arXiv subjects

Naomi Tsuji

Publications and source records attributed to Naomi Tsuji.

At least 19 recordsLinked to original sources

arXiv2026

Three-dimensional recoil-electron reconstruction using combined optical imaging and waveform readout for electron-tracking Compton cameras

Accurate reconstruction of recoil-electron directions is critical for enhancing the point-spread function of electron-tracking Compton cameras (ETCCs) in gamma-ray imaging. Although full three-dimensional (3D) readout systems achieve high-precision reconstruction, they are impractical for large-area detectors because of the enormous data volume. This study proposes and demonstrates a practical alternative for inferring the 3D recoil-electron direction in Compton scattering. This method combines a high-resolution two-dimensional optical image, a one-dimensional waveform signal, and a deep-learning-based method through simulations. The proposed method achieved an angular resolution of approximately $44^\circ$ for the recoil-electron direction in the 40-50 keV range, corresponding to an improvement of a factor of about 1.3 compared with our previous strip-readout approach using pseudo-experimental data generated by Geant4 and MAGBOLTZ simulations for an argon-based gas time projection chamber. In addition, the starting-point resolution of the electron track was improved over the previous method across the 5-50 keV electron energy range. These results demonstrate that complementary information from the transverse image and longitudinal waveform can effectively recover the 3D track topology without requiring full 3D readout. The proposed approach provides a realistic pathway for improving ETCC imaging performance.

physics.ins-det↗

arXiv2026

Parameter estimation from the transit light curve including gravitational lensing effects

We study transit light curves of exoplanets, incorporating gravitational lensing effects, and explore the possibility of estimating planetary masses using only the transit light curve. We analyze existing data for planets with relatively large orbital distances ($>1$ AU) from Kepler and TESS to evaluate how well their masses can be constrained. For six exoplanets, we derive 2$σ$ upper limits of 200-2000 Jupiter masses. We also construct mock data to assess the feasibility of determining masses for exoplanets with larger orbital radii than currently known. Our results show that a precision of $3\times 10^{-6}$ is required to recover the true masses of planets with 10 (5) Jupiter masses at orbital radii of $a=20$ (100) AU. Furthermore, we demonstrate that neglecting gravitational effects can lead to underestimation of exoplanet radii, particularly for planets with large orbital separations. Using mock data with a precision of $2\times 10^{-4}$, assuming a 30 minutes cadence with Kepler for a $K_p=14$ mag star, we find that the estimated radii can be underestimated by 1-20% for 5 and 10 Jupiter-mass planets with $a=$ 10-100 AU. These results highlight the importance of including microlensing effects when modeling transit light curves of wide-orbit planets.

astro-ph.EP↗

arXiv2026

The Western Jet of SS 433/W50: Hard X-ray Emission, Spectral Evolution, and Comparison to the Eastern Jet

The W50 nebula powered by the microquasar SS 433 is a unique laboratory for exploring several fundamental astrophysical phenomena. This study presents observations from NuSTAR and XMM-Newton, concentrating on the western lobe of W50. Detection of hard non-thermal X-ray emission is reported, extending up to approximately 30 keV. This emission originates from a compact, knotty area referred to as the "Head", located at approximately 17 arcmin (equivalent to 26.5 pc at an assumed distance of 5.5 kpc) to the west of SS 433, and characterized by a power-law spectrum with a hard photon index of 1.55 +/- 0.07 (0.5-30 keV). Moving westward from SS 433, the photon index gradually steepens, ultimately reaching a photon index of 2.10 +/- 0.05 in the "w2" region centered at approximately 35 arcmin or approximately 56 pc from SS 433. The distinct hard X-ray knots observed serve as clear markers for sites of particle acceleration within the western jet. The synchrotron radiation from the "Head" region implies equipartition magnetic field strength B of approximately 15 microG. Notably, these properties (western "Head" location, unusually hard spectral index, inferred magnetic field, and spectral evolution away from SS 433) are very similar to what has been observed in the eastern lobe, supporting a symmetric jet-driven origin. Finally, the broadband spectral energy distribution (SED) and X-ray morphology are modeled using semi-analytic jet models, exploring different jet velocity and magnetic field configurations. The results favor a scenario in which in-situ particle acceleration and synchrotron emission dominate, with implications for understanding particle transport, jet dynamics, and W50's role as a Galactic PeVatron.

astro-ph.HE↗

arXiv2026

Multiwavelength Probes of Cosmic Ray Transport in Molecular Cloud Structures

We investigate how cosmic ray (CR) transport in molecular clouds and their substructures can be probed using multi-wavelength observations. The detailed microphysics regulating the penetration and coupling of CRs in dense molecular structures is unsettled. Self-generated turbulence can produce scattering and diffusive transport, while ion-neutral damping in cold, dense gas promotes ballistic CR propagation. We construct a self-consistent framework for CR transport and interactions in magnetized molecular clouds, considering three limiting propagation scenarios: ballistic transport, diffusion, and a hybrid configuration with a diffusive envelope and quasi-ballistic core. By forward-modeling pion-decay $γ$-ray emissivities, CR-driven ionization-rate profiles, and electron synchrotron emission in the hard X-ray band, we connect GeV attenuation and propagation signatures to independent diagnostics of secondary production and CR penetration. As an illustrative example, we apply our framework to the Taurus molecular cloud complex and selected embedded clumps. We show that CR scattering may be substantially enhanced on clump scales, with inferred CR diffusion coefficients suppressed relative to canonical interstellar medium (ISM) values at GeV energies. In this interpretation, CRs are more closely coupled with dense gas in the ISM, and a diffusive envelope boosts the effective gas column density encountered by the CRs. This increases the hadronic interaction rate in the cloud. In turn, the secondary CR electron injection is also increased, and CR ionization rates are elevated at higher densities. We show that a hard X-ray synchrotron emission component is also generated, which may be detectable with near-future facilities. Finally, we discuss how future $γ$-ray, X-ray, and ionization constraints will provide firm tests of CR propagation theories in molecular cloud environments.

astro-ph.HE↗

arXiv2025

The first proper motion measurement of the acceleration regions in the large-scale jets of SS 433 powering the W50 nebula

We report on new Chandra ACIS-I observations of the X-ray knots located in the western and eastern lobes of W50 associated with the parsec-scale jets of the Galactic microquasar SS 433. These knots are likely counterparts of the recently detected very-high-energy ($E>100$ GeV) gamma-ray emission by HAWC and H.E.S.S. These findings, together with the ultra-high-energy signal recently reported by the LHAASO collaboration, have established the SS 433/W50 system as a unique jet-driven PeVatron candidate. Combining new and archival Chandra data, we perform the first proper motion search of the X-ray knot structures over a time interval spanning approximately 20 years. We found no statistically significant motion of these knots at the 3$σ$ confidence level, and place an upper limit of $<$ 0.019-0.033$c$ (5,800-9,800 km s$^{-1}$) for the speed of the innermost knots at an assumed distance $d=5.5$ kpc. Combined with the velocities reported in the literature, the upstream speed in the shock rest frame would reach several 10$^4$ km s$^{-1}$, suggesting that highly efficient particle acceleration, approaching the Bohm limit, is occurring. The absence of significant motion of the knots suggests the presence of a standing recollimation shock, formed by the balance between the jet pressure and the external pressure. This interpretation is consistent with the expected occurrence of such shocks at 20-30 pc from SS 433, matching the location of the observed knots.

astro-ph.HE↗

arXiv2025

XRISM reveals a variable, multi-phase outflow-inflow structure during the X-ray obscured 2024 outburst of the black hole transient V4641 Sgr

We report the results of a simultaneous X-ray and optical spectroscopy campaign on the Galactic black hole X-ray binary V4641 Sgr, carried out with XRISM and the Seimei telescope during a low-luminosity phase towards the end of its 2024 outburst. Despite a very low X-ray luminosity of $10^{34}$ erg s$^{-1}$, the continuum spectrum is well reproduced by a disk blackbody model with a high inner disk temperature ($1.8$ keV). XRISM/Resolve provides the highest-resolution X-ray spectrum ever obtained from the source, and several strong, narrow emission lines were detected, resolved and characterized at a high significance level. The continuum shape and narrow emission lines both indicate that the inner disk region is obscured by the surrounding high-density gas, and the intrinsic luminosity is several orders of magnitude higher. In the simultaneous optical observation from the Seimei telescope, the line features are largely dominated by the optical companion. Although we detect a clear emission component in H$α$ that could originate from a cold outflow or the disk atmosphere, there are no signs of the strong outflow signatures historically detected in this source. In X-rays, the combination of significantly redshifted ($\sim 700$ km s$^{-1}$) and weakly blueshifted ($\sim-250$ km s$^{-1}$) components, all varying strongly on ks timescales, along with a marginally significant (99.2%) highly blueshifted ($\sim-1200$ km s$^{-1}$) component, indicates a complex, inhomogeneous outflow geometry. This is corroborated by the erratic long-term evolution of the source seen in the complementary X-ray monitoring, and radio detections spanning 3 orders of magnitude.

astro-ph.HE↗

arXiv2025

Systematic Biases from ARM-Based Sensitivity and Imaging in Compton Cameras

The angular resolution measure (ARM) is widely used in Compton camera analyses to characterize angular uncertainty and to define event selection criteria. However, the ARM distribution is fundamentally different from the point spread function (PSF), which represents the true spatial imaging response of the system on the celestial sphere. In this study, motivated by applications in gamma-ray astrophysics, we investigated the consequences of using ARM-based definitions in sensitivity estimation and image reconstruction. Through Monte Carlo simulations of 662 keV gamma-rays, we demonstrated that the background rejection power of ARM-based region-of-interest selections with the ARM resolution of 7.0$^{\circ}$ is equivalent to that of a PSF resolution of 33$^{\circ}$. As a result, treating the ARM resolution as a surrogate for the PSF resolution leads to significant overestimation of the signal-to-noise ratio, particularly in analyses assuming isotropic backgrounds. We further show that image reconstructions at pixel scales finer than the PSF resolution introduce substantial statistical uncertainties, reducing the effective number of independent spatial degrees of freedom. These findings underscore the necessity of PSF-based analysis for accurate sensitivity evaluation and statistically robust imaging in Compton cameras, particularly in applications where the background discrimination is critical.

astro-ph.IM↗

arXiv2025

X-ray Study on Propagation of Non-thermal Particles in Microquasar SS 433/W 50 Extended Jets

SS 433, located at the center of the W 50 radio nebula, is a binary system that ejects jets oriented east-west with precessional motion. X-ray lobes, containing compact "knots" labeled as head (e1), lenticular (e2), and ring (e3) in the east, as well as w1, w1.5, and w2 in the west, have been detected along the jets directions. Very-high-energy γ-ray emission has also been detected from regions containing these X-ray knots, suggesting highly efficient particle acceleration in the jets. In our previous study, we performed X-ray imaging spectroscopy of the western lobe of W 50 to investigate spectral variations. In this work, we extend our study to the eastern region using XMM-Newton observations to provide a more comprehensive picture of the X-ray emission from the SS 433 jets. Our results show no detectable synchrotron emission between SS 433 and the innermost knot (head). We also found that the X-ray spectrum of the eastern jet gradually steepens as one moves away from SS 433. While a similar spectral evolution is observed in the western jet, there are also noticeable differences. In the western lobe, the spectrum initially gradually steepens and then undergoes an abrupt softening outside the knot w2. However, in the eastern jet, no such rapid steepening is observed at the lenticular knot, which corresponds to w2 in the west. Furthermore, the observed brightening and spectral variations in the eastern jet cannot be explained by simply adjusting the parameters of the model used for the western side, suggesting the involvement of additional physical processes such as particle re-acceleration.

astro-ph.HE↗

arXiv2025

The Moon as a Cosmic-Ray Spectrometer: Prospects for MeV Gamma-Ray Observations

The Moon is the closest celestial gamma-ray emitting object. Its gamma-ray emission arises from interactions between Galactic cosmic rays (CRs) and the lunar surface. While the lunar GeV gamma-ray spectrum is dominated by a continuum from hadronic decay processes, the MeV emission exhibits both continuum and distinctive spectral lines from nuclear de-excitation and radioactive decay processes. Using Geant4 Monte Carlo particle simulations, we model the lunar gamma-ray spectrum. Our results demonstrate its consistency with Fermi-LAT observations, and predict that next-generation MeV gamma-ray instruments will detect both the lunar MeV continuum and several key spectral line features, notably the $1.779~\mathrm{MeV}$ line from $\mathrm{^{28}Si}$ de-excitation enhanced by the lunar surface composition, the $e^+e^-$ annihilation line, and radioactive decay lines from $\mathrm{^{22}Na}$ ($τ\approx3.75\,\mathrm{yr}$) and long-lived $\mathrm{^{26}Al}$ ($τ\approx1\,\mathrm{Myr}$). These gamma-ray lines are sensitive to CRs with energies $\lesssim1\,\mathrm{GeV\,nuc^{-1}}$, offering unique temporal probes of CR activity over different timescales. Observations of the lunar MeV gamma-ray spectrum will therefore open a new window to study the current irradiation of the solar-terrestrial environment by low-energy CRs and its long-term temporal evolution.

astro-ph.HE↗

arXiv2025

Detection of molecular clouds in the PeVatron candidate source LHAASO J0341$+$5258 by the Nobeyama 45-m radio telescope

We report a new CO observation survey of LHAASO J0341$+$5258 using the Nobeyama Radio Observatory (NRO) 45-m telescope. LHAASO J0341$+$5258 is one of the unidentified ultra-high-energy (UHE; E $>$100 TeV) gamma-ray sources detected by LHAASO. Our CO observations were conducted in February and March 2024, with a total observation time of 36 hours, covering the LHAASO source ($\sim$0.3-0.5 degrees in radius) and its surrounding area (1$\times$1.5 degrees). Within the LHAASO source extent, we identified five compact ($<$ 2 pc) molecular clouds at nearby distances ($<$ 1-4 kpc). These clouds can serve as proton-proton collision targets, producing hadronic gamma rays via neutral pion decays. Based on the hydrogen densities (700-5000 cm$^{-3}$) estimated from our CO observations and archived HI data from the DRAO survey, we derived the total proton energy of $W_p$ (E $>$ 1 TeV) $\sim$ 10$^{45}$ erg to account for the gamma-ray flux. One of the molecular clouds appears to be likely associated with an asymptotic giant branch (AGB) star with an extended CO tail, which may indicate some particle acceleration activities. However, the estimated maximum particle energy below 100 TeV makes the AGB-like star unlikely to be a PeVatron site. We conclude that the UHE emission observed in LHAASO J0341$+$5258 could be due to hadronic interactions between the newly discovered molecular clouds and TeV-PeV protons originating from a distant SNR or due to leptonic emission from a pulsar wind nebula candidate, which is reported in our companion X-ray observation paper (DiKerby et al. 2025).

astro-ph.HE↗

arXiv2025

Discovery of a Pulsar Wind Nebula Candidate Associated with the Galactic PeVatron 1LHAASO J0343+5254u

The astronomical origin of the most energetic galactic cosmic rays and gamma rays is still uncertain. X-ray followup of candidate "PeVatrons", systems producing cosmic rays with energies exceeding 1 PeV, can constrain their spatial origin, identify likely counterparts, and test particle emission models. Using 120 ks of XMM-Newton observations, we report the discovery of a candidate pulsar wind nebula, a possible counterpart for the LHAASO PeVatron J0343+5254u. This extended source has a power law X-ray spectrum with spectral index of 1.9 - softer at greater distance from the center - and asymmetric spatial extension out to 2'. We conduct leptonic modeling of the X-ray and gamma ray radiation from this complex system, showing that a fully leptonic model with elevated IR photon fields can explain the multiwavelength emission from this source, similar to other VHE pulsar wind nebulae; excess gamma ray emissivity not explained by a leptonic model may be due to hadronic interactions in nearby molecular cloud regions, which might also produce detectable astroparticle flux.

astro-ph.HE↗

arXiv2024

Detection of extended X-ray emission around the PeVatron microquasar V4641 Sgr with XRISM

A recent report on the detection of very-high-energy gamma rays from V4641 Sagittarii (V4641 Sgr) up to ~0.8 peta-electronvolt has made it the second confirmed "PeVatron" microquasar. Here we report on the observation of V4641 Sgr with X-Ray Imaging and Spectroscopy Mission (XRISM) in September 2024. Thanks to the large field of view and low background, the CCD imager Xtend successfully detected for the first time X-ray extended emission around V4641 Sgr with a significance of > 4.5 sigma and > 10 sigma based on our imaging and spectral analysis, respectively. The spatial extent is estimated to have a radius of $7 \pm 3$ arcmin ($13 \pm 5$ pc at a distance of 6.2 kpc) assuming a Gaussian-like radial distribution, which suggests that the particle acceleration site is within ~10 pc of the microquasar. If the X-ray morphology traces the diffusion of accelerated electrons, this spatial extent can be explained by either an enhanced magnetic field (~80 uG) or a suppressed diffusion coefficient (~$10^{27}$ cm$^2$ s$^{-1}$ at 100 TeV). The integrated X-ray flux, (4-6)$\times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$ (2-10 keV), would require a magnetic field strength higher than the galactic mean (> 8 uG) if the diffuse X-ray emission originates from synchrotron radiation and the gamma-ray emission is predominantly hadronic. If the X-rays are of thermal origin, the measured extension, temperature, and plasma density can be explained by a jet with a luminosity of ~$2\times 10^{39}$ erg s$^{-1}$, which is comparable to the Eddington luminosity of this system.

astro-ph.HE↗

arXiv2024

Spectrum and location of ongoing extreme particle acceleration in Cassiopeia A

Young supernova remnants (SNRs) are believed to be the origin of energetic cosmic rays (CRs) below the "knee" of their spectrum at $\sim3$ petaelectronvolt (PeV, $10^{15}$ eV). Nevertheless, the precise location, duration, and operation of CR acceleration in young SNRs are open questions. Here, we report on multi-epoch X-ray observations of Cassiopeia A (Cas A), a 350-year-old SNR, in the 15-50 keV band that probes the most energetic CR electrons. The observed X-ray flux decrease $(15\pm1\%)$, contrary to the expected $>$90\% decrease based on previous radio, X-ray, and gamma-ray observations, provides unambiguous evidence for CR electron acceleration operating in Cas A. A temporal model for the radio and X-ray data accounting for electron cooling and continuous injection finds that the freshly injected electron spectrum is significantly harder (exponential cutoff power law index $q=2.15$), and its cutoff energy is much higher ($E_{cut}=36$ TeV) than the relic electron spectrum ($q=2.44\pm0.03$, $E_{cut}=4\pm1$ TeV). Both electron spectra are naturally explained by the recently developed modified nonlinear diffusive shock acceleration (mNLDSA) mechanism. The CR protons producing the observed gamma rays are likely accelerated at the same location by the same mechanism as those for the injected electron. The Cas A observations and spectral modeling represent the first time radio, X-ray, gamma ray and CR spectra have been self-consistently tied to a specific acceleration mechanism -- mNLDSA -- in a young SNR.

astro-ph.HE↗

arXiv2024

MeV gamma rays from Q-ball decay

We study the supersymmetric Q balls which decay at present and find that they create a distinctive spectrum of gamma rays at around O(10) MeV. The charge of the Q ball is lepton numbers in order for the lifetime to be as long as the present age of the universe, and the main decay products are light leptons. However, as the charge of the Q ball decreases, the decay channel into pions becomes kinematically allowed towards the end of the decay, and the pions are produced at rest. Immediately, $π^0$ decays into two photons with the energy of 67.5 MeV, half the pion mass, which exhibits a unique emission line. In addition, $π^\pm$ decay into $μ^\pm$, which further decay with emitting internal bremsstrahlung, whose spectrum has a sharp cutoff at $\sim$50 MeV. If the observations would find these peculiar features of the gamma-ray spectrum in the future, it could be a smoking gun of the supersymmetric Q-ball decay at present.

hep-ph↗

arXiv2024

Search for synchrotron emission from secondary electrons of proton-proton interaction in Galactic PeVatron candidate HESS J1641$-$463

HESS J1641-463 is an unidentified gamma-ray source with a hard TeV gamma-ray spectrum, and thus it has been proposed to be a possible candidate for cosmic ray (CR) accelerators up to PeV energies (a PeVatron candidate). The source spatially coincides with the radio supernova remnant (SNR) G338.5+0.1, but has not yet been fully explored in the X-ray band. We analyzed newly taken NuSTAR data, pointing at HESS J1641-463, with 82 ks effective exposure time. There is no apparent X-ray counterpart of HESS J1641-463, while nearby stellar cluster, Mercer 81, and stray-light X-rays are detected. Combined with the archival Chandra data, partially covering the source, we derived an upper limit of $\sim 6\times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ in 2-10 keV ($\sim 3\times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ in 10-20 keV). If the gamma-ray emission is originated from decay of $π^0$ mesons produced in interactions between CR protons and ambient materials, secondary electrons in the proton-proton interactions can potentially emit synchrotron photons in the X-ray band, which can be tested by our X-ray observations. Although the obtained X-ray upper limits cannot place a constraint on the primary proton spectrum, it will be possible with a future hard X-ray mission.

astro-ph.HE↗

arXiv2023

The High Energy X-ray Probe (HEX-P): Galactic PeVatrons, star clusters, superbubbles, microquasar jets, and gamma-ray binaries

HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10" FWHM) and broad spectral coverage (0.2-80 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. With the recent discoveries of over 40 ultra-high-energy gamma-ray sources (detected above 100 TeV) and neutrino emission in the Galactic Plane, we have entered a new era of multi-messenger astrophysics facing the exciting reality of Galactic PeVatrons. In the next decade, as more Galactic PeVatrons and TeV gamma-ray sources are expected to be discovered, the identification of their acceleration and emission mechanisms will be the most pressing issue in both particle and high-energy astrophysics. In this paper, along with its companion papers (Reynolds et al. 2023, Mori et al. 2023), we will present that HEX-P is uniquely suited to address important problems in various cosmic-ray accelerators, including Galactic PeVatrons, through investigating synchrotron X-ray emission of TeV-PeV electrons produced by both leptonic and hadronic processes.

astro-ph.HE↗

arXiv2023

The High Energy X-ray Probe (HEX-P): Supernova remnants, pulsar wind nebulae, and nuclear astrophysics

HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging ($<10"$ full width at half maximum) and broad spectral coverage (0.2--80 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. HEX-P is ideally suited to address important problems in the physics and astrophysics of supernova remnants (SNRs) and pulsar-wind nebulae (PWNe). For shell SNRs, HEX-P can greatly improve our understanding via more accurate spectral characterization and localization of non-thermal X-ray emission from both non-thermal-dominated SNRs and those containing both thermal and non-thermal components, and can discover previously unknown non-thermal components in SNRs. Multi-epoch HEX-P observations of several young SNRs (e.g., Cas A and Tycho) are expected to detect year-scale variabilities of X-ray filaments and knots, thus enabling us to determine fundamental parameters related to diffusive shock acceleration, such as local magnetic field strengths and maximum electron energies. For PWNe, HEX-P will provide spatially-resolved, broadband X-ray spectral data separately from their pulsar emission, allowing us to study how particle acceleration, cooling, and propagation operate in different evolution stages of PWNe. HEX-P is also poised to make unique and significant contributions to nuclear astrophysics of Galactic radioactive sources by improving detections of, or limits on, $^{44}$Ti in the youngest SNRs and by potentially discovering rare nuclear lines as evidence of double neutron star mergers. Throughout the paper, we present simulations of each class of objects, demonstrating the power of both the imaging and spectral capabilities of HEX-P to advance our knowledge of SNRs, PWNe, and nuclear astrophysics.

astro-ph.HE↗

arXiv2023

The origin of MeV gamma-ray diffuse emission from the inner Galactic region

The origin of the inner Galactic emission, measured by COMPTEL with a flux of $\sim ~ 10^{-2}$ MeV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ in the 1-30 MeV range, has remained unsettled since its discovery in 1994. We investigate the origin of this emission by taking into account individual sources which are not resolved by COMPTEL and the Galactic diffuse emission. The source contribution is estimated for sources crossmatched between the Swift-BAT and Fermi-LAT catalogs by interpolating the energy spectra in the hard X-ray and GeV gamma-ray ranges, as well as unmatched sources. This results in a flux of $\sim$20% of the COMPTEL excess. The Galactic diffuse emission is calculated by GALPROP to reconcile the cosmic-ray and gamma-ray spectra with observations by AMS-02, Voyager, and Fermi-LAT, resulting in a flux of $\sim$30-80% of the COMPTEL emission. Thus, we show that the COMPTEL emission could be roughly reproduced by a combination of the sources and the Galactic diffuse emission. Furthermore, combined with the extragalactic emission, we construct all-sky images in the MeV gamma-ray range to pinpoint some potential interesting targets for future missions, which would be critical for bridging the MeV gap in the spectra of gamma-ray sources.

astro-ph.HE↗