MeV Gamma Rays Research Articles

Spatial distribution of gamma rays produced by axially symmetric polarized and optical vortex lasers

The polarization properties and spatial distribution of electromagnetic radiation emitted from a high-energy electron can be calculated using the Lienard-Wiechert potentials. These properties are characterized by changes in electron orbitals. In Thomson or Compton scattering by relativistic electrons, which involves the interaction between electrons and a laser, the transverse motion of the electrons is induced by the laser's electric field. The polarization characteristics and spatial distribution of emitted radiation in linearly and circularly polarized laser fields have been extensively studied. In this paper, using a CdTe image sensor, the spatial distribution of MeV gamma rays generated by a 90-degree collision between a 750 MeV electron beam and an axially symmetric polarized laser was measured. The axially symmetric polarized laser, which includes radially and azimuthally polarized components, was created from a linearly polarized laser using a spatially variant retarder known as an s-waveplate. The spatial distribution of gamma rays exhibited a peak at the center, similar to linearly and circularly polarized gamma rays, but differed in overall contour from both. This result suggested that axially symmetric polarized lasers generated gamma rays with different polarization states. Moreover, the contour was observed to change with the polarization axis of the axially symmetric polarized laser, likely owing to the nonuniform distribution of the laser's polarization intensity. Additionally, the spatial distribution of gamma rays produced by circularly polarized optical vortex lasers was measured, showing that their contours corresponded to those of nonvortex circularly polarized lasers. Published by the American Physical Society 2024

Precise measurement of pion-bump structure using future MeV gamma-ray detectors

Precise measurement of pion-bump structure using future MeV gamma-ray detectors

Search for MeV gamma-ray emission from TeV bright red dwarfs with COMPTEL

The SHALON atmospheric Cherenkov telescope has detected very high energy gamma-ray emission at TeV energies from eight red dwarfs, namely, V388 Cas, V547 Cas, V780 Tau, V962 Tau, V1589 Cyg, GJ 1078, GJ 3684 and GL 851.1. Consequently, these red dwarfs have been suggested as sources of ultra-high energy cosmic rays. In this work, we search for soft gamma-ray emission from these TeV bright red dwarfs between 0.75–30 MeV using archival data from the COMPTEL gamma-ray imaging telescope, as a follow-up to a similar search for GeV gamma-ray emission using the Fermi-LAT telescope. Although, prima-facie, we detect non-zero photon flux from three red dwarfs with high significance, these signals can attributed to contamination from nearby sources such as Crab and Cygnus, which are within the angular resolution of COMPTEL, and have been previously detected as very bright point sources at MeV energies. Therefore, we could not detect any statistically significant signal (> 3σ) from any of these eight red dwarfs from 0.75–30 MeV. We then report the 95% confidence level upper limits on the differential photon flux (at 30 MeV), integral photon flux and integral energy flux for all of the eight red dwarfs. The integral energy flux limits range between 10-11 - 10-10-ergs/cm2/s.

Conceptual design of a gamma-to-electron energy-selective imaging system for high-flux MeV gamma rays

A novel design for energy-selective imaging of high-flux gamma rays in the multi-MeV range is presented. The proposed system is based on gamma-to-electron conversion and energy-selective imaging of the electrons. The main components of the system include a low-Z foil that converts MeV gamma-ray photons into electrons through Compton scattering, and a double-bend beam transport system that performs energy selection and point-to-point imaging for the electrons. The image of the energy-selected electrons can be used to obtain spatial information for incident gamma rays of interest energy, enabling energy-selective imaging of broad-spectrum gamma-ray beams. Design considerations and optimizations are detailed. Monte Carlo simulations are conducted to evaluate the performance in energy-selective imaging of broad-spectrum gamma-ray beams. The energy resolution for 4.44 MeV gamma-ray achieves 0.41 MeV (FWHM) with a quantum efficiency of 2.5 × 10−6 e/γ, and the spatial resolution is approximately 1 mm and 2.5 mm within a 60 × 60 mm field of view in the horizontal (x) and vertical (y) directions, respectively.

Reviving MeV-GeV indirect detection with inelastic dark matter

Thermal relic dark matter below ∼10 GeV is excluded by cosmic microwave background data if its annihilation to visible particles is unsuppressed near the epoch of recombination. Usual model-building measures to avoid this bound involve kinematically suppressing the annihilation rate in the low-velocity limit, thereby yielding dim prospects for indirect detection signatures at late times. In this work, we investigate a class of cosmologically viable sub-GeV thermal relics with late-time annihilation rates that are detectable with existing and proposed telescopes across a wide range of parameter space. We study a representative model of inelastic dark matter featuring a stable state χ1 and a slightly heavier excited state χ2 whose abundance is thermally depleted before recombination. Since the kinetic energy of dark matter in the Milky Way is much larger than it is during recombination, χ1χ1→χ2χ2 upscattering can efficiently regenerate a cosmologically long-lived Galactic population of χ2, whose subsequent coannihilations with χ1 give rise to observable gamma-rays in the ∼1 MeV−100 MeV energy range. We find that proposed MeV gamma-ray telescopes, such as e-ASTROGAM, AMEGO, and MAST, would be sensitive to much of the thermal relic parameter space in this class of models and thereby enable both discovery and model discrimination in the event of a signal at accelerator or direct detection experiments. Published by the American Physical Society 2024

A Novel Cancer Therapy Using Proton Beam: An Integrated Proton-Dynamic Therapy, iPDT

[Background and Aims]A super-aged society, the prime example of which is Japan, is being flooded with increasing in numerous numbers of aged cancer patients, who often take anti-coagulant medicines to prevent the attacks of ischemic heart diseases and/ or strokes. Since they show bleeding tendency induced by the medicines, it’s hard for them to receive surgical operations. Thus, low invasive cancer treatments without bleedings are abundantly desired. In this study, the applicant will establish a new proton therapy, in which a resonance nuclear reaction (RNR) induced by collision of a proton with a stable nitrogen isotope (15N), can be a clue to injure cancer-cells specifically. The LET of the product ions (12C6+, 4He2+) of the 15N RNR is above 50 times in comparison with the LET of proton. To establish the cancer-specific 15N delivery, 15N-aminolevulinic acid (15N-ALA) will be used. This reagent has been already used and obtained regulatory approvals as a diagnostic medicine for the location of the glioblastoma in Japan.[Methods]In this study, a pair of rat gastric epithelial cells, one is normal cell RGM1, and another is cancerous characteristics cells RGK1 were used. The authors treated these cells with both 1mM 15N-ALA and 14N-ALA. Thereafter, we measured and compared porphyrin fluorescent intensity of these cells. Moreover, these cells will be irradiated with 4 nc proton beam generated by an electrostatic accelerator, then 4.43 MeV gamma-rays will be measured to demonstrate the amount of 15N collected specifically in the tumour cells. After these proton irradiations, cells were stained with hoechest33258 and dapi to observe cellular apoptosis.[Results] Cancer cells accumulated 9 folds of 15N in comparison with normal epithelial cells. After 3hours of proton irradiation, both cancer cells and normal cells were not injured. However, almost all cancer cells were died with apoptosis while normal cells showed few cellular injuries after 24 hours.[Conclusions] Cancer cells were completely killed by RNR involved with imM 15N-ALA and 4nc proton irradiation whereas this dose of proton showed few effects of ionizing radiation on normal cells. Thus, iPDT should be an ideal treatment for cancer. Moreover, the quantitative analysis of 15N in the tumour cells can be a new pre-diagnosis for iPDT.

Radioactive Gamma-Ray Lines from Long-lived Neutron Star Merger Remnants

The observation of a kilonova AT2017gfo associated with the gravitational wave event GW170817 provides the first strong evidence that neutron star mergers are dominant contributors to the production of heavy r-process elements. Radioactive gamma-ray lines emitted from neutron star merger remnants provide a unique probe for investigating the nuclide composition and tracking its evolution. In this work, we studied the gamma-ray line features arising from the radioactive decay of heavy nuclei in the merger remnants based on the r-process nuclear reaction network and the astrophysical inputs derived from numerical relativity simulations. The decay chain of 50126 Sn (T 1/2 = 230 kyr) → 51126 Sb (T 1/2 = 12.35 days) → 52126 Te (stable) produces several bright gamma-ray lines with energies of 415, 667, and 695 keV, making it the most promising decay chain during the remnant phase. The photon fluxes of these bright gamma-ray lines reach ∼10−5 γ cm−2 s−1 for Galactic merger remnants with ages less than 100 kyr, which can be detected by the high energy resolution MeV gamma-ray detectors like the MASS mission.

Structural, thermo-mechanical, optical and gamma-ray shielding properties of lead-free BaO–ZnO–B2O3–SiO2 and lead-based PbO–Bi2O3–K2O–SiO2 glasses

Lead-free BaO–ZnO–B2O3–SiO2 glass (BZBS) and lead-based PbO–Bi2O3–K2O–SiO2 glass (LS) were synthesized by melt quench technique. Glass samples were irradiated using 60Co gamma source up to 50 kGy dose to study the changes in structural, thermo-mechanical, optical and gamma ray shielding properties. Measured density values of both the glasses were greater than 4.0 g/cc. X Ray Diffraction (XRD) studies confirmed amorphous nature of prepared glasses before and after gamma irradiation. The structural changes induced by gamma irradiation were also investigated using Raman, Positron annihilation lifetime spectroscopy (PALS) and Electron Paramagnetic Resonance (EPR) spectroscopy. PALS data revealed increase in free volume/voids after irradiation. Defect studies carried using EPR spectroscopy confirmed formation of electron trap centre in BZBS glass, whereas in LS glass in addition to the electron trap centers, non-bridging oxygen hole centers (NBOHC) and peroxy radical defects were also observed. Investigations on thermo-mechanical properties demonstrated higher glass transition temperature (Tg), hardness and modulus of elasticity values for BZBS glass as compared to the LS glass, which were found to be decreased after irradiation because of radiation induced defects. Visible transparency and band gap for BZBS glass were found to be higher than that in LS glass. After irradiation, colour change, reduction in transparency as well as band gap, and red shift in absorption edge were observed due to the formation of defects in both the glasses. The values of radiation induced absorption (α) at three different visible wavelengths have been determined for 50 kGy dose using UV–Vis transmission data. Analysis of refractive index data showed around 12 % reflection losses for both the glasses. Annealing of irradiated samples using UV light source showed significant improvement in transparency. Linear attenuation coefficient (LAC) was calculated using XCOM program and experimentally measured using 60Co 1.33 MeV gamma ray. Linear attenuation coefficient of BZBS glass was around 0.20 cm−1 whereas for LS glass value was 0.24 cm−1. Half value layer thickness of prepared glasses was also compared with available standard materials and it was found that prepared glasses may be suitable for shielding of high energy gamma rays.

Multiwavelength Emission of the Gamma-Ray Burst Prompt Phase. I. Time-resolved and Time-integrated Polarizations

The time-integrated polarization degree (PD) in the prompt optical band of a gamma-ray burst (GRB) was predicted to be less than 20%, while the time-resolved one can reach as high as 75% in the photosphere model. Polarizations in the optical band during the GRB prompt phase have not previously been studied in the framework of the magnetic reconnection model. Here, a three-segment power law of the energy spectrum is used to reconstruct the Stokes parameters of the magnetic reconnection model. Multiwavelength light curves and polarization curves from the optical band to MeV gamma rays in the GRB prompt phase are studied. We found that, depending mainly on the jet dynamics, there is a long-lasting high-PD phase in all calculated energy bands for the typical parameter sets. The time-resolved PD could be as high as 50%, while the time-integrated one is roughly 17% in the optical band. The time-resolved PD in X-rays can reach 60% and the time-integrated one is around 30%–40%. The evolution of polarization angle (PA) is random in both optical and gamma-ray bands for the photosphere model, while it is roughly constant in the synchrotron models. Therefore, future time-resolved PA observations in the prompt optical or gamma-ray band could distinguish between the photosphere and synchrotron models.

Investigation of nano MgO loaded polyvinyl chloride polymer in protective clothing as a nonlead materials

Recently, investigation of advanced shielding materials to be used as an alternative to lead apron has become important. In the current study, MgO loaded into PVC matrix as a non-lead modern shielding composite was modeled to evaluate its performance on radiation protective clothing (RPC). Parameters such as mass attenuation coefficient (MAC), mean free path (MFP), flux buildup factor (FBF), transmission factor (TF) and lead equivalent value (LEV) of samples were calculated using MCNPX Code. The simulation of the MCNP code was validated, by comparing the mass attenuation of concrete sample, with standard XCOM data and very good agreement was attended between XCOM and MC Code results. The MAC of nano and micro-sized samples were also compared with pure PVC and it was found that the nano MgO particle exhibits higher attenuation compared to micro MgO particle and pure PVC. The results show that, the MAC of samples increased to 63.13 % in 1.332 MeV with increasing filler concentration of nano MgO to 50 wt% relative to pure PVC. Investigation of LEV shows that nano MgO sample has more effective than Pb in 1.173 and 1.332 MeV gamma ray energy so that it provides 36.46 % and 11.13 % lighter RPC than Pb ones.

New lead barium borate glass system for radiation shielding applications: impacts of copper (II) oxide on physical, mechanical, and gamma-ray attenuation properties

Abstract The current work seeks to develop a novel CuO-doped lead calcium barium borate glass using the melt quenching method at 1100 °C. There was a 3.91–4.49 g/cm3 change in the fabricated glasses’ density, with a respective 0–15 mol.% increase in the CuO concentration. Additionally, substituting CuO for B2O3 reduced the fabricated glasses mechanical properties due to the decreased dissociation energy between 63.99 and 60.50 kcal/cm3, and the packing factor decreased between 15.22 and 13.23 cm3/mol. Through increasing the fabricated glasses’ CuO concentration, there was a decrease in the bulk, longitudinal, shear, and mechanical Young moduli. Moreover, Monte Carlo simulation (energy interval: 0.033–2.506 MeV) was employed to evaluate the fabricated glasses’ ability to shield gamma rays. A 0–15 mol.% increase in the CuO concentration raised the linear attenuation coefficient (LAC) between 14.081 and 16.797 cm−1 (0.059 MeV), 0.325–0.371 cm−1 (0.662 MeV), and 0.154–0.176 cm−1 (2.506 MeV). The LAC enhancement reduced the required half value thickness of the fabricated glasses by 16.2 %, 12.53 %, and 12.85 % at the of 0.059, 0.662, and 2.506 MeV gamma ray energies.

A pilot search for MeV gamma-ray emission from five galaxy clusters using archival COMPTEL data

We search for MeV gamma-ray emission between 0.75–30 MeV from five galaxy clusters, viz. Coma, VIRGO, SPT-CL J2012-5649, Bullet, and El Gordo, using archival data from the COMPTEL telescope. For this purpose we use three search templates: point source, radial disk and radial Gaussian. We do not detect any signals from Coma, SPT-CL J2012-5649, Bullet and El Gordo clusters with the 95% c.l. photon energy flux limit ∼ 10-10erg/cm2/s.For VIRGO, we detect a non-zero signal between 0.75 to 1.50 MeV having marginal significance of about 2.5σ, with the observed energy flux equal to ∼ 10-9 ergs/cm2/s. However, we do not confirm the previously reported evidence in literature for a gamma-ray line from Coma and VIRGO clusters between 5–7 MeV.

A comparative analysis of shielding effectiveness in glass and concrete containers

Abstract Nuclear waste control and related equipment play a vital role in safeguarding human health and the environment from the potential dangers of radioactive waste. This study addresses the critical challenge of enhancing the shielding effectiveness of container materials for nuclear waste management, with a focus on comparing the attenuation properties of glass and concrete composites. Our analysis revealed that the copper oxide-reinforced borosilicate glass container demonstrated a significant transmission factor (TF) value decrease by approximately 15% compared to steel–magnetite concrete at 1.3325 MeV, with a standard deviation of ±1.5%, indicating its lower protective characteristics. Nonetheless, it exhibited a 10% higher TF reduction compared to the cement–bitumen mix at the same energy level, with a precision error of ±1.2%. In addition, the half-value layer for this glass was determined to be 2.5 cm for 1.3325 MeV gamma rays, showing moderate shielding capacity. The study demonstrates that optimizing the oxide content in the borosilicate glass matrix significantly enhances its shielding effectiveness. This advancement in nuclear waste management materials is justified by our comprehensive evaluation, highlighting the potential of optimized glass materials to outperform traditional concrete in certain scenarios, thus contributing to the development of more effective nuclear waste containment solutions.

Structural, physical, optical, and gamma ray shielding properties of SnO2-based boro-silicate glasses: The influence of substituting Na2O by SnO2

The study focuses on creating new boro-silicate glasses doped with SnO2 for radiation shielding. It examines how substituting Na2O with SnO2 affects their structural, optical, and shielding properties. Density increases from 2.406 to 2.488 g/cm³ with rising SnO2, measured via the Archimedes Method. The examination for the glassy phase was performed using the XRD diffractometer. UV/Vis spectrophotometer analysis reveals reduced refractive index (2.412–1.976) and increased optical absorption-band gap (direct: 3.648–5.662 eV; indirect: 2.994–5.163 eV) with SnO2 concentrations of 0–9 mol.%). The effectiveness of the radiation shielding was assessed over the 0.059–1.408 MeV gamma-ray energy interval. The analysis demonstrates that when the concentration of SnO2 increases, the synthesized glasses' linear attenuation coefficient improves. As the SnO2 content was raised between 0 and 9 mol%, the linear attenuation coefficient rose between 0.489 and 2.892 cm−1 (at energy of 0.059 MeV) and between 0.126 and 0.128 cm−1 (at energy of 1.408 MeV), respectively. As the SnO2 content was raised between 0 and 9 mol%.

Study on the shielding performance of bismuth oxide as a spent fuel dry storage container based on Monte Carlo simulation

For traditional spent fuel shielding materials, due to physical and chemical defects and cost constraints, they have been unable to meet the needs. Therefore, this paper carries out the first discussion on the application and performance of bismuth in neutron shielding by establishing Monte Carlo simulation on the neutron flux model of shielded spent fuel. Firstly, functional fillers such as bismuth oxide, lead oxide, boron oxide, gadolinium oxide and tungsten oxide are added to the matrices to compare the shielding rates of aluminum alloy matrix and silicone rubber matrix. The shielding rate of silicone rubber mixture is higher than aluminum alloy mixture, reaching more than 56%. The optimal addition proportion of bismuth oxide and lead oxide is 30%, and the neutron radiation protection efficiency reaches 60%. Then, the mass attenuation coefficients of bismuth oxide, lead oxide, boron oxide, gadolinium oxide and tungsten oxide in silicone rubber matrix are simulated with the change of functional fillers proportion and neutron energy. This simulation result shows that the mixture with functional fillers has good shielding performance for low energy neutrons, but poor shielding effect for high energy neutrons. Finally, in order to further evaluate the possibility of replacing lead oxide with bismuth oxide as shielding material, the half-value layers and various properties of bismuth oxide and lead oxide are compared. The results show that the shielding properties of bismuth oxide and lead oxide are basically the same, and the mechanical properties, heat resistance, radiation resistance and environmental protection of bismuth oxide are better than that of lead oxide. Therefore, in the case of neutron source strengths in the range of 0.01–6 MeV and secondary gamma rays produced below 2.5 MeV, bismuth can replace lead in neutron shielding applications.

High-energy extension of the gamma-ray band observable with an electron-tracking Compton camera

Although the MeV gamma-ray band is a promising energy-band window in astrophysics, the current situation of MeV gamma-ray astronomy significantly lags behind those of the other energy bands in angular resolution and sensitivity. An electron-tracking Compton camera (ETCC), a next-generation MeV detector, is expected to revolutionize the situation. An ETCC tracks each Compton-recoil electron with a gaseous electron tracker and determines the incoming direction of each gamma-ray photon; thus, it has a strong background rejection power and yields a better angular resolution than classical Compton cameras. Here, we study ETCC events in which the Compton-recoil electrons do not deposit all energies to the electron tracker but escape and hit the surrounding pixel scintillator array (PSA). The PSA provides additional information on the electron-recoil direction, which enables us to improve significantly the angular resolution. We developed an analysis method for this untapped class of events and applied it to laboratory and simulation data. We found that the energy spectrum obtained from the simulation agreed with that of the actual data within a factor of 1.2. We then evaluated the detector performance using the simulation data. The angular resolution for the new-class events was found to be twice as good as in the previous study at the energy range 1.0–2.0 MeV, where both analyses overlap. We also found that the total effective area is dominated by the contribution of the double-hit events above an energy of 1.5 MeV. Notably, applying this new method extends the sensitive energy range with the ETCC from 0.2–2.1 MeV in the previous studies to up to 3.5 MeV. Adjusting the PSA dynamic range should improve the sensitivity in even higher energy gamma-rays. The development of this new analysis method would pave the way for future observations by ETCC to fill the MeV-band sensitivity gap in astronomy.

Optical and radiation attenuation properties of rare-earth ion doped Li2O–ZnO–B2O3 glasses

The role of the addition of rare-earth ions which are Pr2O3, N2O3, Sm2O3, and Eu2O3 to Li2O–ZnO–B2O3 glasses on the optical and radiation attenuation characteristics was theoretically investigated. According to the addition of the rare-earth ions, the glasses were named as LZB, LZBPr, LZBNd, LZBSm and LZBEu. The LZB glass has the greatest molar refractivity and the molar polarizability whereas LZBPr glass has the lowest molar refractivity and the molar polarizability. The reflection loss is the highest for the LZB and the optical transmission is the highest for LZBEu. Especially, at higher gamma-ray energy (5–15 MeV), the linear attenuation coefficients are the greatest for LZBPr and they are the lowest for LZB. The LZBPr has the lowest half value layer, tenth value layer and mean free path at 10 MeV gamma-ray energy. At higher gamma-ray energies, LZBPr has the better radiation protection efficiency. Consequently, the LZBPr glass has the superior radiation attenuation ability and the addition of rare-earth ions to LZB glass enhances radiation shielding ability of the studied glasses.

Gamma shielding ability of Bismuth-Tungsten oxide (Bi[formula omitted]O[formula omitted]W) nanoparticles

Exposure to high energy radiations like X/gamma rays and neutrons is of serious concern for radiation professionals as they result in several radiation hazards. Shielding plays a prominent role in reducing the radiation exposure. Attempts are being made by several researchers to explore a novel material which can effectively absorb high energy radiations and find a best substitute for lead which is known to be heavy and toxic. In the present study, authors have attempted to synthesize a novel material and investigate the radiation shielding ability and structural properties of Bi2O6W nanomaterial. Bi2O6W nanomaterial has been synthesized for the first time using green synthesis approach in order to have environmental friendly material. SEM, XRD & FTIR techniques were used to investigate the physical & chemical structure and gamma ray spectrometer to study the gamma shielding ability of the said material. The XRD results reveal single crystal structure of the material. The mass attenuation coefficient was found to decrease with increase in photon energy due to the interaction of photons with the nanomaterial. The mass attenuation coefficient is found to be 0.127 ± 0.017, 0.142 ± 0.02, 0.106 ± 0.015,0.090 ± 0.013, 0.089 ± 0.013 and 0.094 ± 0.014 cm2/g for 0.276, 0.365, 0.511, 0.662, 1.173 and 1.332 MeV gamma rays respectively. The radiation protection efficiency is found to be high in lower energy range when compared to higher energy range of gamma photons. Thus, the newly synthesized nanomaterial can be used for shielding of X/Gamma radiations in the radiation environment thus proving its efficiency in low energy shielding applications like medical field.

A Silicon-Photo-Multiplier-Based Camera for the Terzina Telescope on Board the Neutrinos and Seismic Electromagnetic Signals Space Mission

NUSES is a pathfinder satellite project hosting two detectors: Ziré and Terzina. Ziré focuses on the study of protons and electrons below 250 MeV and MeV gamma rays. Terzina is dedicated to the detection of Cherenkov light produced by ultra-high-energy cosmic rays above 100 PeV and ultra-high-energy Earth-skimming neutrinos in the atmosphere, ensuring a large exposure. This work mainly concerns the description of the Cherenkov camera, composed of SiPMs, for the Terzina telescope. To increase the data-taking period, the NUSES orbit will be Sun-synchronous (with a height of about 550 km), thus allowing Terzina to always point toward the dark side of the Earth’s limb. The Sun-synchronous orbit requires small distances to the poles, and as a consequence, we expect an elevated dose to be received by the SiPMs. Background rates due to the dose accumulated by the SiPM would become a dominant contribution during the last two years of the NUSES mission. In this paper, we illustrate the measured effect of irradiance on SiPM photosensors with a variable-intensity beam of 50 MeV protons up to a 30 Gy total integrated dose. We also show the results of an initial study conducted without considering the contribution of solar wind protons and with an initial geometry with Geant4. The considered geometry included an entrance lens as one of the options in the initial design of the telescope. We characterize the SiPM output signal shape with different μ-cell sizes. We describe the developed parametric SiPM simulation, which is a part of the full Terzina simulation chain.

Sub-GeV Gamma Rays from Nearby Seyfert Galaxies and Implications for Coronal Neutrino Emission

Recent observations of high-energy neutrinos by IceCube and gamma rays by the Fermi Large Area Telescope (LAT) and the MAGIC telescope have suggested that neutrinos are produced in gamma-ray opaque environments in the vicinity of supermassive black holes. In this work, we present 20 MeV–1 TeV spectra of three Seyfert galaxies whose nuclei are predicted to be active in neutrinos, NGC 4151, NGC 4945, and the Circinus galaxy, using 14.4 yr of Fermi LAT data. In particular, we find evidence of sub-GeV excess emission that can be attributed to gamma rays from NGC 4945, as was also seen in NGC 1068. These spectral features are consistent with predictions of the magnetically powered corona model, and we argue that NGC 4945 is among the brightest neutrino active galaxies detectable for KM3Net and Baikal-GVD. On the other hand, in contrast to other reported results, we do not detect gamma rays from NGC 4151, which constrains neutrino emission from the accretion shock model. Future neutrino detectors such as IceCube-Gen2 and MeV gamma-ray telescopes such as AMEGO-X will be crucial for discriminating among the theoretical models.