The e-ASTROGAM mission: Exploring the extreme Universe with gamma rays in the MeV – GeV range

TLDR: The e-ASTROGAM (enhanced ASTROGAM) project as mentioned in this paper 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.

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, albeit with rapidly degrading angular resolution, 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 the promise of eLISA.

Figures

FIG. 3. Compilation of the measurements of the total extragalactic gamma-ray intensity between 1 keV and 820 GeV [13], with different components from current models; the contribution from MeV blazars is largely unknown. The semitransparent band indicates the energy region in which eASTROGAM will dramatically improve on present knowledge.

FIG. 2. An example of the capability of e-ASTROGAM to transform our knowledge of the MeV-GeV sky. Upper panel: The upper left figure shows the 1-30 MeV sky as observed by COMPTEL in the 1990s; the lower right figure shows the simulated Cygnus region in the 1-30 MeV energy region from e-ASTROGAM. Lower panel: comparison between the view of the Cygnus region by Fermi in 8 years (left) and that by e-ASTROGAM in one year of effective exposure (right) between 400 MeV and 800 MeV.

FIG. 8. Imaging the inner Galaxy region: simulated performance of e-ASTROGAM in one year of effective exposure (right panels) compared to 8 years of Fermi (left panels) for the energy ranges 150 MeV - 400 MeV (top) and 400 MeV - 800 MeV (bottom).

FIG. 15. Exploded view drawing of a elementary module of the Calorimeter with its alveolus structure.

FIG. 16. Expected data flow of the on-board e-ASTROGAM gamma-ray data acquisition system.

FIG. 12. Representative topologies for a Compton event (left) and for a pair event (right). Photon tracks are shown in pale blue, dashed, and electron and/or positron tracks in red, solid. From [96].

Full text

The e-ASTROGAM mission
(exploring the extreme Universe with gamma rays in the MeV – GeV range)
Alessandro De Angelis,
1, 2, 3, 4, ∗
Vincent Tatischeff,
5, ∗
Marco Tavani,
6, 7, 8
Uwe Oberlack,
9
Isabelle A. Grenier,
10
Lorraine Hanlon,
11
Roland Walter,
12
Andrea Argan,
13
Peter von Ballmoos,
14
Andrea Bulgarelli,
15
Immacolata Donnarumma,
6, 16
Margarita Hernanz,
17
Irfan Kuvvetli,
18
Mark Pearce,
19
Andrzej Zdziarski,
20
Alessio Aboudan,
21
Marco Ajello,
22
Giovanni Ambrosi,
23
Denis Bernard,
24
Elisa Bernardini,
25
Valter Bonvicini,
26
Andrea Brogna,
24
Marica Branchesi,
27, 28
Carl Budtz-Jørgensen,
18
Andrei Bykov,
29
Riccardo Campana,
15
Martina Cardillo,
6
Paolo Coppi,
30
Domitilla De Martino,
31
Roland Diehl,
32
Michele Doro,
1, 33
Valentina Fioretti,
15
Stefan Funk,
34
Gabriele Ghisellini,
35
J. Eric Grove,
36
Clarisse Hamadache,
37, 38, 39
Dieter H. Hartmann,
22
Masaaki Hayashida,
40
Jordi Isern,
17
Gottfried Kanbach,
41
J¨urgen Kiener,
37, 38, 39
J¨urgen Kn¨odlseder,
42
Claudio Labanti,
15
Philippe Laurent,
43
Olivier Limousin,
44
Francesco Longo,
45, 46
Karl Mannheim,
47
Martino Marisaldi,
48, 15
Manel Martinez,
49
Mario N. Mazziotta,
50
Julie McEnery,
51
Sandro Mereghetti,
52
Gabriele Minervini,
6
Alexander Moiseev,
53
Aldo Morselli,
8
Kazuhiro Nakazawa,
54
Piotr Orleanski,
55
Josep M. Paredes,
56
Barbara Patricelli,
57, 58
Jean Peyr´e,
37, 38, 39
Giovanni Piano,
6
Martin Pohl,
59
Harald Ramarijaona,
37, 38, 39
Riccardo Rando,
1, 33
Ignasi Reichardt,
60
Marco Roncadelli,
61, 62
Rui Curado da Silva,
63
Fabrizio Tavecchio,
35
David J. Thompson,
64
Roberto Turolla,
65, 66
Alexei Ulyanov,
67
Andrea Vacchi,
68
Xin Wu,
69
and Andreas Zoglauer
70
(On behalf of the e-ASTROGAM Collaboration)
1
Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy
2
Istituto Nazionale di Astrofisica, Padova, Italy
3
Dipartimento di Matematica, Informatica e Fisica, Universit`a di Udine, I-33100 Udine, Italy
4
Laboratorio de Instrumenta¸cao e Particulas and Instituto Superior Tecnico, Lisboa, Portugal
5
CSNSM, CNRS and University of Paris Sud, F-91405, Orsay, France
6
INAF/IAPS, via del Fosso del Cavaliere 100, I-00133, Roma, Italy
7
University of Roma “Tor Vergata”, I-00133, Roma, Italy
8
Istituto Nazionale di Fisica Nucleare, Sezione di Roma “Tor Vergata”, I-00133 Roma, Italy
9
Institute of Physics and PRISMA Excellence Cluster,
Johannes Gutenberg University Mainz, D-55099 Mainz, Germany
10
AIM Paris-Saclay, CEA/IRFU, CNRS, Univ Paris Diderot, F-91191 Gif-sur-Yvette, France
11
School of Physics, University College Dublin, Ireland
12
University of Geneva, Chemin d’Ecogia 16, CH-1290 Versoix, Switzerland
13
INAF Headquarters, Viale del Parco Mellini, 84, I-00136, Roma, Italy
14
IRAP Toulouse, 9 av. du Colonel-Roche - BP 44 346, F-31028 Toulouse Cedex 4, France
15
INAF/IASF Bologna, Via Gobetti 101, I-40129 Bologna, Italy
16
Now at Agenzia Spaziale Italiana, Roma, Italy
17
ICE (CSIC-IEEC), Campus UAB, Carrer Can Magrans s/n,
E-08193 Cerdanyola del Valles, Barcelona, Spain
18
DTU Space, National Space Institute, Technical University of Denmark, Kgs. Lyngby, Denmark
19
KTH Royal Institute of Technology, Dept. of Physics, 10691 Stockholm, Sweden
20
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, PL-00-716 Warszawa, Poland
21
Dept. of Physics and Astronomy University of Padova and INAF, via Marzolo 8, I-35131 Padova, Italy
22
Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, USA
23
INFN Perugia, Perugia, Italy
24
Institute of Physics and PRISMA Excellence Cluster,
Johannes Gutenberg University Mainz, 55099 Mainz, Germany
25
DESY, Platanen Allee 6, D-15738 Zeuthen, Germany
26
INFN Trieste, via A. Valerio, I-34127 Trieste, Italy
27
Universit`a degli Studi di Urbino, DiSPeA, I-61029 Urbino, Italy
28
Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, Italy
29
Ioffe Institute, St.Petersburg 194021, Russia
30
Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101, USA
31
NAF - Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli, Italy
32
Max Planck Institut fuer extraterrestrische Physik, Giessenbachstr.1,
D-85748 Garching, Germany; Excellence Cluster Universe, Germany
33
Dipartimento di Fisica e Astronomia “G. Galilei”, Universit`a di Padova, I-35131 Padova, Italy
34
Erlangen Centre for Astroparticle Physics, D-91058 Erlangen, Germany
35
INAF - Osservatorio di Brera, via E. Bianchi 46, I-23807 Merate, Italy
36
U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375, USA
37
CSNSM, F-91405 Orsay Campus, France
arXiv:1611.02232v5 [astro-ph.HE] 4 Jun 2017

2
38
IN2P3-CNRS/Univ. Paris-Sud, F-91405 Orsay Campus, France
39
Universit´e Paris-Saclay, F-91405 Orsay Campus, France
40
Institute for Cosmic Ray Research, the University of Tokyo, Kashiwa, Chiba, 277-8582, Japan
41
Max-Planck-Institut fur Extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
42
IRAP Toulouse, 9 av. du Colonel-Roche - BP 44 346, 31028 Toulouse Cedex 4, France
43
PC, Univ Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris,
10 rue Alice Domont et L´eonie Duquet, F-75205 Paris Cedex 13, France
44
CEA/Saclay IRFU/Department of Astrophysics, Bat. 709, F-91191, Gif-Sur-Yvette, France
45
Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste, Italy
46
Dipartimento di Fisica, Universit`a di Trieste, I-34127 Trieste, Italy
47
Universitaet Wuerzburg, Campus Hubland Nord, Lehrstuhl fuer Astronomie,
Emil-Fischer-Strasse 31, D-97074 Wuerzburg, Germany
48
University of Bergen, Norway
49
IFAE-BIST, Edifici Cn. Universitat Autonoma de Barcelona, E-08193 Bellaterra, Spain
50
Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari, Italy
51
NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
52
INAF/IASF, Via Bassini 15, I-20133 Milano, Italy
53
CRESST/NASA/GSFC and University of Maryland, College Park, USA
54
Department of Physics, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033
55
Space Research Center of Polish Academy of Sciences, Bartycka 18a, PL-00-716 Warszawa, Poland
56
Departament de Fisica Quantica i Astrofisica, ICCUB, Universitat de Barcelona,
IEEC-UB, Marti i Franques 1, E-08028 Barcelona, Spain
57
Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
58
Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
59
Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany
60
Universitat Rovira i Virgili, Carrer de l‘Escorxador, E-43003 Tarragona, Spain
61
INFN Pavia, via A. Bassi 6, I-27100 Pavia, Italy
62
INAF Milano, Milano, Italy
63
LIP, Departamento de Fsica Universidade de Coimbra, P-3004-516 Coimbra, Portugal
64
NASA Goddard Space Flight Center, Greenbelt, MD, USA
65
Dept. of Physics and Astronomy University of Padova, via Marzolo 8, I-35131 Padova, Italy
66
University College London, United Kingdom
67
School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
68
University of Udine and INFN GC di Udine, via delle Scienze, I-33100 Udine, Italy
69
University of Geneva, Department of Nuclear and Particle Physics,
24 quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland
70
University of California at Berkeley, Space Sciences Laboratory, 7 Gauss Way, Berkeley, CA 94720, USA
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, albeit with rapidly degrading angular
resolution, 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 res-
olution, 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 gen-
eration 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 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
PACS numbers: PACS 95.55 Ka, PACS 98.70 Rz, 26.30.-k
∗
Corresponding Author

3
CONTENTS
I. Introduction 3
II. Science Case 4
A. Processes at the heart of the extreme
Universe: prospects for the Astronomy of the
2030s 5
1. Gamma-Ray Bursts 8
2. e-ASTROGAM and the new Astronomy 8
B. The origin and impact of high-energy
particles on Galaxy evolution, from cosmic
rays to antimatter 9
1. What are the CR energy distributions
produced inside SNRs and injected into the
surrounding ISM? 9
2. How do CR fluxes vary with Galactic
environments, from passive interstellar
clouds to active starburst regions and near
the Galactic Center? 10
3. Where are the low-energy CRs and how do
they penetrate dense clouds? 10
4. The origin and energy content of Galactic
wind and Fermi bubbles 11
5. Antimatter and WIMP Dark Matter 12
C. Nucleosynthesis and the chemical evolution of
our Galaxy 13
1. What are the progenitor system(s) and
explosion mechanism(s) of thermonuclear
SNe? Can we use SN Ia for precision
cosmology? 13
2. How do core-collapse supernovae (CCSNe)
explode? What is the recent history of
CCSNe in the Milky Way? 14
3. Nova explosions 15
4. How are cosmic isotopes created in stars
and distributed in the interstellar
medium? 15
D. Observatory science in the MeV - GeV
domain 16
III. Scientific Requirements 17
IV. The Scientific Instrument 20
A. Measurement principle and payload
overview 20
1. Silicon Tracker 21
2. Calorimeter 22
3. Anticoincidence System 24
4. Data Handling and Power Supply 25
5. Trigger logic and data flow architecture 26
B. Performance assessment 26
1. Background model 27
2. Angular and spectral resolution 27
3. Field of View 28
4. Effective area and continuum sensitivity 28
5. Line sensitivity 28
6. Polarization response 29
C. Technology readiness 31
V. Mission Configuration and Profile 31
A. Orbit and launcher 31
B. Spacecraft and system requirements 31
1. Attitude and Orbital Control Systems 32
2. Thermal control system 33
VI. Summary 33
Acknowledgments 33
References 33
I. INTRODUCTION
e-ASTROGAM is a gamma-ray mission concept pro-
posed as a response to the European Space Agency (ESA)
Call for the fifth Medium-size mission (M5) of the Cosmic
Vision Science Programme. The planned launch date is
2029.
The main constituents of the e-ASTROGAM payload
will be:
• A Tracker in which the cosmic γ-rays can undergo
a Compton scattering or a pair conversion, based
on 56 planes of double-sided Si strip detectors, each
plane with total area of ∼1 m
2
;
• A Calorimeter to measure the energy of the sec-
ondary particles, made of an array of CsI (Tl) bars
of 5×5×80 mm
3
each, with relative energy resolu-
tion of 4.5% at 662 keV;
• An Anticoincidence system (AC), composed of
a standard plastic scintillator AC shielding and a
Time of Flight, to veto the charged particle back-
ground.
If selected, e-ASTROGAM will operate in a maturing
gravitational wave and multimessenger epoch, opening
up entirely new and exciting synergies. The mission will
provide unique and complementary data of significant in-
terest to a broad astronomical community, in a decade
of powerful observatories such as LIGO-Virgo-GEO600-
KAGRA, SKA, ALMA, E-ELT, LSST, JWST, Athena,
CTA and the promise of eLISA.
The core mission science of e-ASTROGAM addresses
three major topics of modern astrophysics.
• Processes at the heart of the extreme Uni-
verse: prospects for the Astronomy of the
2030s
Observations of relativistic jet and outflow sources
(both in our Galaxy and in active galactic nuclei,
AGNs) in the X-ray and GeV–TeV energy ranges
have shown that the MeV–GeV band holds the
key to understanding the transition from the low
energy continuum to a spectral range shaped by

4
very poorly understood particle acceleration pro-
cesses. e-ASTROGAM will: (1) determine the
composition (hadronic or leptonic) of the outflows
and jets, which strongly influences the environment
– breakthrough polarimetric capability and spec-
troscopy providing the keys to unlocking this long-
standing question; (2) identify the physical acceler-
ation processes in these outflows and jets (e.g. dif-
fusive shocks, magnetic field reconnection, plasma
effects), that may lead to dramatically different
particle energy distributions; (3) clarify the role
of the magnetic field in powering ultrarelativistic
jets in gamma-ray bursts (GRBs), through time-
resolved polarimetry and spectroscopy. In addition,
measurements in the e-ASTROGAM energy band
will have a big impact on multimessenger astron-
omy in the 2030s. Joint detection of gravitational
waves and gamma-ray transients would be ground-
breaking.
• The origin and impact of high-energy parti-
cles on galaxy evolution, from cosmic rays
to antimatter
e-ASTROGAM will resolve the outstanding issue
of the origin and propagation of low-energy cos-
mic rays affecting star formation. It will measure
cosmic-ray diffusion in interstellar clouds and their
impact on gas dynamics and state; it will provide
crucial diagnostics about the wind outflows and
their feedback on the Galactic environment (e.g.,
Fermi bubbles, Cygnus cocoon). e-ASTROGAM
will have optimal sensitivity and energy resolution
to detect line emissions from 511 keV up to 10 MeV,
and a variety of issues will be resolved, in particu-
lar: (1) origin of the gamma-ray and positron ex-
cesses toward the Galactic inner regions; (2) deter-
mination of the astrophysical sources of the local
positron population from a very sensitive observa-
tion of pulsars and supernova remnants (SNRs). As
a consequence e-ASTROGAM will be able to dis-
criminate the backgrounds to dark matter (DM)
signals.
• Nucleosynthesis and the chemical enrich-
ment of our Galaxy
The e-ASTROGAM line sensitivity is more than
an order of magnitude better than previous instru-
ments. The deep exposure of the Galactic plane
region will determine how different isotopes are
created in stars and distributed in the interstellar
medium; it will also unveil the recent history of su-
pernova explosions in the Milky Way. Furthermore,
e-ASTROGAM will detect a significant number of
Galactic novae and supernovae in nearby galaxies,
thus addressing fundamental issues in the explosion
mechanisms of both core-collapse and thermonu-
clear supernovae. The γ-ray data will provide a
much better understanding of Type Ia supernovae
and their evolution with look-back time and metal-
licity, which is a pre-requisite for their use as stan-
dard candles for precision cosmology.
In addition to addressing its core scientific goals, e-
ASTROGAM will achieve many serendipitous discover-
ies (the unknown unknowns) through its combination
of wide field of view (FoV) and improved sensitivity,
measuring in 3 years the spectral energy distributions
of thousands of Galactic and extragalactic sources, and
providing new information on solar flares and terrestrial
gamma-ray flashes (TGF). e-ASTROGAM will become a
key contributor to multiwavelength time-domain astron-
omy. The mission has outstanding discovery potential
as an Observatory facility that is open to a wide astro-
nomical community.
e-ASTROGAM is designed to achieve:
• Broad energy coverage (0.3 MeV to 3 GeV), with
one-two orders of magnitude improvement in con-
tinuum sensitivity in the range 0.3 MeV – 100 MeV
compared to previous instruments (the lower en-
ergy limit can be pushed to energies as low as 150
keV, albeit with rapidly degrading angular resolu-
tion, for the tracker, and to 30 keV for calorimetric
detection);
• Unprecedented performance for γ-ray lines, with,
for example, a sensitivity for the 847 keV line from
Type Ia SNe 70 times better than that of INTE-
GRAL/SPI;
• Large FoV (>2.5 sr), ideal to detect transient
sources and hundreds of GRBs;
• Pioneering polarimetric capability for both steady
and transient sources;
• Optimized source identification capability afforded
by the best angular resolution achievable by state-
of-the-art detectors in this energy range (about 0.15
degrees at 1 GeV);
• Sub-millisecond trigger and alert capability for
GRBs and other cosmic and terrestrial transients;
• Combination of Compton and pair-production
detection techniques allowing model-independent
control on the detector systematic uncertainties.
II. SCIENCE CASE
e-ASTROGAM will open the MeV region for explo-
ration, with an improvement of one-two orders of magni-
tude in sensitivity (Fig. 1) compared to the current state
of the art, much of which was derived from the COMP-
TEL instrument more than two decades ago. It will also
achieve a spectacular improvement in terms of source lo-
calization accuracy (Fig. 2) and energy resolution, and
will allow to measure the contribution to the radiation
of the Universe in an unknown range (Fig. 3). The sen-
sitivity of e-ASTROGAM will reveal the transition from

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10
10
e-ASTROGAM
SPI
IBIS-ISGRI
IBIS-PICsIT
JEM-X
COMPTEL
EGRET
CTA North
CTA South
Fermi-LAT
LHAASO
HiSCORE
MAGIC
VERITAS
HAWC
Energy (MeV)
Sensitivity (erg cm
-2
s
-1
)
FIG. 1. Point source continuum differential sensitivity of different X- and γ-ray instruments. The curves for INTEGRAL/JEM-
X, IBIS (ISGRI and PICsIT), and SPI are for an effective observation time T
obs
= 1 Ms. The COMPTEL and EGRET
sensitivities are given for the typical observation time accumulated during the ∼9 years of the CGRO mission (see Fig. 1 in
[129]). The Fermi/LAT sensitivity is for a high Galactic latitude source in 10 years of observation in survey mode. For MAGIC,
VERITAS (sensitivity of H.E.S.S. is similar), and CTA, the sensitivities are given for T
obs
= 50 hours. For HAWC T
obs
= 5 yr,
for LHAASO T
obs
= 1 yr, and for HiSCORE T
obs
= 1000 h. The e-ASTROGAM sensitivity is calculated at 3σ for an effective
exposure of 1 year and for a source at high Galactic latitude.
nuclear processes to those involving electro- and hydro-
dynamical, magnetic and gravitational interactions.
An important characteristic of e-ASTROGAM is its
ability to measure polarization in the MeV range, which
is afforded by Compton interactions in the detector. Po-
larization encodes information about the geometry of
magnetic fields and adds a new observational pillar, in
addition to the temporal and spectral, through which
fundamental processes governing the MeV emission can
be determined. The addition of polarimetric information
will be crucial for a variety of investigations, including
accreting black-hole (BH) systems, magnetic field struc-
tures in jets, and the emission mechanisms of GRBs. Po-
larization will provide definitive insight into the presence
of hadrons in extragalactic jets and the origin of ultra-
high-energy cosmic rays (CR).
In the following sections, the core science questions [50]
to be addressed by e-ASTROGAM are presented. The
requirements coming from the scientific objectives, and
driving the instrument design, are presented in Sect. III.
A. Processes at the heart of the extreme Universe:
prospects for the Astronomy of the 2030s
The Universe accessible to e-ASTROGAM is domi-
nated by strong particle acceleration. Ejection of plasma
(jets or uncollimated outflows), ubiquitous in accreting
systems, drives the transition from the keV energy range,
typical of the accretion regime, to the GeV-TeV range,
through reprocessing of synchrotron radiation (e.g, in-
verse Compton, IC) or hadronic mechanisms. For some
sources the MeV band naturally separates the accelera-
tion and reprocessing energy ranges. Other systems, in-
stead, radiate the bulk of their output in the MeV band.
This is the most frequent case for AGNs at cosmological
distances.
e-ASTROGAM will also study extreme acceleration
mechanisms from compact objects such as neutron stars
and (supermassive) black holes. Its polarimetric capabil-
ities and its continuum sensitivity will solve the problem
of the nature of the highest energy radiation.
The transition to non-thermal processes involves, in
particular, the emission of relativistic jets and winds. In
our Galaxy, this is relevant for compact binaries and mi-
croquasars. The interplay between accretion processes
and jet emission can best be studied in the MeV region,
where disk Comptonization is expected to fade and other
non-thermal components can originate from jet parti-
cles. e-ASTROGAM observations of Galactic compact
objects and in particular of accreting BH systems (such
as Cygnus X-1 [151], Cygnus X-3 ([3, 133]), V404 Cygni
[119]) will determine the nature of the steady-state emis-
sion due to Comptonization and the transitions to highly
non-thermal radiation (Fig. 4). The main processes be-
hind this emission are Compton scattering by accelerated
non-thermal electrons and its attenuation/reprocessing
by electron-positron pair production. The magnetic field
in the BH vicinity can be quite strong, and have both
random and ordered components; synchrotron emission

Frequently asked questions

Q1. What are the contributions in "The e-astrogam mission (exploring the extreme universe with gamma rays in the mev – gev range)" ?

Alessandro De Angelis, 2, 3, 4 ∗ Vincent Tatischeff, ∗ Marco Tavani, 7, 8 Uwe Oberlack, Isabelle A. Grenier, Lorraine Hanlon, Roland Walter, Andrea Argan, Peter von Ballmoos, Andrea Bulgarelli, Immacolata Donnarumma, 16 Margarita Hernanz, Irfan Kuvvetli, Mark Pearce, Andrzej Zdziarski, Alessio Aboudan, Marco Ajello, Giovanni Ambrosi, Denis 

Q2. What are the main processes behind the emission of a blazar?

The main processes behind this emission are Compton scattering by accelerated non-thermal electrons and its attenuation/reprocessing by electron-positron pair production. 

Q3. What is the role of relativistic particles in the evolution of galaxies?

Relativistic particles permeate the interstellar medium (ISM) of galaxies and drive their evolution by providing heat, pressure and ionization to the clouds and to galactic winds and outflows. 

Q4. What is the difficult thing to constrain through observations?

The cooling down of hot nucleosynthesis ejecta and their trajectories towards new star formation are particularly hard to constrain through observations. 

Q5. What is the sensitivity of e-ASTROGAM for detection of DM?

In final states characterized by a photon continuum or by γ-ray lines, the e-ASTROGAM sensitivity for the detection of DM is complementary to Fermi and CTA because it covers with larger sensitivity the low-mass interval. 

Q6. What are the main functions related to the scientific data processing?

The main functions related to the scientific data processing are: (i) BEE interfacing through dedicated links to acquire the scientific data; (ii) the real-time software processing of the collected silicon Tracker, Anticoincidence and Calorimeter scientific data aimed at rejecting background events to meet the telemetry requirements; (iii) scientific data compression; (iv) formatting of the compressed data into telemetry26packets. 

Q7. How much is the payload required to fulfill the mission needs?

From a preliminary estimation of the propellant budget the amount of hydrazine required to fulfill the mission needs are about 266 kg, among which more than 190 kg are allocated to the end of mission disposal. 

Q8. What can be done to reduce the astrophysical background uncertainties?

a large class of spectral features in the MeV-GeV range can result in indications for WIMP DM particles, or significantly reduce the astrophysical background uncertainties to identify genuine DM signatures in VHE photon spectra [38]. 

Q9. What is the importance of resolving the diffuse pion emission produced in the remnants?

Resolving the diffuse pion emission produced in those clouds against the bright Galactic background is essential to probe the CR spectra that are actually injected into the ISM. 

Q10. What are the two bases that can be used as mission ground stations?

bothESA and ASI have satellite communication bases near the equator (Kourou and Malindi) that can be efficiently used as mission ground stations. 

Q11. What is the way to identify a hadronic scenario?

Even in non optimal conditions (fields not well ordered, alignment to line of sight not optimal) the polarization signature would allow to identify unambiguously a hadronic scenario. 

Q12. How many s of background is required to save the events?

A cyclic buffer is required to routinely save the events; the size of this buffer is defined in order to store 100 s of background. 

Q13. What can be done to disentangle the contributions from the diffuse background?

Finally an improved angular resolution with respect to AGILE and Fermi -LAT in the inner Galaxy region and in regions closer to Earth in the 5 MeV–100 MeV energy range can disentangle the possible contributions from the diffuse background, from point sources, and other possible emitters. 

Q14. How can the authors detect the origin of photons?

The origin of photons can be effectively probed both by much improved spectral measurements in the MeV-GeV band (detecting the “pion bump”), and by polarimetric observations. 

Q15. How can the photon be absorbed in the Calorimeter?

The scattered photon can be absorbed in the Calorimeter or (with smaller probability) scattered a second time in the Tracker before being absorbed in the Calorimeter where its energy and absorption position are measured. 

Q16. What is the way to capture the radiation from decaying pions?

Note also that e-ASTROGAM’s energy coverage is ideally suited (compared to Fermi) to capture the radiation from decaying pions and anti-proton annihilation,especially if the relevant sources are cosmological and redshifted. 

Q17. What is the way to understand the evolution of SNe?

Although useful up to now, in view of the development of precision cosmology, a better, astrophysically supported understanding of thermonuclear SNe, as well as their evolutionary effects at large distances and low metallicities, are mandatory. 

Q18. What is the evidence for the emergence of a Galactic wind?

There is increasing evidence, observationally (e.g. [47, 87]) and theoretically, for the emergence from the inner 200 pc of the Galaxy of a Galactic wind flowing to large height (∼ 10 kpc) into the halo and partly accelerated by the pressure gradient supplied by CRs [37, 57].