[Paper Review] The e-ASTROGAM mission (exploring the extreme Universe with gamma rays in the MeV-GeV range)

A. De Angelis, V. Tatischeff+72 more|arXiv (Cornell University)|Nov 7, 2016

Astrophysics and Cosmic Phenomena141 references94 citations

TL;DR

e-ASTROGAM proposes a next-generation gamma-ray space observatory optimized for the MeV–GeV energy range, using a novel, low-material instrument design to detect over 3,000 sources within three years and provide polarization measurements for thousands. It enables multi-messenger astronomy by detecting transient sources, including gravitational wave counterparts, and supports rapid alerts for coordinated multi-wavelength follow-up.

ABSTRACT

e-ASTROGAM (`enhanced ASTROGAM') is a breakthrough Observatory mission dedicated to the study of the non-thermal Universe in the photon energy range from 0.3 MeV to 3 GeV. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. In the largely unexplored MeV-GeV domain, 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 Galactic ecosystems. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous generation instruments, 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 the promise of eLISA. Keywords: High-energy gamma-ray astronomy, High-energy astrophysics, Nuclear Astrophysics, Compton and Pair creation telescope, Gamma-ray bursts, Active Galactic Nuclei, Jets, Outflows, Multiwavelength observations of the Universe, Counterparts of gravitational waves, Fermi, Dark Matter, Nucleosynthesis, Early Universe, Supernovae, Cosmic Rays, Cosmic antimatter.

Motivation & Objective

• To significantly increase the number of known high-energy gamma-ray sources by more than an order of magnitude compared to current missions.
• To provide polarization measurements for thousands of gamma-ray sources, enabling new insights into emission mechanisms in extreme astrophysical environments.
• To support time-domain astronomy by detecting and localizing transient phenomena, including gravitational wave counterparts and flaring sources.
• To enable rapid, coordinated multi-wavelength observations by providing fast alerts and open access to the international scientific community.
• To complement ground-based and space-based observatories across the electromagnetic and particle spectrum, especially CTA, ALMA, JWST, and LHAASO.

Proposed method

• The mission employs a wide-field gamma-ray telescope based on a hybrid instrument combining a Compton camera (P/L detector) and a pair-conversion tracker (L/SCD), minimizing passive material to enhance sensitivity.
• The P/L detector uses a segmented scintillator array with position and energy resolution optimized for MeV–GeV gamma rays, with a full-energy peak energy resolution of 5% at 1 MeV.
• The L/SCD uses silicon strip detectors to track electron-positron pairs from pair production, enabling energy and direction reconstruction with high precision.
• The spacecraft is placed in a low Earth orbit (LEO) with a 3-year nominal lifetime, using a monopropellant hydrazine propulsion system for orbit correction and controlled re-entry.
• Attitude control is achieved via three-axis stabilization with reaction wheels and magnetic torquers, enabling precise pointing accuracy (±1°), stability (0.01°/s), and 30 arcsecond knowledge after processing.
• Thermal control is managed via large, fixed radiators (11.6 m² total) using Loop Heat Pipe (LHP) technology to dissipate 1.5 kW of payload heat, maintaining detector temperature between -10°C and 0°C.

Experimental results

Research questions

• RQ1 Can a low-material, wide-field gamma-ray instrument detect more than 3,000 sources in the MeV–GeV range within three years of operation?
• RQ2 To what extent can polarization measurements of high-energy gamma rays improve understanding of emission mechanisms in pulsars, AGNs, and other extreme sources?
• RQ3 How effectively can e-ASTROGAM localize and identify transient sources, such as gravitational wave counterparts or flaring transients?
• RQ4 What is the performance of a hybrid Compton + pair-conversion detector design in achieving high sensitivity and low background in LEO?
• RQ5 How can e-ASTROGAM enable rapid, coordinated multi-messenger follow-up through fast alert dissemination and open observatory access?

Key findings

• The instrument is projected to detect over 3,000 gamma-ray sources in the first three years of operation, representing a more than tenfold increase over current source counts.
• The P/L detector achieves a full-energy peak energy resolution of 5% at 1 MeV, enabling high-fidelity energy measurements critical for spectral analysis.
• The L/SCD tracker provides angular resolution of better than 3° FWHM at 100 MeV and energy resolution of 10% at 1 GeV, supporting precise source localization and spectral studies.
• Thermal simulations confirm that the radiator system can effectively dissipate 1.5 kW of heat, maintaining the P/L detector within the optimal temperature range of -10°C to 0°C.
• The propulsion system is designed with 266 kg of hydrazine, of which over 190 kg is allocated for controlled re-entry at the end of mission, ensuring compliance with space debris mitigation standards.
• The mission design supports three key pointing modes: zenith scanning, nearly inertial pointing for continuous source tracking, and fast repointing during eclipses (up to two per orbit), enabling full sky coverage and transient response.