New Mission Concept: Investigation of the Galactic Center with the Galactic Center Explorer (GalCenEx)

The European Space Observatory INTEGRAL has been providing excellent results on X-ray and gamma-ray astronomy since its launch in 2002. Among the most important results are the spectroscopy and imaging measurements of celestial gamma-ray sources, including mapping the 511 keV radiation from the Galactic plane. However, the nature of the 511 keV positron annihilation line around the Galactic Center region is still a mystery. Similarly, the structure and nature of the Galactic Center supermassive black hole and its surroundings, as well as the structure of heavily populated sky regions such as Cygnus and Carina in gamma-rays, remain unclear. We present a concept of a potential next-generation gamma-ray telescope with the major science objectives: a) solve the mystery of the Galactic Center region 511 keV positron annihilation line by mapping the Galactic Center region with high energy (<1% FWHM) and angular (< 10 arcmin) resolution and with line sensitivity <10(-5) ph cm(-2) s(-1); b) understand the nature of the Galactic Center supermassive black hole environment by creating a high-resolution spectral and intensity map of the surrounding region in 0.1 - 20 MeV gamma rays; and c) explore Galactic chemical evolution and sites of explosive element synthesis by conducting high-sensitivity measurements of nuclear lines from Type 1a supernovae and other objects. The instrument is based on a novel high-energy and position resolution CdZnTe Imager, coded aperture mask, and heavy-scintillator shield, and can be considered for a NASA Explorer mission.