newASTROGAM: Advanced Gamma-Ray Observatory

• newASTROGAM is a proposed space-based gamma-ray observatory designed to bridge the MeV sensitivity gap using silicon tracking, crystal calorimetry, and a coded mask.
• It employs innovative detection methods—photoelectric, Compton, and pair-production—to achieve high-resolution spectroscopy, imaging, timing, and polarimetry.
• The mission concept targets rapid all-sky surveys and transient alerts, enabling multi-messenger studies of compact objects, nucleosynthesis, cosmic rays, and dark matter.

Searching arXiv for recent and foundational papers on newASTROGAM and predecessor ASTROGAM concepts. newASTROGAM is a proposed space-based gamma-ray observatory for the study of the non-thermal Universe from hard X-rays to GeV energies. In its 2025 formulation, it is described as a mission concept covering 15 keV to 3 GeV, combining a Silicon tracker, a crystal calorimeter, an anti-coincidence detector, and a thin X-ray coded mask, so that photons can be detected through the photoelectric effect, Compton scattering, and electron-positron pair production (Berge et al., 10 Jul 2025). It extends the ASTROGAM mission lineage developed in earlier e-ASTROGAM and ASTRO-MEV studies, which were designed to address the long-standing sensitivity gap in the MeV domain, to provide spectroscopy, imaging, timing, and polarimetry, and to connect gamma-ray astrophysics with gravitational-wave, neutrino, and broader multi-messenger programs (Tatischeff et al., 2016, Angelis et al., 2016, Angelis et al., 2021).

1. Nomenclature, lineage, and mission concept

The designation “newASTROGAM” belongs to a sequence of closely related mission concepts rather than to an already flown observatory. The earlier e-ASTROGAM proposal was formulated as an ESA M5 Medium-size mission dedicated to the observation of the Universe with unprecedented sensitivity in the energy range 0.2–100 MeV, extending up to GeV energies, and later as an observatory covering 0.15 MeV–3 GeV or 0.3 MeV–3 GeV depending on the instrument threshold convention adopted in a given design study (Tatischeff et al., 2016, Tatischeff et al., 2017, Angelis et al., 2017). The 2021 ASTRO-MEV concept preserved the same basic scientific rationale for an M-class MeV mission, emphasizing the 0.1 MeV–1 GeV interval and the role of a silicon hodoscope, 3D position-sensitive calorimeter, and anticoincidence system (Angelis et al., 2021). The 2025 newASTROGAM paper then reframed the concept for the ESA M8 call, widening the nominal band to 15 keV–3 GeV through the addition of a thin coded-mask imager (Berge et al., 10 Jul 2025).

A distinct but related branch is All-Sky-ASTROGAM, proposed as an ESA “Fast” mission with a nearly $4\pi$ sr field of view, an L2 orbit, and strong emphasis on all-sky transient monitoring from 100 keV to $\sim 1$ GeV (Tatischeff et al., 2019). It is not identical to the low-inclination low-Earth-orbit ASTROGAM line. This suggests that the ASTROGAM literature should be read as a family of mission architectures sharing common detector principles and MeV-science drivers, but optimized differently for successive agency calls and observing strategies.

The common programmatic objective across these studies is the closure of the “MeV gap”: the region between hard-X-ray instruments and GeV pair-conversion telescopes where past coverage was limited by comparatively poor sensitivity, angular resolution, or line sensitivity. The recurring mission argument is that this band carries unique diagnostics of non-thermal particle populations, radioactive isotopes, positron annihilation, low-energy cosmic rays, and polarization signatures of relativistic outflows (Tatischeff et al., 2016, Angelis et al., 2017).

2. Scientific rationale and astrophysical scope

The 2025 newASTROGAM concept organizes its science case around compact objects and relativistic outflows, merger events and gamma-ray bursts, supernova nucleosynthesis and chemical evolution, cosmic-ray sources and feedback, and dark matter and fundamental physics (Berge et al., 10 Jul 2025). Earlier e-ASTROGAM documents group similar motivations into three pillars: extreme particle accelerators and multi-messenger connections; the Galactic center, Fermi Bubbles, positrons, and dark matter; and nucleosynthesis and chemical evolution (Tatischeff et al., 2016).

In the domain of compact objects and jets, the mission family is intended to address how and where particles are accelerated to MeV–GeV energies in pulsars, magnetars, black-hole X-ray binaries, active galactic nuclei, gamma-ray bursts, microquasars, and pulsar wind nebulae. The central diagnostics are broadband spectroscopy, time variability, and polarimetry, particularly for distinguishing leptonic from hadronic emission channels, diagnosing jet magnetization, and identifying emission sites in relativistic outflows (Berge et al., 10 Jul 2025, Tatischeff et al., 2017).

For merger events and transient astronomy, the science case centers on prompt and afterglow emission from short and long GRBs and on their connection to binary neutron-star and neutron-star–black-hole mergers. Across the ASTROGAM literature, wide field of view, submillisecond or subsecond triggering, and rapid localization are repeatedly emphasized as prerequisites for joint observations with gravitational-wave interferometers and neutrino telescopes (Tatischeff et al., 2016, Tatischeff et al., 2019, Berge et al., 10 Jul 2025).

The nuclear-astrophysics program is equally central. The observatory line is designed to measure gamma-ray lines from radioactive isotopes such as $^{56}$Co, $^{44}$Ti, $^{26}$Al, $^{22}$Na, and the 511 keV positron-annihilation line, and thereby constrain Type Ia and core-collapse supernova progenitors, ejecta composition, explosion asymmetries, and the life cycle of freshly synthesized elements in the interstellar medium (Tatischeff et al., 2016, Angelis et al., 2017). The 2025 newASTROGAM formulation extends this to kilonovae and the contribution of mergers and novae to $r$- and $p$-process abundances (Berge et al., 10 Jul 2025).

The cosmic-ray and Galactic-ecology program focuses on the spectrum of fresh versus reaccelerated cosmic rays below $\sim 500$ MeV, the separation of hadronic $\pi^0$-decay signatures from bremsstrahlung and inverse-Compton emission, the mapping of nuclear de-excitation lines such as the 4.44 MeV $\sim 1$0C line, and the study of structures such as the Fermi Bubbles and the Galactic-center region (Tatischeff et al., 2016, Tatischeff et al., 2017, Angelis et al., 2021). The same band is also repeatedly identified as favorable for searches for sub-GeV dark matter, light dark-matter annihilation features, MeV-scale internal bremsstrahlung, axion-like particles, Lorentz-invariance-violation tests via GRB polarimetry, and explanations of the 511 keV line or Galactic-center MeV excess (Tatischeff et al., 2016, Roncadelli et al., 2017, Berge et al., 10 Jul 2025).

3. Payload architecture and detection principles

The 2025 payload concept is a single instrument surrounded by an anti-coincidence shield and augmented by a thin X-ray coded mask. The detector chain is designed so that hard X-rays can be imaged in the photoelectric regime, MeV photons can be reconstructed via Compton kinematics, and higher-energy events can be analyzed through pair production (Berge et al., 10 Jul 2025).

Subsystem	Configuration in the newASTROGAM concept	Primary role
Anti-coincidence shield	Plastic scintillator panels on top and four sides; segmented; rejection efficiency $\sim 1$1	Charged-particle veto
Thin X-ray coded mask	Tungsten sheet, pseudo-random pattern, open fraction $\sim 1$2, mask-to-detector distance $\sim 1$3 cm, half-coded FoV $\sim 1$4 sr	15–40 keV imaging and transient localization
Silicon Tracker	56 layers of double-sided silicon microstrip detectors with $\sim 1$5 cm ladders, strip pitch $\sim 1$6m, total thickness $\sim 1$7	Compton-electron and $\sim 1$8 tracking
Calorimeter	$\sim 1$9 cm CsI(Tl) or similar scintillator bars, dual-ended readout by silicon drift detectors or SiPMs	3D energy deposition and total-energy measurement

In the photoelectric regime, hard X-rays pass through the coded mask and convert in the first Tracker layers. In the Compton regime, given in the 2025 text as $^{56}$0 keV $^{56}$1 MeV, the incoming photon scatters in the Tracker and the scattered photon is absorbed in the calorimeter. The opening angle of the Compton cone is reconstructed from deposited energies $^{56}$2 and $^{56}$3 as

$^{56}$4

This regime also carries the azimuthal modulation used for linear polarimetry (Berge et al., 10 Jul 2025).

The predecessor e-ASTROGAM papers formulate the same principle with equivalent Compton kinematics and a detector optimized for simultaneous Compton and pair-event reconstruction. For pair production, above $^{56}$5 MeV, the incoming gamma ray converts to an $^{56}$6 pair in the silicon Tracker; the tracks determine the incident direction, and the azimuthal orientation of the pair plane carries polarization information (Tatischeff et al., 2016, Angelis et al., 2016, Tatischeff et al., 2017).

The 2025 addition of a coded mask is the most visible architectural change relative to earlier e-ASTROGAM designs. The mask provides angular resolution $^{56}$7 and localization $^{56}$8 a few arcmin for bright transients in the 15–40 keV range (Berge et al., 10 Jul 2025). This extends the observatory’s functionality below the classic MeV focus of the earlier designs, which already allowed tracker thresholds down to $^{56}$9 keV and calorimetric burst detection down to 30 keV (Angelis et al., 2016, Angelis et al., 2017).

4. Performance envelope and observing strategy

In its 2025 form, newASTROGAM is described as an all-sky-per-day survey mission with FoV $^{44}$0 sky and sub-hour to sub-day latency for arcminute localizations. The mission profile specifies an equatorial low-Earth orbit with inclination $^{44}$1 and altitude 550–600 km, all-sky survey mode with full-sky coverage in $^{44}$2 day, rapid transient alerts in $^{44}$3 minutes, a Target-of-Opportunity mode with inertial pointing capability, and a nominal lifetime of 3 years with a goal $^{44}$4 years (Berge et al., 10 Jul 2025).

The same low-inclination LEO strategy had already been adopted in earlier e-ASTROGAM studies because it minimizes South Atlantic Anomaly passages and trapped-particle backgrounds. In those studies, the combination of anticoincidence veto, event selections, and orbit choice yields a background environment limited largely by cosmic diffuse and atmospheric gamma rays rather than by detector-induced charged-particle contamination (Tatischeff et al., 2016, Angelis et al., 2021).

The published 2025 sensitivity summary states that, for a point source in $^{44}$5 s, newASTROGAM covers 15 keV–3 GeV and in the 0.3–30 MeV band is $^{44}$6–$^{44}$7 more sensitive than COMPTEL/INTEGRAL, with $^{44}$8 MeV cm$^{44}$9 s$^{26}$0 at 1 MeV and $^{26}$1 erg cm$^{26}$2 s$^{26}$3 at 100 MeV (Berge et al., 10 Jul 2025). The same source gives nominal angular and energy performance of $^{26}$4 at 1 MeV, improving to $^{26}$5 at 10 MeV, $^{26}$6 at 100 MeV, and $^{26}$7 at 1 GeV, with $^{26}$8 at 100 keV, $^{26}$9 at 1 MeV, and $^{22}$0 at 100 MeV (Berge et al., 10 Jul 2025).

Earlier e-ASTROGAM studies provide a more explicit performance heritage. One 2016 design reports effective area values of 208 cm$^{22}$1 at 0.3 MeV, $^{22}$2 cm$^{22}$3 at 1 MeV, $^{22}$4 cm$^{22}$5 at 100 MeV, angular resolution of 1.5$^{22}$6 at 1 MeV and 0.15$^{22}$7 at 1 GeV, and 3$^{22}$8 line sensitivities in $^{22}$9 s of $r$0 ph cm$r$1 s$r$2 at 511 keV and $r$3 ph cm$r$4 s$r$5 at 847 keV (Angelis et al., 2016). These values are best read as mission heritage rather than as a frozen specification for the 2025 configuration.

Polarimetric performance is another defining element. The 2025 concept states that, around 300–500 keV, a Minimum Detectable Polarization of order 10–20% in $r$6 s on a 1 Crab source is achievable, using

$r$7

where $r$8 is the modulation factor and $r$9 and $p$0 are source and background count rates (Berge et al., 10 Jul 2025). Earlier e-ASTROGAM simulations reported $p$1–0.4 in the 150–500 keV band and projected detailed GRB, AGN, Crab, and Cygnus X-1 polarimetry (Tatischeff et al., 2017).

5. Principal scientific applications

The most developed application in the ASTROGAM literature is the diagnosis of relativistic outflows through MeV polarimetry and spectroscopy. For AGN and blazars, the MeV band constrains whether inverse-Compton emission is seeded by polarized synchrotron photons or by external unpolarized fields; for GRBs it distinguishes synchrotron, photospheric, and other prompt-emission mechanisms; for microquasars it separates corona-dominated Comptonization from jet synchrotron or synchrotron-self-Compton components (Tatischeff et al., 2017). In the e-ASTROGAM simulations, a polarization fraction $p$2 could be measured in $p$3 GRBs per year and $p$4 in $p$5 GRBs per year, while the Crab pulsar and nebula and Cygnus X-1 would be accessible to much faster, more precise polarimetry than achieved by INTEGRAL/IBIS (Tatischeff et al., 2017).

Nuclear-line astrophysics is the second major pillar. Published e-ASTROGAM line sensitivities include $p$6 ph cm$p$7 s$p$8 at 511 keV, $p$9 ph cm$\sim 500$0 s$\sim 500$1 at 847 keV for $\sim 500$2Co, $\sim 500$3 ph cm$\sim 500$4 s$\sim 500$5 at 1157 keV for $\sim 500$6Ti, and $\sim 500$7 ph cm$\sim 500$8 s$\sim 500$9 at 1275 keV for $\pi^0$0Na, all for $\pi^0$1 in $\pi^0$2 s and with improvements over INTEGRAL/SPI ranging from $\pi^0$3 to $\pi^0$4 depending on the line (Tatischeff et al., 2016). This performance underpins claims that the observatory family could detect $\pi^0$5 Type Ia supernovae up to $\pi^0$6 Mpc in 3 years, uncover young $\pi^0$7Ti-emitting remnants obscured at other wavelengths, and map $\pi^0$8Al and low-energy cosmic-ray-induced lines in the interstellar medium (Tatischeff et al., 2016, Tatischeff et al., 2017).

For Galactic high-energy ecology, the MeV–GeV interval is singled out as the regime where hadronic and leptonic channels separate most clearly. The literature repeatedly emphasizes the $\pi^0$9 turnover at MeV energies, the separation of bremsstrahlung and inverse-Compton emission from hadronic gamma rays in supernova remnants and superbubbles, the imaging of the Fermi Bubbles below 1 GeV, and the mapping of the 511 keV positron-annihilation morphology with degree-scale resolution (Tatischeff et al., 2016, Tatischeff et al., 2017, Angelis et al., 2021). A plausible implication is that the combination of improved angular resolution and line capability is as important as raw sensitivity for disentangling diffuse Galactic components.

The same band is also used for particle-physics searches. In the e-ASTROGAM dark-matter and ALP literature, relevant observables include line and continuum signatures from light dark matter, spectral irregularities induced by photon–ALP oscillations, birefringence and dichroism in polarized gamma-ray beams, and coincident supernova-associated gamma-ray bursts from ALP reconversion (Roncadelli et al., 2017). More generally, the ASTROGAM program has consistently included axion-like particles, Lorentz-invariance-violation tests via GRB polarimetry, dark photons, primordial black-hole evaporation, and light-DM searches in the sub-GeV range (Angelis et al., 2017, Berge et al., 10 Jul 2025).

6. Technology heritage, feasibility, and status

A defining feature of the ASTROGAM program is its reliance on detector technologies presented as mature or space-proven. Across the literature, the tracker architecture is tied to silicon-strip heritage from AGILE and Fermi/LAT, the calorimeter to CsI(Tl) and related crystal systems with silicon-drift-detector or SiPM readout, the anticoincidence system to plastic scintillator vetoes derived from AGILE and Fermi, and the coded-mask element in the 2025 concept to heritage from INTEGRAL and Swift (Tatischeff et al., 2016, Angelis et al., 2021, Berge et al., 10 Jul 2025). The 2025 feasibility summary assigns TRL 9 to AC panels and onboard real-time processing and telemetry, TRL 7–8 to the silicon microstrip tracker, TRL 6–8 to calorimeter crystals plus SiPM/readout, and TRL 8 to the coded mask (Berge et al., 10 Jul 2025).

Mission implementation studies from the e-ASTROGAM period also specify real-time event selection, onboard burst searches over 0.1 ms–10 s and 30 keV–200 MeV, GPS timing at 1 $\sim 1$00s accuracy, and multiple observing modes including survey scanning, inertial pointing, and rapid ToO repointing (Angelis et al., 2016). The emphasis on open-observatory operation and guest-observer time was present already in the earliest mission framing (Tatischeff et al., 2016).

newASTROGAM remains a proposal rather than an operational mission. The 2025 paper identifies it explicitly as a concept proposed to the ESA call for medium-class mission ideas (M8) (Berge et al., 10 Jul 2025). A recurrent source of confusion is the existence of several ASTROGAM variants with different lower energy thresholds, fields of view, or orbital assumptions. The published record shows an evolving design space: e-ASTROGAM was an M5 MeV–GeV observatory in low-inclination LEO, All-Sky-ASTROGAM was a wide-FoV L2 transient monitor, ASTRO-MEV restated the M-class science case, and newASTROGAM added coded-mask hard-X-ray imaging while retaining the core Compton-plus-pair architecture (Tatischeff et al., 2016, Tatischeff et al., 2019, Angelis et al., 2021, Berge et al., 10 Jul 2025). This suggests that the stable identity of newASTROGAM lies less in a single fixed payload than in a sustained observational strategy: high-sensitivity access to the MeV band, coupled to imaging, timing, and polarimetry, for multi-messenger gamma-ray astrophysics.