Science with e-ASTROGAM (A space mission for MeV-GeV gamma-ray astrophysics)

Abstract: e-ASTROGAM (enhanced ASTROGAM) is a breakthrough Observatory space mission, with a detector composed by a Silicon tracker, a calorimeter, and an anticoincidence system, dedicated to the study of the non-thermal Universe in the photon energy range from 0.3 MeV to 3 GeV - the lower energy limit can be pushed to energies as low as 150 keV for the tracker, and to 30 keV for calorimetric detection. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. Thanks to its performance in the MeV-GeV domain, substantially improving its predecessors, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on the surroundings. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous generation instruments, e-ASTROGAM will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LIGO-Virgo-GEO600-KAGRA, SKA, ALMA, E-ELT, TMT, LSST, JWST, Athena, CTA, IceCube, KM3NeT, and LISA.

• The paper highlights the mission’s innovative detector technology combining silicon trackers and calorimeters for high resolution and sensitivity.
• The paper addresses e-ASTROGAM’s capability to investigate extreme cosmic environments including GRBs, blazars, and multimessenger sources.
• The paper demonstrates how precise gamma-ray measurements can elucidate cosmic ray origins, nucleosynthesis, and overall Galactic chemical evolution.

Overview of the e-ASTROGAM Observatory Mission

The e-ASTROGAM mission represents a pivotal advancement in gamma-ray astronomical observation, targeting the energy range between 0.3 MeV and 3 GeV. Designed to probe the non-thermal universe, its detector technology combines unprecedented sensitivity, angular resolution, and polarimetric capabilities. These features enable groundbreaking observations of cosmic phenomena such as Galactic and extragalactic sources, mechanisms of supernova explosions, and contributions to cosmic chemical evolution.

Key Mission Objectives

The mission focuses on three main scientific domains:

1. Processes in Extreme Cosmic Environments: e-ASTROGAM is set to enhance our understanding of relativistic jets and outflows. Observations at energies transitioning between X-ray and TeV bands promise insights into particle acceleration processes and magnetic field dynamics in ultra-relativistic jets, particularly relevant for GRBs and blazars. Furthermore, it establishes the key energy range for detecting photons from multimessenger sources like gravitational waves and high-energy neutrinos.
2. Cosmic Ray Origins and Galactic Evolution: The mission aims to unravel cosmic ray origins affecting star formation and interstellar dynamics through gamma-ray observations. With optimal sensitivity for line emissions, e-ASTROGAM will distinguish gamma-ray and positron excesses toward Galactic regions, revealing nuclear synthesis in stars and aiding in identifying astrophysical sources tied to dark matter signals.
3. Nucleosynthesis and Galactic Chemical Enrichment: By achieving an unmatched sensitivity in line detection, e-ASTROGAM will illuminate isotopic production processes in stellar environments and trace historical events like supernovae within our galaxy. It facilitates precise cosmological studies by enhancing our understanding of Type Ia Supernovae as universal distance markers.

Instrumentation and Performance

e-ASTROGAM's technological framework comprises:

• Silicon Tracker: Utilizes Compton scattering and pair conversion to trace gamma-ray paths on high-resolution strips.
• Calorimeter: Measures energy deposits via thallium-doped cesium iodide, ensuring fine resolution.
• Anticoincidence System: Innovatively minimizes cosmic-ray background interference using scintillator shielding and time-of-flight discrimination.

These components orchestrate a wide field of view and rapid trigger capabilities enhancing the mission's sensitivity and its effectiveness in detecting GRBs and transient cosmic occurrences.

Implications and Future Prospects

The successful deployment of e-ASTROGAM promises extensive contributions to multimodal cosmic observations alongside facilities like CTA, SKA, and LIGO. By focusing on energy ranges poorly covered by previous missions, it will provide a clearer picture of cosmic ray propagation, non-thermal processes, and nucleosynthetic pathways. Its findings could redefine models of particle acceleration and the role of magnetic fields in cosmic environments, propelling theoretical and practical advancements in astrophysics.

In conclusion, e-ASTROGAM stands to not only complete missing pieces of high-energy astrophysical puzzles but also to offer unforeseen discoveries and establish a legacy for future observational facilities.