Compton scatter imaging in astrophysics

Compton telescopes have been an important tool in gamma-ray astronomy, most recently with the COMPTEL instrument on NASA´s COMPTON Gamma Ray Observatory (CGRO). Scientific objectives in low/medium energy gamma-ray astronomy place highest priority on significant improvement in sensitivity relative to CGRO and ESA´s planned INTEGRAL mission. The observational requirements include both discrete and extended sources, and narrow, broad, and continuum spectral features. A high spectral and spatial resolution Compton telescope is the preferred instrument for a future mission. The broad range of scientific objectives that such a mission will address include: mapping radioactivity across the Galaxy ( ²⁶Al, ⁴⁴Ti, ⁶⁰Fe), detection of several Type Ia supernovae per year (⁵⁶Ni, ⁵⁶Co), study nuclear burning in novae (²²Na, ⁷Be, 511 keV), study the accretion of matter onto galactic and massive extra-galactic black holes and the associated formation of relativistic jets, and provide unique insights into neutron stars, cosmic gamma-ray bursts, and solar flares. A mission to achieve these goals should have discrete source, narrow line sensitivities approaching 10^-7 γ/cm ²-s for the important astrophysical gamma-ray lines from 511 keV to 2 MeV. Detectors which combine state-of-the-art energy resolution (few keV) and spatial resolution (1 mm) are required