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 that builds upon the heritage of past and current missions improving the sensitivity and, very importantly, the angular resolution. This consists in combining a Compton telescope and a coded-mask telescope. We delineate the motivation for such a concept and we define the scientific goals for such a mission. 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 bridges 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 can disentangle the discrete sources from the truly diffuse emission. Individual Galactic and extragalactic sources are detected. This also allows to understand the gamma-ray Galactic center excess and the Fermi Bubbles, and to trace the low-energy cosmic rays, and their propagation in the Galaxy. Nuclear and annihilation lines are 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. Such an instrument also detects explosive transient gamma-ray sources, which, in turn, enables identifying and studying the astrophysical objects that produce gravitational waves and neutrinos in a multi-messenger context. By looking at a poorly explored energy band it also allows discoveries of new astrophysical phenomena.

Yet Another Sunshine Mystery: Unexpected Asymmetry in GeV Emission from the Solar Disk

“…Orlando et al (2023) highlighted the significance of synchrotron radiation from galactic cosmic-ray electrons in the quiet Sun, suggesting that radio to X-ray observations can offer valuable insights into the interplay of CRs and solar magnetic fields. Furthermore, forthcoming X-ray and MeV-GeV observations from missions like FOXSI (Ishikawa et al 2014), Gecco (Orlando et al 2022), ASTROGAM (De Angelis et al 2017), and AMEGO (McEnery 2017) will shed light on high-energy processes in the solar corona, while observations at TeV energies with HAWC (Albert et al 2018), LHAASO (Cao et al 2019), SWGO (Huentemeyer et al 2019), and ongoing MeV-GeV studies with Fermi-LAT will further enhance our understanding of the solar disk emission at VHE.…”

Updated constraints on primordial black hole evaporation

“…Note that the limits on the 511 keV flux from the LMC and M31 are limited by the sensitivity of the SPI spectrometer. Future telescopes such GECCO [36], 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 have a field of view of ∼ 5−6 • , and a narrow-line sensitivity, in the best case scenario, of 7.4 × 10 −8 cm −2 s −1 , and in the worse case scenario 3.2 × 10 −7 cm −2 s −1 for point sources [37].…”

Detecting neutrino-boosted axion dark matter in the MeV gap

“…The Galactic Explorer with a Coded Aperture Compton Telescope (GECCO) [86] is a telescope designed to conduct high-sensitivity measurements of the gamma-ray light in the energy range from ∼ 0.2 MeV to 10 MeV and create intensity maps with high spectral and spatial resolution (∼ 1 − 2 angular resolution in the full energy range in mask mode). While most of the gamma-ray missions covering the MeV gap mainly focus on a Compton telescope, the GECCO mission combines a Compton telescope with the photoelectric regime with a coded mask.…”