High Energy Gamma-ray Research Articles

Testing the molecular cloud paradigm for ultra-high-energy gamma ray emission from the direction of SNR G106.3+2.7

Context. Supernova remnants (SNRs) are believed to be capable of accelerating cosmic rays (CRs) to PeV energies. SNR G106.3+2.7 is a prime PeVatron candidate. It is formed by a head region, where the pulsar J2229+6114 and its boomerang-shaped pulsar wind nebula are located, and a tail region containing SN ejecta. The lack of observed gamma ray emission from the two regions of this SNR has made it difficult to assess which region would be responsible for the PeV CRs. Aims. We aim to characterize the very-high-energy (VHE, 0.1–100 TeV) gamma ray emission from SNR G106.3+2.7 by determining the morphology and spectral energy distribution of the region. This is accomplished using 2565 days of data and improved reconstruction algorithms from the High Altitude Water Cherenkov (HAWC) Observatory. We also explore possible gamma ray production mechanisms for different energy ranges. Methods. Using a multi-source fitting procedure based on a maximum-likelihood estimation method, we evaluate the complex nature of this region. We determine the morphology, spectrum, and energy range for the source found in the region. Molecular cloud information is also used to create a template and evaluate the HAWC gamma ray spectral properties at ultra-high-energies (UHE, > 56 TeV). This will help probe the hadronic nature of the highest-energy emission from the region. Results. We resolve one extended source coincident with all other gamma ray observations of the region. The emission reaches above 100 TeV and its preferred log-parabola shape in the spectrum shows a flux peak in the TeV range. The molecular cloud template fit on the higher energy data reveals that the SNR’s energy budget is fully capable of producing a purely hadronic source for UHE gamma rays. Conclusions. The HAWC observatory resolves one extended source between the head and the tail of SNR G106.3+2.7 in the VHE gamma ray regime. The template fit suggests the highest energy gamma rays could come from a hadronic origin. However, the leptonic scenario, or a combination of the two, cannot be excluded at this time.

High-contrast Compton camera: Challenges to high-quality and broadband imaging

In the field of nuclear medicine, various radiopharmaceuticals require wideband x-ray/gamma-ray imaging devices for clinical and treatment monitoring. Compton cameras, which perform imaging using high-energy gamma rays, have the potential to significantly increase the variety of radioactive nuclides that can be imaged. However, artifacts caused by the so-called “Compton cone” have hindered their clinical use. Therefore, we propose the use of a collimator to improve the contrast of images obtained using Compton cameras. In this study, we developed a high-contrast Compton camera by attaching a tungsten collimator to its front surface. The contrast is improved by applying weighting to the signals based on the distance that the high-energy gamma rays penetrated the collimator walls. As a demonstration, we visualized 198Au plates that emit 412-keV gamma rays with and without the collimator. In addition, low-energy (<200 keV) x-ray/gamma-ray imaging, which is difficult for conventional Compton cameras, was achieved by performing single-photon emission computed tomography (SPECT) using the collimator and scatterer of the Compton camera. We demonstrated broadband gamma-ray imaging by visualizing a 133Ba standard source using 81-keV and 356-keV gamma rays based on the principles of SPECT and Compton cameras, respectively.

New high-precision measurement system for electron–positron pairs from sub-GeV/GeV gamma-rays in the emulsion telescope

The GRAINE project observes cosmic gamma-rays, using a balloon-borne emulsion-film-based telescope in the sub-GeV/GeV energy band. We reported in our previous balloon experiment in 2018, GRAINE2018, the detection of the known brightest source, Vela pulsar, with the highest angular resolution ever reported in an energy range of >80MeV. However, the emulsion scanning system used in the experiment was designed to achieve a high-speed scanning, and it was not accurate enough to ensure the optimum spatial resolution of the emulsion film and limited the performance. Here, we report a new high-precision scanning system that can be used to greatly improve the observation result of GRAINE2018 and also be employed in future experiments. The scanning system involves a new algorithm that recognizes each silver grain on an emulsion film and is capable of measuring tracks with a positional resolution for the passing points of tracks of almost the same as the intrinsic resolution of nuclear emulsion film (∼70 nm). This resolution is approximately one order of magnitude smaller than that obtained with the high-speed scanning system. With this scanning system, an angular resolution for gamma-rays of 0.1° at 1GeV is expected to be achieved. Furthermore, we successfully combine the new high-precision scanning system with the existing high-speed scanning system, enabling the high-speed and high-precision measurements. Employing these techniques, we reanalyze the gamma-ray events detected previously by only the high-speed scanning system in GRAINE2018 and obtain an about three times higher angular resolution (0.22°) in the 500–700MeV energy range. Adopting this technique in future observations may provide new insights into the gamma-ray emission from the Galactic center region and may realize polarization measurements of high-energy cosmic gamma-rays.

Multiwavelength Galactic center gamma-ray observations explained by a unified cosmic-ray dynamics model

Context. High-energy (HE) and very high-energy (VHE) gamma-ray observations from the Galactic center (GC) detected extended emission correlated with the morphology of the central molecular zone (CMZ). Emission in both bands is expected to be produced by hadronic interaction between cosmic rays (CRs) and ambient gas. Aims. We examine if our three previously proposed scenarios for the CR sources and dynamics, which are consistent with the VHE gamma-ray data (1–100 TeV), also match the HE gamma-ray observations (10–300 GeV). Additionally, we analyze the effect of the isotropic Galactic CR “sea” inside the CMZ. Methods. We generated synthetic gamma-ray maps considering a simplified isotropic diffusion, but more realistic dynamics with two diffusion zones (in and out of the CMZ) and polar advection, for mono-energetic particles of 3 TeV. Additionally, we considered two gas distributions for the CMZ (with and without an inner cavity), and CR populations injected from the clusters of young massive stars (the Arches Cluster, the Quintuplet Cluster, and the nuclear star cluster), plus the supernova Sgr A East. Results. Only the combination of more realistic CR dynamics, the CMZ with an inner cavity, CR injection from all proposed sources, and a CR sea similar to that observed in the Solar System reproduced the current HE and VHE gamma-ray detection from the CMZ and was consistent with the observed gamma-rays from Sagittarius A*. Conclusions. The HE and VHE gamma-rays observations of the GC can be reproduced by a unified model for the CRs.

Origin of the Very High Energy Gamma Rays in the Low-luminosity Active Galactic Nucleus NGC 4278

NGC 4278, a low-luminosity active galactic nucleus, is generally classified as a low-ionization nuclear emission-line region (LINER). Recently, it has been reported to be associated with a very high energy γ-ray source 1LHAASO J1219+2915 in the first Large High Altitude Air Shower Observatory source catalog. However, no associated counterpart has been detected by analyzing the data collected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. By analyzing its X-ray observation data from Swift-XRT, we find that NGC 4278 is in a high-flux state on MJD 59546, with the X-ray flux more than one order of magnitude higher than that observed ∼11.7 yr earlier by Chandra. Interestingly, this Swift-XRT observation was conducted during the active phase of the γ-ray source 1LHAASO J1219+2915. We propose that the detection of very high energy γ-rays from NGC 4278 may be attributed to the presence of an active nucleus in its center. To reproduce the spectral energy distribution (SED) of NGC 4278, we employ a one-zone leptonic model, typically used for fitting broadband SEDs of BL Lacs, and find that a smaller magnetic field strength is required than that of typical TeV BL Lacs. Furthermore, NGC 4278 exhibits significantly lower luminosity in both radio and TeV bands when compared with typical TeV BL Lacs. In the radio luminosity versus Eddington ratio plane, NGC 4278 shows greater similarity to Seyfert galaxies and LINERs than to BL Lacs; however, it still roughly follows the extension toward lower luminosity seen in BL Lacs.

Search for the Hawking radiation of primordial black holes: prospective sensitivity of LHAASO

Primordial black holes (PBHs), more generally, BHs, undergo evaporation and, in principle, will end their lives in bursts of very high-energy gamma rays. The notable aspect of the PBHs with an initial mass of ∼ 1014 g is that they are expected to end their lives today. In this work, we assess the potential sensitivity of the Large High Altitude Air Shower Observatory (LHAASO) in detecting the local burst rate density of PBHs. Our results suggest that LHAASO is capable of probing for PBH bursts within a proximity of ∼ 0.1 pc from the Sun, measuring a local burst rate density of ∼ 1200 (or 700)pc-3 yr-1 with 99% confidence during a 3-year (or 5-year) observational campaign. This level of sensitivity surpasses the most rigorous observational constraint provided by the High Altitude Water Cherenkov Observatory (HAWC) by an order of magnitude. Additionally, we propose data analysis strategies for LHAASO to optimize the search for PBHs and reach its potential detection limits.

Implications of the Spin-Induced Accretion Disk Truncation on the X-ray Binary Broadband Emission

Black hole X-ray binary systems consist of a black hole accreting mass from its binary companion, forming an accretion disk. As a result, twin relativistic plasma ejections (jets) are launched towards opposite and perpendicular directions. Moreover, multiple broadband emission observations from X-ray binary systems range from radio to high-energy gamma rays. The emission mechanisms exhibit thermal origins from the disk, stellar companion, and non-thermal jet-related components (i.e., synchrotron emission, inverse comptonization of less energetic photons, etc.). In many attempts at fitting the emitted spectra, a static black hole is often assumed regarding the accretion disk modeling, ignoring the Kerr metric properties that significantly impact the geometry around the usually rotating black hole. In this work, we study the possible implications of the spin inclusion in predictions of the X-ray binary spectrum. We mainly focus on the most significant aspect inserted by the Kerr geometry, the innermost stable circular orbit radius dictating the disk’s inner boundary. The outcome suggests a higher-peaked and hardened X-ray spectrum from the accretion disk and a substantial increase in the inverse Compton component of disk-originated photons. Jet-photon absorption is also heavily affected at higher energy regimes dominated by hadron-induced emission mechanisms. Nevertheless, a complete investigation requires the full examination of the spin contribution and the resulting relativistic effects beyond the disk truncation.

Design and test of an X -band constant gradient structure

A light source project named very compact inverse Compton scattering gamma-ray source (VIGAS) is under development at Tsinghua University. VIGAS aims to generate monochromatic high-energy gamma rays by colliding 350-MeV electron beams with 400-nm laser photons within a 12-m beamline. To produce a high-energy electron beam in such a compact space, the system consists of an S-band high-brightness injector and six X-band high-gradient accelerating structures. The goal of the X-band structure is to operate at a high gradient of 80 MV/m. Therefore, we adopts the constant gradient traveling wave approach, where the iris from the first cell to the end cell is tapered. The structure has 72 cells, including 70 cells and 2 couplers, so we named it XT72. The frequency of XT72 is selected to 11.424 GHz, and the 2π/3 mode is adopted. In this paper, we present a comprehensive study covering the detailed design, fabrication, rf tuning, and high-power test results of the first XT72. Additionally, we compare the performance of this structure to that of the previous constant impedance structure. Our results demonstrate that the XT72 is capable of operating at an 80−MV/m gradient with a lower breakdown rate. This advancement paves the way for the development of VIGAS project and contributes to the wider application of X-band room-temperature high-gradient structures in compact accelerator facilities. Published by the American Physical Society 2024

Galactic Stellar Black Hole Binaries: Spin Effects on Jet Emissions of High-Energy Gamma-Rays

In the last few decades, galactic stellar black hole X-ray binary systems (BHXRBs) have aroused intense observational and theoretical research efforts specifically focusing on their multi-messenger emissions (radio waves, X-rays, γ-rays, neutrinos, etc.). In this work, we investigate jet emissions of high-energy neutrinos and gamma-rays created through several hadronic and leptonic processes taking place within the jets. We pay special attention to the effect of the black hole’s spin (Kerr black holes) on the differential fluxes of photons originating from synchrotron emission and inverse Compton scattering and specifically on their absorption due to the accretion disk’s black-body radiation. The black hole’s spin (dimensionless spin parameter a*) enters into the calculations through the radius of the innermost circular orbit around the black hole, the RISCO parameter, assumed to be the inner radius of the accretion disk, which determines its optical depth τdisk. In our results, the differential photon fluxes after the absorption effect are depicted as a function of the photon energy in the range 1GeV ≤E≤103GeV. It is worth noting that when the black holes’ spin (α*) increases, the differential photon flux becomes significantly lower.

Detection prospects of very and ultra high-energy gamma rays from extended sources with ASTRI, CTA, and LHAASO

Context. The recent discovery of several ultra high-energy gamma-ray emitters in our Galaxy represents a significant advancement towards the characterisation of its most powerful accelerators. Nonetheless, in order to unambiguously locate the regions where the highest energy particles are produced and understand the responsible physical mechanisms, detailed spectral and morphological studies are required, especially given that most of the observed sources were found to be significantly extended. Aims. In these regards, pointing observations with the next-generation Imaging Atmospheric Cherenkov Telescopes, such as the Cherenkov Telescope Array (CTA) Observatory and the ASTRI Mini-Array (ASTRI), are expected to provide significant improvements. Here we aim to identify the most promising sources to target in future observations. Methods. For this purpose, we performed a comparative analysis of the expected performance of ASTRI and CTA, computing their differential sensitivities towards extended sources, and further explored their capabilities with respect to specific case studies, including follow-ups of existing gamma-ray source catalogues. Results. We find that almost all of the sources thus far detected by LHAASO-WCDA and in the H.E.S.S. Galactic Plane Survey will be in the reach of ASTRI and CTA with about 300 and 50 hours of exposure, respectively. For the highest energy emitters detected by LHAASO-KM2A, in turn, we provide a list of the most promising objects that would require further investigation. We additionally examined specific classes of sources in order to identify potentially detectable gamma-ray emitters, such as passive molecular clouds (i.e. illuminated by the cosmic-ray sea) and pulsars surrounded by a halo of runaway particles.

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.

Results of the follow-up of ANTARES neutrino alerts

High-energy neutrinos could be produced in the interaction of charged cosmic rays with matter or radiation surrounding astrophysical sources. To look for transient sources associated with neutrino emission, a follow-up program of neutrino alerts has been operating within the ANTARES collaboration since 2009. This program, named TAToO, has triggered robotic optical telescopes (MASTER, TAROT, ROTSE and the SVOM ground based telescopes) immediately after the detection of any relevant neutrino candidate and scheduled several observations in the weeks following the detection. A subset of ANTARES events with highest probabilities of being of cosmic origin has also been followed by the Swift and the INTEGRAL satellites, the Murchison Widefield Array radio telescope and the H.E.S.S. high-energy gamma-ray telescope. The results of twelve years of observations are reported. In September 2015, ANTARES issued a neutrino alert and during the follow-up, a potential transient counterpart was identified by Swift and MASTER. A multi-wavelength follow-up campaign has allowed to identify the nature of this source and has proven its fortuitous association with the neutrino. No other optical and X-ray counterpart has been significantly associated with an ANTARES candidate neutrino signal. Constraints on transient neutrino emission have been set. The return of experience is particularly important for the design of the alert system of KM3NeT, the next generation neutrino telescope in the Mediterranean Sea.

Discovery of Very High Energy Gamma-Ray Emissions from the Low-luminosity AGN NGC 4278 by LHAASO

Abstract The first source catalog of the Large High Altitude Air Shower Observatory (LHAASO) reported the detection of a very high energy gamma-ray source, 1LHAASO J1219+2915. This Letter presents a further detailed study of the spectral and temporal behavior of this pointlike source. The best-fit position of the TeV source (R.A. = 185.°05 ± 0.°04, decl. = 29.°25 ± 0.°03) is compatible with NGC 4278 within ∼0.°03. Variation analysis shows an indication of variability on a timescale of a few months in the TeV band, which is consistent with low-frequency observations. Based on these observations, we report the detection of TeV γ-ray emissions from this low-luminosity active galactic nucleus. The observation by LHAASO's Water Cherenkov Detector Array during the active period has a significance level of 8.8σ with a best-fit photon spectral index Γ = 2.56 ± 0.14 and a flux f 1–10 TeV = (7.0 ± 1.1sta ± 0.35syst) × 10−13 photons cm−2 s−1, or approximately 5% of the Crab Nebula. The discovery of VHE gamma-ray emission from NGC 4278 indicates that compact, weak radio jets can efficiently accelerate particles and emit TeV photons.

Implications of gamma ray burst GRB221009A for extra dimensions

Anomalous high-energy photons from GRB221009A, with energies of 18 TeV and 251 TeV, were observed by LHAASO and Carpet-2 recently. Such observation of high energy gamma-ray bursts from distant source causes a mystery since high energy photons suffer severe attenuation before reaching the earth. One possibility is the existence of axion-like particles (ALP), and high energy photons at the source can convert to these ALPs which travel intergalactically. In this paper, we study the effects of extra dimensions on the conversion probability between photon and ALPs. The conversion probability saturates and may reach almost 100% for high energy photons. We show that the size of extra dimension affects the energy at which saturation occurs. The observations of high-energy photons may support the possibility of smaller extra dimension.

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.

Sensitivity to sub-GeV dark matter from cosmic-ray scattering with very-high-energy gamma-ray observatories

Huge efforts have been deployed to detect dark matter (DM) in the GeV-TeV mass range involving various detection techniques, and led to strong constraints in the available parameter space. We compute here the sensitivity to sub-GeV DM that can be probed from the inevitable cosmic-ray scattering onto DM particles populating the Milky Way halo. Inelastic scattering of energetic cosmic rays off DM would produce high-energy gamma rays in the final state, providing a new avenue to probe the poorly-constrained so far sub-GeV dark matter mass range. In this work we derivesensitivity forecasts for the inelastic cosmic-ray proton-DM cross section for current and future very-high-energy gamma-ray observatories such as H.E.S.S., LHAASO, CTA and SWGO in the 100 eV to 100 MeV mass range. These inelastic cross section constraints are converted to the elastic proton-DM cross sectionto highlight further complementarity with cosmological, collider and direct detection searches.The sensitivity computed at 95% confidence level on the elastic cross section reaches ∼2 × 10-32 cm2 for a 100 keV DM mass for H.E.S.S.-like and ∼7 × 10-34 cm2 for a ∼1 keV DM mass for LHAASO. The sensitivity prospects for CTA and a strawman SWGO model reach ∼6 × 10-34 cm2 and ∼4 × 10-35 cm2, for DM masses of 10 keV and 1 keV, respectively. The sensitivity reach of the gamma-ray observatories considered here enables to probe an uncharted region of the DM mass-cross section parameter space.

Studying the role of supernova remnants as cosmic ray PeVatron with LHAASO observations

It is commonly believed that galactic cosmic rays are produced in supernova remnants (SNRs) and accelerated via a diffusive shock acceleration (DSA) mechanism in supernova blast waves driven by expanding SNRs. The latest theoretical advancement of the diffusive shock acceleration hypothesis in SNRs shows that cosmic rays may be accelerated up to the knee energy of the observed cosmic ray spectrum under the amplified magnetic field scenario. There is, however, no empirical evidence to support SNRs as sources of hadrons with energies larger than a few tens of TeV. Very recently, LHAASO observatory reported the very high-energy gamma ray emission between TeV to PeV energy range from two SNRs, Cassiopeia A and IC 443. Above 25 TeV energies, non-detection of gamma-ray flux by LHAASO yields a strong upper limit. In this work, we investigate the implications of the acceleration of cosmic ray protons in the SNR on energetic gamma rays produced in the hadronic interaction of cosmic rays with ambient matter. Our findings imply that when we consider the highest attainable energy of cosmic ray protons in the SNRs to be about 100 TeV, the observed gamma-ray spectra from the two SNRs can be described consistently. Therefore, we conclude that the Cassiopia A and IC 443 SNRs are unlikely to be cosmic ray PeVatrons.

Influence of cosmic voids on the propagation of TeV gamma-rays and the puzzle of GRB 221009A

ABSTRACT The recent detection of gamma-ray burst GRB 221009A has attracted attention due to its record brightness and first-ever detection of $\gtrsim 10$ TeV gamma-rays from a GRB. Despite being the second-nearest GRB ever detected, at a redshift of $z=0.151$, the distance is large enough for severe attenuation of gamma-ray flux at these energies due to $\gamma \gamma \rightarrow e^\pm$ pair production with the extragalactic background light (EBL). Here, we investigate whether the presence of cosmic voids along the line of sight can significantly impact the detectability of very high energy (VHE, $\gt $100 GeV) gamma-rays from distant sources. Notably, we find that the gamma–gamma opacity for VHE gamma-rays can be reduced by approximately 10 per cent and up to 30 per cent at around 13 TeV, the highest-energy photon detected from GRB 221009A, for intervening cosmic voids along the line of sight with a combined radius of 110 Mpc, typically found from void catalogues, and 250 Mpc, respectively. This reduction is substantially higher for TeV photons compared to GeV photons, attributable to the broader target photon spectrum that TeV photons interact with. This finding implies that VHE photons are more susceptible to variations in the EBL spectrum, especially in regions dominated by cosmic voids. Our study sheds light on the detection of $\gtrsim 10$ TeV gamma-rays from GRB 221009A in particular, and on the detection of extragalactic VHE sources in general.

Galaxy group-associated distances to very high energy gamma-ray emitting BL Lacs KUV 00311−1938 and S2 0109+22

ABSTRACT Blazars constitute the most numerous source class in the known extragalactic population of very high energy (VHE) gamma-ray sources. However, determining their redshifts is often challenging due to weak or non-existent emission lines in their spectra. This study focuses on two BL Lacs, KUV 00311−1938 and S2 0109+22, where previous attempts at redshift determination have faced difficulties. By combining spectroscopic observations with photometric redshift estimates, we tentatively assign a redshift of $z=0.634$ to KUV 00311−1938 and a likely redshift of $z=0.49$ to S2 0109+22. Establishing redshift estimates for high-redshift blazars is crucial for understanding extragalactic VHE gamma-ray sources and their interactions with the surrounding Universe.

Present and new operational quantities evaluated from photon spectrum measurements at workplaces in the research reactor and accelerator facility at the JAEA

The International Commission on Radiation Units and Measurements (ICRU) has proposed to change the definitions of the operational quantities used for the area and individual monitoring of external exposure in ICRU Report 95. Since introducing new operational quantities into the radiation monitoring may affect the dose assessment using the present personal dosimeters, precise assessments of the influence on monitoring are necessary by characterizing the energy spectrum in the workplace and the energy dependency of the dosimeters to be used. This study measured photon spectra using a NaI(Tl) scintillation detector or a LaBr3(Ce) scintillation detector at the Japan Research Reactor No. 3 (JRR-3) and Japan Proton Accelerator Research Complex (J-PARC) workplaces at the Japan Atomic Energy Agency (JAEA). The photon energy spectra were obtained by unfolding the pulse height distributions measured at each workplace. The present and new operational quantities were then evaluated and compared using the spectra measured at the workplaces.In JRR-3, the photon energy spectra were measured at the workplaces in the reactor room and thermal neutron beam hall while the reactor was operated. The ambient dose equivalent rates H˙*(10) at the workplaces were 0.2 μSv·h−1 – 13 μSv·h−1. High energy gamma-rays of 6–7 MeV from 16N were observed near the fuel failure detection system in the reactor room. Those of 7–8 MeV produced by the thermal neutron capture of iron were observed in the reactor room and the beam hall. In J-PARC, the photon energy spectra were measured at the workplaces in the beam tunnel of the 3 GeV synchrotron beam ring five days after the operation. The ambient dose equivalent rates H˙*(10) at the workplaces were 35 μSv·h−1 –430 μSv·h−1.It was found that the new personal doses, Hp, were 10%–20% smaller than the present personal dose equivalents, Hp(10), at the workplaces.