The e-ASTROGAM gamma-ray space mission

Abstract

e-ASTROGAM is a gamma-ray space mission to be proposed as the M5 Medium-size mission of the European Space Agency. It is dedicated to the observation of the Universe with unprecedented sensitivity in the energy range 0.2 -100 MeV, extending up to GeV energies, together with a groundbreaking polarization capability. It is designed to substantially improve the COMPTEL and Fermi sensitivities in the MeV-GeV energy range and to open new windows of opportunity for astrophysical and fundamental physics space research. e-ASTROGAM will operate as an open astronomical observatory, with a core science focused on (1) the activity from extreme particle accelerators, including gamma-ray bursts and active galactic nuclei and the link of jet astrophysics to the new astronomy of gravitational waves, neutrinos, ultra-high energy cosmic rays, (2) the high-energy mysteries of the Galactic center and inner Galaxy, including the activity of the supermassive black hole, the Fermi Bubbles, the origin of the Galactic positrons, and the search for dark matter signatures in a new energy window; (3) nucleosynthesis and chemical evolution, including the life cycle of elements produced by supernovae in the Milky Way and the Local Group of galaxies. e-ASTROGAM will be ideal for the study of high-energy sources in general, including pulsars and pulsar wind nebulae, accreting neutron stars and black holes, novae, supernova remnants, and magnetars. And it will also provide important contributions to solar and terrestrial physics. The e-ASTROGAM telescope is optimized for the simultaneous detection of Compton and pair-producing gamma-ray events over a large spectral band. It is based on a very high technology readiness level for all subsystems and includes many innovative features for the detectors and associated electronics.

γ-ray telescopes using conversions to e+e− pairs: event generators, angular resolution and polarimetry

“…HARPO [13] with a gaseous detector, e-ASTROGAM [7] with a silicon tracker and even the Fermi-LAT [33]), and few generators take the photon polarisation into account. Besides our exact 5D generator, only G4:livermorepola tries to describe the angular asymmetry in the case of polarised photons.…”

“…Several technologies are being considered to improve the angular resolution such as silicon wafer stacks (i.e., without tungsten converters) [1,2,3,4,5,6,7], liquid noble-gas time projection chambers TPC (argon [8], or xenon [9]) and emulsions [10].…”

About cosmic gamma ray lines

“…The achieved spatial resolution is of order 2-3 degrees only, while spectral resolution, however, is sufficient for astrophysical detail studies from line shapes and centroid shifts for several lines and sources of interest [22]. Examples for proposed next-generation instruments [23,24] have demonstrated that about one order of magnitude improvements or more would be feasible, affordability assessment by the scientific funding communities set aside.…”

“…Diffuse nuclear-line and annihilation-line emission will be discussed thereafter, with respect to the underlying source populations. 44 Ti ccSN interior nucleosynthesis 0.078 radioactive decay: 44 Ti ccSN interior nucleosynthesis 0.122 radioactive decay: 57 Ni supernova nucleosynthesis 0.158 radioactive decay: 56 Ni supernova nucleosynthesis 0.478 radioactive decay: 7 Be nova nucleosynthesis 0.511 positron annihilation nucleosynthesis, compact stars, binaries 0.812 radioactive decay: 56 Ni supernova nucleosynthesis 0.847 radioactive decay: 56 Co supernova nucleosynthesis 1.157 radioactive decay: 44 Ti ccSN interior nucleosynthesis 1.173 radioactive decay: 60 Fe,Co ccSN ejected nucleosynthesis 1.238 radioactive decay: 56 Co supernova nucleosynthesis 1.275 radioactive decay: 22 Na nova nucleosynthesis 1.332 radioactive decay: 60 Fe,Co ccSN ejected nucleosynthesis 1.634 nuclear excitation: 20 Ne cosmic ray / ISM interactions 1.809 radioactive decay: 26 Al massive-star and ccSN nucleosynthesis 2.230 neutron capture by H energetic nucleon interactions 2.313 nuclear excitation: 14 N cosmic ray / ISM interactions 2.754 nuclear excitation: 24 Mg cosmic ray / ISM interactions 4.438 nuclear excitation: 12 C cosmic ray / ISM interactions 6.129 nuclear excitation: 16 O cosmic ray / ISM interactions…”

γ-Ray polarimetry with conversions to e+e− pairs: Polarization asymmetry and the way to measure it

“…For thick wafers (≈ 500 µm [47,48,49,50,51,52]), the effective polarization asymmetry, and therefore the dilution factor, are still low because multiple scattering remains an issue. It's only if very thin wafers can be made, held and launched (≈ 150 µm [53]) that there is some hope of a sizeable sensitivity to polarization (see Figs.…”