Gamma-ray Background Radiation Research Articles

Annual gamma-ray background dose rates in dwellings of rural Tumkur.

The exposure to high levels of ionising radiation can cause severe health risks including cancer. The monitoring of background radiation is a primary task of nuclear scientists and researchers in the present day. The aim of the present work is to measure effective annual dose rate due to gamma-ray background radiation in dwellings of selected villages around Tumkur. It is very important to monitor background radiation in dwellings to safeguard from the harmful effects of gamma-ray background radiation. The dose rates in dwellings were measured using a German-made portable gamma dosemeter, Gamma-Scout. The measured annual dose rates were in the range of 1.103-2.824mSv/y. From this survey, it was observed that the average annual dose rate for dwellings under study area with concrete ceiling and tiles floor are comparatively higher than the dwellings with griddle ceiling and stone floor.

Cosmological Evolution of Flat-spectrum Radio Quasars Based on the Swift/BAT 105 Month Catalog and Their Contribution to the Cosmic MeV Gamma-Ray Background Radiation

Abstract We present a new X-ray luminosity function of flat-spectrum radio quasars (FSRQs) utilizing the latest Swift/BAT 105 month X-ray source catalog. Contrary to previous studies of FSRQs in the X-ray band, using the luminosity-dependent density evolution model we find that FSRQs show evolutionary peaks at z ∼ 1−2 depending on luminosities. Our result is rather consistent with the evolution of FSRQs seen in the radio and GeV bands, although the number density is a factor of 5–10 smaller. We further explore the contribution of FSRQs to the cosmic MeV gamma-ray background radiation. We find that FSRQs can explain only ∼3% of the observed MeV gamma-ray background fluxes around 1 MeV, indicating other populations are required. Future MeV gamma-ray observations will be keys for understanding the origin of the MeV gamma-ray background radiation.

A compact MPPC-based camera for omnidirectional (4π) fast-neutron imaging based on double neutron–proton elastic scattering

Abstract Neutron localization, which finds (localizes) neutron sources , is a non-destructive method used in the application of nuclear emergency response and special nuclear material (SNM) localization. Fast neutrons from SNM fission can be detected using a hydrogen-rich scintillation detector system with relatively high efficiency. In this study, we proposed a compact multi-pixel photon counter (MPPC)-based neutron scattering camera prototype consisting of sixteen plastic scintillator pillars. This camera is capable of detecting fast neutrons produced by neutron sources in the far-field. It provides a three-dimensional structure to detect incident neutrons with omnidirectional (4 π ) field-of-view. Based on double neutron–proton elastic scattering, a reconstructed image can be achieved by using an Am–Be source. Besides, time-of-flight technology was adopted for separating neutron signals from the gamma-ray background radiation. The results of the imaging efficiency and the average imaging resolution are reported in this article. This camera offers good prospects to expand the application field of SNM localization for nuclear security and proliferation deterrence.

Detection of Coronal Magnetic Activity in nearby Active Supermassive Black Holes

Abstract Central supermassive black holes of active galactic nuclei host hot plasma with a temperature of 109 K, namely coronae. Like the Sun, black hole coronae are theoretically believed to be heated by their magnetic activity, which have not been observed yet. Here we report the detection of coronal radio synchrotron emission from two nearby Seyfert galaxies using the Atacama Large Millimeter/submillimeter Array, the Karl G. Jansky Very Large Array, and Australia Telescope Compact Array. The coronal magnetic field of both systems is estimated to be ∼10 G on scales of ∼40 Schwarzschild radii from the central black holes. This magnetic field strength is weaker than the prediction from the magnetically heated corona scenario. We also find that coronae of Seyferts are composed of both thermal and nonthermal electrons. This may imply a possible contribution of Seyferts to the cosmic MeV gamma-ray background radiation.

High energy gamma rays from nebulae associated with extragalactic microquasars and ultra-luminous X-ray sources

In the extragalactic sky, microquasars and ultra-luminous X-ray sources (ULXs) are known as energetic compact objects locating at off-nucleus positions in galaxies. Some of these objects are associated with expanding bubbles with a velocity of 80–250 kms−1. We investigate the shock acceleration of particles in those expanding nebulae. The nebulae having fast expansion velocity ≳120kms−1 are able to accelerate cosmic rays up to ∼100 TeV. If 10% of the shock kinetic energy goes into particle acceleration, powerful nebulae such as the microquasar S26 in NGC 7793 would emit gamma rays up to several tens TeV with a photon index of ∼2. These nebulae will be good targets for future Cherenkov Telescope Array observations given its sensitivity and angular resolution. They would also contribute to ∼7% of the unresolved cosmic gamma-ray background radiation at ≥ 0.1 GeV. In contrast, particle acceleration in slowly expanding nebulae ≲120kms−1 would be less efficient due to ion-neutral collisions and result in softer spectra at ≳ 10 GeV.

A common solution of two cosmic puzzles

We show that the properties of the background of astronomical neutrinos above 30 TeV, which was discovered with IceCube, are those expected from the all sky high-energy gamma-ray background radiation (GBR), which was measured below 2 TeV with Fermi-LAT, if both backgrounds were formed by the decay of mesons produced in hadronic collisions of the high energy cosmic rays (CRs) with diffuse matter in/near the CR sources.

LOWER BOUND ON THE COSMIC TeV GAMMA-RAY BACKGROUND RADIATION

ABSTRACT The Fermi gamma-ray space telescope has revolutionized our understanding of the cosmic gamma-ray background radiation in the GeV band. However, investigation on the cosmic TeV gamma-ray background radiation still remains sparse. Here, we report the lower bound on the cosmic TeV gamma-ray background spectrum placed by the cumulative flux of individual detected extragalactic TeV sources including blazars, radio galaxies, and starburst galaxies. The current limit on the cosmic TeV gamma-ray background above 0.1 TeV is obtained as 2.8 × 10−8(E/100 GeV)−0.55 exp(−E/2100GeV)[GeV cm−2 s−1 sr−1] < E 2 dN/dE < 1.1 × 10−7(E/100 GeV)−0.49 [GeV cm−2 s−1 sr−1], where the upper bound is set by requirement that the cascade flux from the cosmic TeV gamma-ray background radiation can not exceed the measured cosmic GeV gamma-ray background spectrum. Two nearby blazars, Mrk 421 and Mrk 501, explain ∼70% of the cumulative background flux at 0.8–4 TeV, while extreme blazars start to dominate at higher energies. We also provide the cumulative background flux from each population, i.e., blazars, radio galaxies, and starburst galaxies which will be the minimum requirement for their contribution to the cosmic TeV gamma-ray background radiation.

A determination of the gamma-ray flux and photon spectral index distributions of blazars from theFermi-LAT 3LAC

We present a determination of the distributions of gamma-ray photon flux – the so-called LogN–LogS relation – and photon spectral index for blazars, based on the third extragalactic source catalogue of the FermiGamma-ray Space Telescope's Large Area Telescope, and considering the photon energy range from 100 MeV to 100 GeV. The data set consists of the 774 blazars in the so-called Clean sample detected with a greater than approximately 7σ detection threshold and located above ±20° Galactic latitude. We use non-parametric methods verified in previous works to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation between the flux and photon index. The intrinsic flux distribution can be represented by a broken power law with a high-flux power-law index of −2.43 ± 0.08 and a low-flux power-law index of −1.87 ± 0.10. The intrinsic photon index distribution can be represented by a Gaussian with mean of 2.62 ± 0.05 and width of 0.17 ± 0.02. We also report the intrinsic distributions for the subpopulations of BL Lac and FSRQ (Flat Spectrum Radio Quasar)-type blazars separately and these differ substantially. We then estimate the contribution of FSRQs and BL Lacs to the diffuse extragalactic gamma-ray background radiation. Under the simplistic assumption that the flux distributions probed in this analysis continue to arbitrary low flux, we calculate that the best-fitting contribution of FSRQs is 35 per cent and BL Lacs 17 per cent of the total gamma-ray output of the Universe in this energy range.

Prospect for future MeV gamma-ray active galactic nuclei population studies

Abstract While the X-ray, GeV gamma-ray, and TeV gamma-ray skies have been extensively studied, the MeV gamma-ray sky has not yet been well investigated since the Imaging Compton Telescope (COMPTEL) scanned the sky about two decades ago. In this paper, we investigate the prospects for active galactic nuclei population studies with future MeV gamma-ray missions using recent spectral models and luminosity functions of Seyferts and flat-spectrum radio quasars (FSRQs). Both of them are plausible candidates for the origins of the cosmic MeV gamma-ray background. If the cosmic MeV gamma-ray background radiation is dominated by non-thermal emission from Seyferts, a sensitivity of 10−12 erg cm−2 s−1 is required to detect several hundred Seyferts in the entire sky. If FSRQs make up the cosmic MeV gamma-ray background, a sensitivity of ∼ 4 × 10−12 erg cm−2 s−1 is required to detect several hundred FSRQs following the recent FSRQ X-ray luminosity function. However, based on the latest FSRQ gamma-ray luminosity function, with which FSRQs can explain up to ∼ 30% of the MeV background, we can expect several hundred FSRQs even with a sensitivity of 10−11 erg cm−2 s−1, which is almost the same as the sensitivity goal of the next-generation MeV telescopes.

5D World-Universe Model. Multicomponent Dark Matter

5D World-Universe Model (WUM) is based on the decisive role of the Medium of the World com-posed of massive particles: protons, electrons, photons, neutrinos, and Dark Matter Particles (DMP). The model forecasts the masses of DMP, discusses the possibility of all macroobject cores consisting of DMP (galaxy clusters, galaxies, star clusters, extrasolar systems, and planets), and explains the diffuse cosmic gamma-ray background radiation as the sum of contributions of multicomponent dark matter annihilation. The signatures of DMP annihilation with expected masses of 1.3 TeV, 9.6 GeV, 70 MeV, 340 keV, and 3.7 keV, are found in spectra of the diffuse gamma-ray background and the emission of various macroobjects in the World. The correlation between different emission lines in spectra of macroobjects is connected to their structure, which depends on the composition of the cores and surrounding shells made up of DMP. Consequently, the diversity of Very High Energy (VHE) gamma-ray sources in the World has a clear explanation.

GAMMA-RAY LUMINOSITY AND PHOTON INDEX EVOLUTION OF FSRQ BLAZARS AND CONTRIBUTION TO THE GAMMA-RAY BACKGROUND

We present the redshift evolutions and distributions of the gamma-ray luminosity and photon spectral index of flat spectrum radio quasar (FSRQ) type blazars, using non-parametric methods to obtain the evolutions and distributions directly from the data. The sample we use for analysis consists of almost all FSRQs observed with a greater than approximately 7 sigma detection threshold in the first year catalog of the Fermi Gamma-ray Space Telescope's Large Area Telescope, with redshfits as determined from optical spectroscopy by Shaw et al. We find that FSQRs undergo rapid gamma-ray luminosity evolution, but negligible photon index evolution, with redshift. With these evolutions accounted for we determine the density evolution and luminosity function of FSRQs, and calculate their total contribution to the extragalactic gamma-ray background radiation, resolved and unresolved, which is found to be 16(+10/-4)%, in agreement with previous studies.

Status of the JET Faraday cup lost alpha particle diagnostic KA-2

We review the operational status and present a few recent results from the JET lost alpha particle diagnostic KA2. We summarize the results of our study of the correlation between KA2 signals and JET magnetic fields and the correlation between KA2 signals and the scintillator-based lost alpha probe KA3. In addition we quantify the relative insensitivity of the diagnostic to intense neutron and gamma ray background radiation fields and our observations of the electro-mechanical noise in the diagnostics signals. We present recent observations carried out during the 2011 JET campaign following the installation of the beryllium ITER-like wall. These observations include lost energetic deuterons during both ion-cyclotron and neutral beam heated plasmas; in particular we have measured relatively intense fluxes of energetic particles during sawtooth plasmas.

FLUX AND PHOTON SPECTRAL INDEX DISTRIBUTIONS OFFERMI-LAT BLAZARS AND CONTRIBUTION TO THE EXTRAGALACTIC GAMMA-RAY BACKGROUND

We present a determination of the distributions of photon spectral index and gamma-ray flux - the so called LogN-LogS relation - for the 352 blazars detected with a greater than approximately seven sigma detection threshold and located above +/- 20 degrees Galactic latitude by the Large Area Telescope of the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true LogN-LogS counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation between the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law with high and low indexes of -2.37 +/- 0.13 and -1.70 +/- 0.26, respectively, and the intrinsic photon index distribution can be represented by a Gaussian with mean of 2.41 +/- 0.13 and width of 0.25 +/- 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and FSRQs type blazars separately. We then calculate the contribution of Fermi blazars to the diffuse extragalactic gamma-ray background radiation. Under the assumption that the flux distribution of blazars continues to arbitrarily low fluxes, we calculate the best fit contribution of all blazars to the total extragalactic gamma-ray output to be 60%, with a large uncertainty.

Extragalactic Gamma-ray Background Radiation from Beamed and Unbeamed Active Galactic Nuclei

The origin of the extragalactic gamma-ray background (EGRB) radiation has been a mystery in astrophysics for a long time. Recently the Fermi gamma-ray satellite (Fermi) has revealed that ∼22% of the unresolved EGRB would be explained by blazars, which are one population of beamed active galactic nuclei (AGNs). The remaining ∼78% of the unresolved EGRB is still unknown. We estimate the contribution of gamma-ray loud radio galaxies, which are misaligned radio loud AGNs recently detected by Fermi, to EGRB using the radio luminosity function of radio-loud AGNs with the correlation between the radio and gamma-ray luminosities. We find that ∼25% of the unresolved EGRB will be explained by gamma-ray loud radio galaxy population. We also discuss further about the origin of EGRB by comparing the Fermi EGRB data with our studies on various AGN populations' contribution to EGRB, which are radio quiet AGNs, blazars, and gamma-ray loud radio galaxies.

CONSTRAINING THE EMISSIVITY OF ULTRAHIGH ENERGY COSMIC RAYS IN THE DISTANT UNIVERSE WITH THE DIFFUSE GAMMA-RAY EMISSION

Ultra-high cosmic rays (UHECRs) with energies >10^19 eV emitted at cosmological distances will be attenuated by cosmic microwave and infrared background radiation through photohadronic processes. Lower energy extra-galactic cosmic rays (~10^18-10^19 eV) can only travel a linear distance smaller than ~Gpc in a Hubble time due to the diffusion if the extra-galactic magnetic fields are as strong as nano Gauss. These prevent us from directly observing most of the UHECRs in the universe, and thus the observed UHECR intensity reflects only the emissivity in the nearby universe within hundreds of Mpc. However, UHECRs in the distant universe, through interactions with the cosmic background photons, produce UHE electrons and gamma-rays that in turn initiate electromagnetic cascades on cosmic background photons. This secondary cascade radiation forms part of the extragalactic diffuse GeV-TeV gamma-ray radiation and, unlike the original UHECRs, is observable. Motivated by new measurements of extragalactic diffuse gamma-ray background radiation by Fermi/LAT, we obtained upper limits placed on the UHECR emissivity in the distant universe by requiring that the cascade radiation they produce not exceed the observed levels. By comparison with the gamma-ray emissivity of candidate UHECR sources (such as GRBs and AGNs) at high-redshifts, we find that the obtained upper limit for a flat proton spectrum is ~10^1.5 times larger than the gamma-ray emissivity in GRBs and ~10 times smaller than the gamma-ray emissivity in BL Lac objects. In the case of iron nuclei composition, the derived upper limit of the UHECR emissivity is a factor of 3-5 times higher. Robust upper limit on the cosmogenic neutrino flux is further obtained, which is marginally reachable by the Icecube detector and the next-generation detector JEM-EUSO.

CONTRIBUTION FROM STAR-FORMING GALAXIES TO THE COSMIC GAMMA-RAY BACKGROUND RADIATION

We present a new theoretical calculation of the contribution to the extragalactic gamma-ray background radiation (EGRB) from star-forming galaxies, based on a state-of-the-art model of hierarchical galaxy formation that is in quantitative agreement with a variety of observations of local and high-redshift galaxies. Gamma-ray luminosity ($L_\gamma$) and spectrum of galaxies are related to star formation rate ($\psi$), gas mass ($M_gas$), and star formation mode (quiescent or starburst) of model galaxies using latest observed data of nearby galaxies. We try the two limiting cases about gamma-ray production: the escape limit ($L_\gamma \propto \psi M_gas$) and the calorimetric limit ($L_\gamma \propto \psi$), and our standard model predicts 7 and 4% contribution from star-forming galaxies to the total EGRB flux (including bright resolved sources) recently reported by the Fermi Gamma-Ray Space Telescope. Systematic uncertainties do not allow us to determine the EGRB flux better than by a factor of ~2. The predicted number of nearby galaxies detectable by Fermi is consistent with the observation. Intergalactic absorption by pair-production attenuates the EGRB flux only by a modest factor of ~1.3 at the highest Fermi energy band, and the reprocessed cascade emission does not significantly alter EGRB at lower photon energies. The sum of the known contributions from AGNs and star-forming galaxies can explain a large part of EGRB, with a remarkable agreement between the predicted model spectrum and observation.

Extragalactic gamma-ray background radiation from dark matter annihilation

If dark matter is composed of neutralinos, one of the most exciting prospects for its detection lies in observations of the gamma-ray radiation created in pair annihilations between neutralinos, a process that may contribute significantly to the extragalactic gamma-ray background (EGB) radiation. We here use the high-resolution Millennium-II simulation of cosmic structure formation to produce the first full-sky maps of the expected radiation coming from extragalactic dark matter structures. Our map making procedure takes into account the total gamma-ray luminosity from all haloes and their subhaloes, and includes corrections for unresolved components of the emission as well as an extrapolation to the damping scale limit of neutralinos. Our analysis also includes a proper normalization of the signal according to a specific supersymmetric model based on minimal supergravity. The new simulated maps allow a study of the angular power spectrum of the gamma-ray background from dark matter annihilation, which has distinctive features associated with the nature of the annihilation process and may be detectable in forthcoming observations by the recently launched FERMI satellite. Our results are in broad agreement with analytic models for the gamma-ray background, but they also include higher-order correlations not readily accessible in analytic calculations and, in addition, provide detailed spectral information for each pixel. In particular, we find that difference maps at different energies can reveal cosmic large-scale structure at low and intermediate redshifts. If the intrinsic emission spectrum is characterized by an emission peak, cosmological tomography with gamma ray annihilation radiation is in principle possible.

The Cosmic MeV Gamma-Ray Background and Hard X-Ray Spectra of Active Galactic Nuclei: Implications for the Origin of Hot AGN Coronae

The origin of the extragalactic gamma-ray background radiation at 1-10 MeV is still unknown. Although the cosmic X-ray background (CXB) up to a few hundreds keV can be accounted for by the sum of Active Galactic Nuclei (AGNs), current models of AGN spectra cannot explain the background spectrum beyond ~1 MeV, because of the thermal exponential cutoff of electron energy distribution assumed in the models. Here we construct a new spectral model by calculating the Comptonization process including nonthermal electrons, which are expected to exist in an AGN hot corona if it is heated by magnetic reconnections. We show that the MeV background spectrum can nicely be explained by our model, when coronal electrons have a nonthermal power-law component whose total energy is a few percent of the thermal component and whose spectral index is d(ln N_e)/d(ln E_e) ~ -4. Although the MeV gamma-ray flux from such a component in nearby AGN spectra is below the detection limit of past observations, it could be detected by planned future MeV detectors. We point out that the amount of the nonthermal component and its electron index are similar to those found for electrons accelerated by magnetic reconnections in solar flares and the Earth magnetosphere, giving a support to the reconnection hypothesis for the origin of hot AGN coronae.

Cosmic ray origin of the diffuse gamma-ray background radiation

As a test of our unified theory of cosmic rays and high energy astrophysical phenomena, we have calculated the diffuse gamma ray background radiation produced by inverse Compton scattering of cosmic-microwave-background and starlight photons by Galactic and extragalactic cosmic ray electrons. The main sources of such electrons are the highly relativistic jets from supernova explosions and active galactic nuclei. We show that our calculations well reproduce the spectrum and intensity of the diffuse gamma-ray background radiation measured by EGRET in directions away from the Galactic disk and centre.

Gamma ray background radiation for glass electrode RPCs in the CMS/LHC environment, estimation approach with GEANT4 Monte Carlo simulation packages

Resistive plate chambers (RPCs) are gaseous parallel-plate detectors with good spatial and time resolution, which makes them very useful in high energy physics and astrophysics experiments. In the present study, glass plates are utilized as the electrodes in the construction of RPCs, these kinds of glass-RPCs are being used in many ongoing high energy physics experiments. In this paper, for the first time Monte Carlo simulation of 2 mm gas gap RPCs with glass electrodes have been performed with GEANT4 standard and low-energy packages. Gamma ray propagation through these RPCs with two types of sources, is discussed. We report measurements of the response of a glass RPC for gamma rays of energy in the range 0.1–1000.0 MeV. As expected glass electrode RPCs give higher sensitivity results than bakelite plates RPCs. The obtained results show a good agreement between GEANT4 standard and low-energy packages (showing ∼99% agreement for both low and high energy gamma rays). The evaluated results are applied to both endcap and barrel areas of CMS regions. According to these results, a hit rate of about 100, 50 and 30 Hz cm−2 is calculated using GEANT4 standard electromagnetic package for a 20×20 cm2 glass RPC in the ME1, ME2, and ME4 regions respectively. While for the same gamma source and GEANT4 package, a hit rate of about 0.46 and 1.40 Hz cm−2 was computed for the MB1 and MB4 stations respectively. Similar characteristics of hit rates have been observed for the GEANT4 low electromagnetic package.