GECCO: a Compton Telescope with Coded Aperture Mask

The Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO) is a novel Explorer-class concept for a next-generation telescope covering the poorly explored hard X-ray and soft gamma-ray energies. This concept builds upon the heritage of past and current missions, improving sensitivity and, very importantly, angular resolution. GECCO uses the combined Coded Aperture Mask and Compton telescope techniques to employ the benefits of both: superior angular resolution provided by the Coded Aperture, and good background rejection and wide field-of-view provided by the Compton telescope. It is being developed at NASA/GSFC in collaboration with BNL and other US and foreign institutions. GECCO observations will extend arcminute angular resolution to high-energy images of the Galactic plane, combining the spectral capabilities of INTEGRAL/IBIS and the x-ray imaging of NuSTAR and eROSITA, and will make a bridge to the Fermi-LAT observations, enabling a broad potential for discoveries in the MeV γ-ray sky. GECCO will operate in the 100 keV - 10 MeV energy range, with energy resolution of ~ 1% from 0.5 - 5 MeV. With the unprecedented angular resolution (∼1 arcmin) of the coded mask telescope combined with the sensitive Compton telescope, GECCO will be able to disentangle discrete sources from truly diffuse emission, contributing to understanding the gamma-ray Galactic Centre excess and the Fermi Bubbles, and to tracing low-energy cosmic rays and their propagation in the Galaxy.