examined so thoroughly and over such a broad energy range.

The scientific potential of nuclear gamma-ray astronomy is outlined in section 2. In sections 3 instruments for spectroscopy in the low and medium gamma-ray channel are presented modulating aperture systems, Compton telescopes and diffraction lens telescopes. The three techniques actually reflect our current perception of light itself - they are based on the principles of geometrical optics, quantum optics and wave optics, respectively. 

With COMPTEL on the Gamma-ray Observatory, the concept has definitely proven its unique potential for MeV gamma-ray astronomy (Schonfelder et al. 1993). 

On a more distant horizon, experimental gamma-ray astronomy has to find ways to further push the limits of resolution and sensitivity At energies above one MeV, Compton telescopes can provide angular resolutions of fractions of degrees and sensitivities of a several 10"" ph cm s . At energies below the MeV, tunable crystal diffraction telescopes can achieve sensitivities of a few times 10"" ph cm s and angular resolutions of the order of 15". 

Key words gamma-ray astronomy - image processing - maximum entropy... 

Key words gamma-ray astronomy - diffuse emission - imaging - maximum entrof method-maximum likelihood method - bootstrap method - background... 

A Hybrid Detector Phoswich detectors are used extensively in hard x-ray/ gamma ray astronomy, but suffer from poor performance at low energies due to the small number of visible photons produced by the Nal crystal. The hybrid instrument [14, optically couples a 40 cm x 40 cm phoswich, currently... 

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