Speaker
Description
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 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 gamma-ray sky.
With the unprecedented angular resolution 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. Nuclear and annihilation lines will be spatially and spectrally resolved from continuum emission and from sources, addressing the role of low-energy cosmic rays in star formation and galaxy evolution, the origin of the 511 keV positron line, fundamental physics, and Galactic chemical evolution. Of special interest will be the exploration of sites of explosive element synthesis by conducting high- sensitivity measurements of nuclear lines from Type 1a supernovae and from other objects.
GECCO’s octagon-shaped active shield also serves as a powerful all-sky detector of gamma- ray bursts, prompting the instrument to slew towards the burst direction and localize it with the Coded Aperture’s arcminute accuracy. This unique feature enables the precise identification and study of astrophysical objects that produce gravitational waves and neutrinos in a multi-messenger context.
GECCO’s observational capabilities will be of paramount importance for disentangling astrophysical and dark matter explanations of emission from the Galactic Centre and potentially providing a key to discovering as-of-yet unexplored dark matter candidates. GECCO will operate in the 100 keV$-$10 MeV energy range, with energy resolution of $<1\%$ from 0.5$-$5 MeV.The Coded Aperture Mask provides the angular resolution of $\sim$1 arcmin with $4^\circ \times 4^\circ$ fully-coded field-of-view, while the Compton telescope provides the angular resolution of 4$^\circ-$8$^\circ$ with $60^\circ \times 60^\circ$field-of-view. The $3\sigma, 10^6 s$ sensitivity is expected to be about 10$^{-5}$ MeV cm$^{-2}$ s$^{-1}$over the entire energy range. GECCO can operate in either scanning or pointed mode. In scanning mode, it will mainly observe the Galactic Plane. It will change to pointed mode to either increase observation time for special regions of interest, (e.g., the Galactic Centre) or to observe transient events such as flares of various origins or gamma-ray bursts.
