Gamma-ray spectroscopy: Requirements and prospects

Abstract

Observational results and theoretical work in the past 20 years have demonstrated the importance of high resolution gamma-ray spectroscopy to a wide range of topics in astrophysics. This work shows that a resolving power, E/ΔE, of ∼ 500 at 1 MeV is generally required to accurately measure gamma-ray line energics and determine their widths and profiles. However, with the exception of a few small instruments, the current and planned space missions in low energy gamma-ray and high energy X-ray astronomy, e.g. the GRANAT, Gamma-Ray Observatory and X-Ray Timing Explorer, do not contain high resolution spectrometers. Thus there is a compelling need for new missions which include high resolution gamma-ray spectrometers. These should be configured to study both point and diffuse sources. A sensitivity to narrow gamma-ray lines of a few x 10 −6 ph/cm 2-sec from ∼ 10 keV to ∼ 10 MeV, i.e. 100 x below the known line fluxes is achievable with technology that is in development. This would allow a rich observational program. The observational requirements, techniques to achieve them and prospects for realizing a space mission with these capabilities are discussed.