Exploring the MeV Sky with a Combined Coded Mask and Compton Telescope: The Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO)

Abstract

The sky at MeV energies is currently poorly explored. Here we present an innovative mission concept and we outline the scientific motivation for combining a coded mask and a Compton telescope. The Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO) is a novel concept for a next-generation telescope covering hard X-ray and soft gamma-ray energies. The potential and importance of this approach that will bridge the observational gap in the MeV energy range are presented. With the unprecedented angular resolution of the coded mask telescope combined with the sensitive Compton telescope, a mission such as GECCO will finally disentangle the discrete sources from the truly diffuse emission, unveiling the origin of the gamma-ray Galactic center excess and the Fermi Bubbles, and uncovering properties of lowenergy cosmic rays, and their propagation in the Galaxy. Individual Galactic and extragalactic sources will be detected, which will also allow studies of source populations. Nuclear and annihilation lines will be spatially and spectrally resolved from the 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 the chemical enrichment in the Galaxy. It will also detect explosive transient gamma-ray sources, which will enable identifying and studying the astrophysical objects that produce gravitational waves and neutrinos in a multi-messenger context. A GECCO mission will provide essential contributions to the areas "New Messengers and New Physics" and "Unveiling the Drivers of Galaxy Growth" emphasized in the Decadal Report on Astronomy and Astrophysics 2020.

Updated Constraints on Primordial Black Hole Evaporation

“…Note that the the limits on the 511 keV flux from the LMC and M31 are limited by the the sensitivity of the SPI spectrometer. Future telescopes such GECCO [31], whose science program includes specifically investigating the origin of the 511 keV emission in the Galactic center, will conduct high-sensitivity measurements of cosmic γ-radiation in the energy range from 100 keV-10 MeV. The GECCO instrument will [13,24] (purple line), and using extracted spectra utilizing NFW template [13](dashed purple line); upper limits on the flux of 511 keV line from LMC [26] (green band) and M31 [25] (brown band) from SPI upper limits.…”

Indirect dark-matter search with gamma-rays experiments : status and future plans from 300 KeV to 100 TeV

“…There is an energy range below the Fermi-LAT and AGILE energies that is not covered by any experiments. In this energy range a new instrument like Gamma-Light [30], e-ASTROGAM [31] or GECCO [32] is needed.…”

“…The very good angular resolution at low energies will help to resolve sources in the galactic center region and to desentangle a possible dark matter contribution ( see figure 9). In figure 10 the GECCO continuum sensitivity, compared with the sensitivity of other missions is shown [32].…”

Telescope Concepts in Gamma-Ray Astronomy

“…This results in an angular resolution of 12 arcmin within a field of view of 9 • . A proposed instrument that would extend these capabilities is GECCO, the Galactic Explorer with a Coded aperture mask Compton telescope [116]. GECCO's mask-detector separation would be about 20 m, resulting in a 4 • field of view with an angular resolution of 1 arcmin.…”