Progress towards an advanced compton telescope

Abstract

With the termination of the Compton Observatory mission and the forthcoming launch of ESA’s INTEGRAL mission in 2002, plans for a follow-on low/medium-energy gamma ray mission are underway. NASA’s Gamma Ray Program Working Group has endorsed an Advanced Compton Telescope (ACT) as the next major mission for gamma ray astronomy. A Compton telescope instrument appears to be the best approach for meeting the sensitivity demands of a broad range of scientific objectives within acceptable cost and weight constraints. With a narrow line sensitivity of a −10−7 γ cm−2 s−1, gamma ray observations of many supernovae and novae will be realized for the first time. ACT will also provide detailed maps of the Galaxy in several nuclear lines associated with radioactive decays and cosmic ray interactions with the ISM. ACT will enable high sensitivity gamma ray studies of galactic compact objects, active galactic nuclei, and solar flares. The several components of the diffuse low-energy gamma ray background will be investigated. Alternative approaches for the instrument are presented, including the use of time projection chambers, position-sensitive solid-state detectors, and electron tracking in arrays of thin silicon strip detectors. A novel concept for using multiple Compton interactions to achieve high efficiency is discussed.