Ray Emission Research Articles

Contribution from Ultrahigh-Energy Cosmic Rays to the Extragalactic Diffuse Gamma Ray Emission

The diffuse gamma ray emission produced by ultrahigh-energy cosmic rays (E > 4 × 1019 eV) in intergalactic space is discussed. Particles with monoenergetic or hard injection spectra, formed probably upon the acceleration of particles in supermassive black holes, are considered. It is found that intensity of the diffuse gamma ray emission depends on the shape of the injection spectrum. It is therefore concluded that data on intergalactic gamma ray emission can be used to investigate supermassive black holes.

Massive star clusters as the an alternative source population of galactic cosmic rays

Extended gamma -ray emissions in the vicinity of young star clusters are believed to be produced by the interaction of CRs accelerated therein with the ambient gas. The detailed spatial analysis reveals 1/r type distribution of CRs, which indicates a continuous injection of CRs in these objects. The hard, propto E^{-2.3} type power-law energy spectra of parent protons continue up to sim 1 PeV. The efficiency of conversion of kinetic energy of powerful stellar winds to CRs can be as high as 10%. This implies that the young massive stars can operate as effective proton PeVatrons with a major or even dominant contribution to the flux of highest-energy galactic CRs.

Monte Carlo calculation of the average neutron depolarization for the NPDGamma experiment

The NPDGamma experiment measures the asymmetry in $\gamma$-ray emission in the capture of polarized neutrons on liquid parahydrogen. The beam polarization is measured using $^3$He spin analysis, but this measurement does not account for the contribution of depolarization from spin-flip scattering primarily due to orthohydrogen in the bulk liquid. This is a systematic effect that dilutes the experimental asymmetry and is modeled using Monte Carlo. Methods for tracking neutron spin in MCNPX were developed in order to calculate the average neutron polarization upon capture for use as a multiplicative correction to the measured beam polarization for the NPDGamma experiment.

Search for γ -ray emission from dark matter particle interactions from the Andromeda and Triangulum galaxies with the Fermi Large Area Telescope

The Andromeda (M31) and Triangulum (M33) galaxies are the closest Local Group galaxies to the Milky Way, being only 785 and 870 kpc away. These two galaxies provide an independent view of high-energy processes that are often obscured in our own Galaxy, including possible signals of dark matter (DM) particle interactions. The Fermi Large Area Telescope (Fermi-LAT) preliminary eight year list of sources includes both M31, which is detected as extended with a size of about 0.4$^\circ$, and M33, which is detected as a point-like source. The spatial morphology of M31 $\gamma$-ray emission could trace a population of unresolved sources and energetic particles originating in sources not related to massive star formation. Alternatively, the $\gamma$-ray emission could also be an indication of annihilation or decay of DM particles. We investigate these two possibilities using almost 10 years of data from the Fermi LAT. An interpretation that involves only a DM $\gamma$-ray emission is in tension with the current limits from other searches, such as those targeting Milky Way dwarf spheroidal galaxies. When we include a template of astrophysical emission, tuned on $\gamma$-ray data or from observations of these galaxies in other wavelengths, we do not find any significant evidence for a DM contribution and we set limits for the annihilation cross section that probe the thermal cross section for DM masses up to a few tens of GeV in the $b\bar{b}$ and $\tau^+\tau^-$ channels. For models where the DM substructures have masses above $10^{-6}$ solar masses our limits probe the DM interpretation of the Fermi LAT Galactic center excess. We provide also the lower limit for the DM decay time assuming the same spatial models of the DM distribution in M31 and M33.

RAY-BASED SEGMENTATION ALGORITHM FOR MEDICAL IMAGING

Abstract. In this study, we present a segmentation algorithm based on ray casting and border point detection. The algorithm’s main parameter is the number of emitted rays, which defines the resolution of the object’s boundary. The value of this parameter depends on the shape of the target region. For instance, 8 rays are enough to segment the left ventricle with the average Dice similarity coefficient approximately equal to 85%. Having gathered the data of rays, the training datasets had a relatively high level of class imbalance (up to 90%). To cope with this issue, ensemble-based classifiers used to manage imbalanced datasets such as AdaBoost.M2, RUSBoost, UnderBagging, SMOTEBagging, SMOTEBoost were used for border detection. For estimation of the accuracy and processing time, the proposed algorithm used a cardiac MRI dataset of the University of York and brain tumour dataset of Southern Medical University. The highest Dice similarity coefficients for the heart and brain tumour segmentation, equal to 86.5 ± 6.9% and 89.5 ± 6.7%, respectively, were achieved by the proposed algorithm. The segmentation time of a cardiac frame equals 4.1 ± 2.3 ms and 20.2 ± 23.6 ms for 8 and 64 rays, respectively. Brain tumour segmentation took 5.1 ± 1.1 ms and 16.0 ± 3.0 ms for 8 and 64 rays respectively. By testing the different medical imaging cases, the proposed algorithm is not time-consuming and highly accurate for convex and closed objects. The scalability of the algorithm allows implementing different border detection techniques working in parallel.

Characterization of prompt gamma ray emission for in vivo range verification in particle therapy: A simulation study

In this paper we investigate the emission and detection characteristics of prompt gamma (PG) rays for in vivo range verification during hadron therapy, using Geant4 simulations. Proton, 4He and 12C beams of varying energy are incident on water phantoms. The PG production yield, energy spectral characteristics and spatial correlation with the Bragg Peak (BP) have been quantified. Further, the angular distributions for PG detection with respect to a point-of-reference on the phantom surface have been explored. The temporal properties of PG emission and time-of-flight (TOF) of PG detection have also been investigated in correlation with the changing particle beam range. Our results show that the primary PG rays from nuclear interactions of the primary beam exhibit the closest correlation to the beam range but its signal is significantly masked by the concurrent secondary PG rays, particularly for heavier ions such as carbon ion beams. The PG TOF spectroscopy encodes the essential information of the beam range but requires high time resolution measurements to retrieve it. A hybrid PG detection system to utilize the energy, timing and spatial characteristics of PG rays is desirable for BP tracking in real-time.

Search for multiwavelength emission from the binary millisecond pulsar PSR J1836-2354A in the globular cluster M22

We present a multi-band search for X-ray, optical and $\gamma$-ray emission of the radio binary millisecond pulsar J1836-2354A, hosted in the globular cluster M22. X-ray emission is significantly detected in two Chandra observations, performed in 2005 and 2014, at a luminosity of $\sim$2-3$\times$10$^{30}$ erg s$^{-1}$, in the 0.5-8 keV energy range. The radio and the X-ray source positions are found consistent within 1$\sigma$ error box. No detection is found in archival XMM-Newton and Swift/XRT observations, compatible with the Chandra flux level. The low statistics prevents us to assess if the X-ray source varied between the two observations. The X-ray spectrum is consistent with a power-law of photon index $\sim$1.5. We favour as the most probable origin of the X-ray emission an intrabinary shock scenario. We searched for optical and $\gamma$-ray counterparts to the radio source using data from Hubble Space Telescope and Fermi-LAT catalogues, respectively. No optical counterpart down to V=25.9 and I=24.7 (3$\sigma$) is detected, which suggests a companion mass of 0.1-0.2 $M_\odot$. Combined with the low X-ray luminosity, this is consistent with a black widow nature of PSR J1636-2354A. Inspecting the 8-year Fermi-LAT catalogue, we found a $\gamma$-ray source, 4FGL J1836.8-2354, with a positional uncertainty consistent with the globular cluster, but not with the radio position of the millisecond pulsar.

Radiative control through greenhouse covering materials using pigmented coatings

Greenhouses are built in hot climates to provide a cool environment suitable for growing out of season crops. Their temperature is usually controlled by utilizing air conditioning systems and shading the transparent cover material in peak sun hours. A new method to keep a cool greenhouse, and reduce energy consumption is proposed in this study. Using a new approach for pigmented coatings, that would reflect incident solar radiation in the infrared wavelengths (NIR), and allows the shorter visible wavelengths (VIS) to be transmitted. It is possible to reduce the heat gain inside the green house by radiation while keeping the useful wavelengths necessary for photosynthesis. A series of numerical calculations is performed, modeling the radiation transfer in the pigmented coating using the Radiation Element Method by Ray Emission Model (REM2). Mono dispersed particles are assumed, and Mie theory is used to estimate the radiative scattering properties of the particles. Different materials are studied as pigments and compared over a range of particle sizes and volume fractions. The calculated spectral reflectance curves were compared with experimentally derived ones of TiO2 pigmented coating, they differed in values but showed the same tendency. An optimization parameter is proposed and used to compare the different materials and parameters. Diamond particles are found to be the most appropriate candidate for the desired application, giving a high transmittance in the VIS region and high reflectance in the NIR region.

Optimization of Am–Be millicuries neutron source in a small volume cylindrical water tank for NAA

The neutron activation analysis (NAA) is a very powerful method for multi-element analysis of samples. NAA technique needs to be developed for low neutron flux in millicuries using the 241Am-Be neutron source. To optimize sample and neutron source geometry for maximum γ-ray yield for neutron activation analysis. Gamma ray neutron activation analysis (NAA) has been set up where a 50-millicurie Am-Be neutron source is available. In this experimental setup, the neutron source is placed at the center of a cylindrical water tank of 40 x 40 cm in xyz plan, and thermal neutrons are produced at a distance of 1.2 cm from the source. The system is used for the activation analysis of sodium carbonate, sodium chloride and copper with the gamma ray emissions of 1.37, 1.73, 2.25 and 2.76 MeV for 24Na and 0.511 MeV for 64Cu having half lives of 15 hrs and 12.9 hrs, respectively. The thermal neutron activation analysis has been demonstrated by placing the samples at about 1.2 cm from the neutron source. HPGe and 3x3 inch NaI(Tl) gamma ray spectrometers have been used for the gamma ray spectrometry of these activated samples with the use of a Marinelli beaker. The geometry of the sample with respect to the neutron source has been optimized for the maximum γ-ray yield in NAA. The geometry of the sample with respect to the neutron source has been optimized for the maximum γ-ray yield in NAA. The increase in gamma ray flux distribution in the medium of water, due to the neutron source inside the tank, has been observed by a GM detector which is due to the production of short-lived 16N on activation of 16O in water. This system can also be used for prompt γ-ray analysis.

The rare extended radio-loud narrow-line Seyfert 1 galaxy SDSS J1030+5516 at high resolution

Recently, Rakshit et al. (Astrophys. J. 869:173, 2018) reported the discovery of SDSS J103024.95+ 551622.7, a radio-loud narrow-line Seyfert 1 galaxy having a {sim}100 kpc scale double-lobed radio structure. Here we analyse archival radio interferometric imaging data taken with the Very Large Array (VLA) at 5 GHz, and with the Very Long Baseline Array (VLBA) at 4.3 and 7.6 GHz. Two hotspots and a compact core are detected with the VLA at arcsec scale, while a single milliarcsec-scale compact radio core is seen with the highest resolution VLBA observations. The Fermi Large Area Telescope did not detect gamma -ray emission at the position of this source. In the mid-infrared, the Wide-field Infrared Survey Explorer satellite light curve, covering more than 7 years and including the most recent data points, hints on flux density variability at 3.4 μm. Our findings support the notion that this source is a young version of Fanaroff–Riley type II radio galaxies.

Correlations between the shifts in prompt gamma emission profiles and the changes in daily target coverage during simulated pencil beam scanning proton therapy

The aim of this study was to investigate the feasibility of using prompt gamma (PG) ray emission profiles to monitor changes in dose to the planning target volume (PTV) during pencil beam scanning (PBS) proton therapy as a result of day-to-day variation in patient anatomy.For 11 prostate patients, we simulated treatment plan delivery using the patients’ daily anatomy as observed in the planning CT and 7–9 control CT scans, including the detected PG profiles resulting from the 5%, 10%, and 20% most intense proton pencil beams. For each patient, we determined the changes in dosimetric parameters for the high- and low-dose PTVs between the simulations performed using the planning CT scan and the different control CT scans and correlated these to changes in the PG emission profiles.Changes in coverage of the high- and low-dose PTV correlated most strongly with the median and mean absolute PG emission profile shifts of the 5% most intense pencil beams, respectively. With a mean Pearson correlation coefficient of −0.76 (SD: 0.17) for the high-dose PTV and of −0.60 (SD: 0.51) for the low-dose PTV.We showed, as a proof of principle, that PG emission profiles obtained during PBS proton therapy could be used to detect changes in PTV coverage due to day-to-day anatomical variation.

Development of a simulation code for material analysis using the PIGE technique

Particle Induced Gamma ray Emission (PIGE) is a well known and widely used Ion Beam Analysis (IBA) technique for non-destructive material analysis, usually in conjunction with Proton Induced X-ray Emission (PIXE). The main drawback in the applicability of PIGE regarding the quantification of light elements in various heavy element substrates is the need for many reference targets with similar matrices to the one under study, because of the importance of the ion energy loss in the calculations. In order to overcome this problem, an appropriate simulation code that uses as inputs the experimental spectrum and the relevant differential cross sections, with the output being the quantification of the concentration depth profiles of the isotopes of interest is needed. A code like this is currently being developed in C++ and it is compatible with Windows, Linux and Mac.

Ammonium Hydroxide Mediated Hydrothermal Crystallization of Hydroxyapatite Coatings on Titanium Substrate

Controlled growth of hydroxyapatite (HAp) coatings on titanium substrate plays an important role in the fabrication of the composites for bone tissue engineering. We describe the synthesis of the crystalline hydroxyapatite coatings on the Ti/TiO2 substrate through a hydrothermal method by using ethylenediamine tetraacetic acid disodium salt (Na2EDTA) and varying concentrations of ammonium hydroxide (NH4OH) in calcium-phosphate precursor solution. Na2EDTA serves as a chelating agent, while NH4OH is used as an alkaline source and crystal growth modifier. We characterized the HAp coatings using x-ray diffraction, scanning electron microscopy, and Raman spectroscopy. We also performed the elemental chemical analysis by means of a particle induced x–ray emission method. Our results show that there is a pH limit for which the hydrothermal deposition of HAp on titanium occurs. Moreover, we observed that NH4OH had a measurable influence on the coating thickness as well as on the size and shape of the HAp crystals. We found that with the increase of NH4OH concentration, the thickness of the Hap layer increases and its morphology changes from irregular flakes to well-defined hexagonal rods.

Radio forensics could unmask nearby off-axis gamma-ray bursts

The multi-messenger observation of gamma-ray burst (GRB)\,170817A from the nearby binary neutron-star merger GW170817 demonstrated that low-energy $\gamma$-ray emission can be observed at relatively large angles from GRB jet axes. If such structured emission is typical, then the currently known sample of short GRBs with no distance measurements may contain multiple nearby off-axis events whose delayed afterglows could have gone undetected. These nearby neutron star mergers may produce telltale radio flares peaking years after the prompt GRB emission that could still be observable. Here, we show that several short GRBs observed by the Burst Alert Telescope (BAT) on the Neil Gehrels \textit{Swift} satellite, with no identified afterglow and no distance measurement, could potentially be associated with radio flares detectable by sensitive cm-wavelength radio facilities such as the Karl G. Jansky Very Large Array. We also examine optical follow-up observations that have been carried out for these events, and find that a nearby GW170817-like kilonova is ruled out for only a third of them.

Gamma-ray emission of hot astrophysical plasma

Very hot plasmas with ion temperature exceeding $10^{10}$ K can be formed in certain astrophysical environments. The distinct radiation signature of such plasmas is the $\gamma$-ray emission dominated by the prompt de-excitation nuclear lines and $\pi^0$-decay $\gamma$-rays. Using a large nuclear reaction network, we compute the time evolution of the chemical composition of such hot plasmas and their $\gamma$-ray line emissivity. At higher energies, we provide simple but accurate analytical presentations for the $\pi^0$-meson production rate and the corresponding $\pi^0\to2\gamma$ emissivity derived for the Maxwellian distribution of protons. We discuss the impact of the possible deviation of the high energy tail of the particle distribution function from the "nominal" Maxwellian distribution on the plasma $\gamma$-ray emissivity.

Nuclear γ-ray emission from very hot accretion flows

Optically thin accretion plasmas can reach ion temperatures Ti ≥ 1010 K and thus trigger nuclear reactions. Using a large nuclear interactions network, we studied the radial evolution of the chemical composition of the accretion flow toward the black hole and computed the emissivity in nuclear γ-ray lines. In the advection dominated accretion flow (ADAF) regime, CNO and heavier nuclei are destroyed before reaching the last stable orbit. The overall luminosity in the de-excitation lines for a solar composition of plasma can be as high as few times 10−5 the accretion luminosity (Ṁc2) and can be increased for heavier compositions up to 10−3. The efficiency of transformation of the kinetic energy of the outflow into high energy (≥100 MeV) γ-rays through the production and decay of π0-mesons can be higher, up to 10−2 of the accretion luminosity. We show that in the ADAF model up to 15% of the mass of accretion matter can “evaporate” in the form of neutrons.

Key Ne19 States Identified Affecting γ -Ray Emission from F18 in Novae

Detection of nuclear-decay $\gamma$ rays provides a sensitive thermometer of nova nucleosynthesis. The most intense $\gamma$-ray flux is thought to be annihilation radiation from the $\beta^+$ decay of $^{18}$F, which is destroyed prior to decay by the $^{18}$F($p$,$\alpha$)$^{15}$O reaction. Estimates of $^{18}$F production had been uncertain, however, because key near-threshold levels in the compound nucleus, $^{19}$Ne, had yet to be identified. This Letter reports the first measurement of the $^{19}$F($^{3}$He,$t\gamma$)$^{19}$Ne reaction, in which the placement of two long-sought 3/2$^+$ levels is suggested via triton-$\gamma$-$\gamma$ coincidences. The precise determination of their resonance energies reduces the upper limit of the rate by a factor of $1.5-17$ at nova temperatures and reduces the average uncertainty on the nova detection probability by a factor of 2.1.

Measurement of redshift-dependent cross-correlation of HSC clusters andFermiγ-rays

The cross-correlation study of the unresolved $\gamma$-ray background (UGRB) with galaxy clusters has a potential to reveal the nature of the UGRB. In this paper, we perform a cross-correlation analysis between $\gamma$-ray data by the Fermi Large Area Telescope (Fermi-LAT) and a galaxy cluster catalogue from the Subaru Hyper Suprime-Cam (HSC) survey. The Subaru HSC cluster catalogue provides a wide and homogeneous large-scale structure distribution out to the high redshift at $z=1.1$, which has not been accessible in previous cross-correlation studies. We conduct the cross-correlation analysis not only for clusters in the all redshift range ($0.1 < z < 1.1$) of the survey, but also for subsamples of clusters divided into redshift bins, the low redshift bin ($0.1 < z < 0.6$) and the high redshift bin ($0.6 < z < 1.1$), to utilize the wide redshift coverage of the cluster catalogue. We find the evidence of the cross-correlation signals with the significance of 2.0-2.3$\sigma$ for all redshift and low-redshift cluster samples. On the other hand, for high-redshift clusters, we find the signal with weaker significance level (1.6-1.9$\sigma$). We also compare the observed cross-correlation functions with predictions of a theoretical model in which the UGRB originates from $\gamma$-ray emitters such as blazars, star-forming galaxies and radio galaxies. We find that the detected signal is consistent with the model prediction.

Onset Time of the GLE 72 Observed at Neutron Monitors and its Relation to Electromagnetic Emissions

We present an overview of the ground-level enhancement (GLE 72) of the cosmic-ray intensity associated with the recent powerful solar flare SOL2017-09-10 (X-ray class X8.9) based on the available neutron monitor (NM) network observations and on data from the satellite GOES 13. The maximum increase at high-latitude near-sea-level NMs was ${\approx }\,6\,\mbox{--}\,7\%$ (2-min averages), greater with better time resolution. A scatter plot of the maximum increase of the GLE versus solar energetic-particle (SEP, proton) flux ${>}\,100~\mbox{MeV}$ shows one of the softest spectra among GLEs relative to the SEP fluxes. However, at two high-mountain middle-latitude NMs the increase was ${\approx }\,1\%$ , indicating the possibility of proton acceleration up to 6 GeV. Among the analyzed NM data the Fort Smith (FSMT) NM shows the earliest and the rather high increase between 16:06 – 16:08 UT. This indicates an anisotropy in the first phase of the GLE event. We calculate the acceptance cones of several NM stations at high latitudes and contours of pitch angles corresponding to the interplanetary magnetic field (IMF). When employing the available data we find that pion-decay $\gamma $ -ray emission onset is in accordance with the time of the main flare energy release. The observed time interval of the impulsive burst of ${>}\,100~\mbox{MeV}$ $\gamma $ -ray emission probably corresponds to the time of a turbulent current sheet creation. The observed location of the impulsive burst pion-decay emission source coincides with the active region and the cusp-shaped structure. It seems that models assuming sub-relativistic proton production beginning in a turbulent reconnecting current sheet are consistent with the observations. If these particles were released from the Sun during a type III emission with a pion-decay maximum at $16{:}00{:}30\pm 30~\mbox{UT}$ , we get a plausible path length equal to $1.5\pm 0.3~\mbox{AU}$ of the particles responsible for the onset of the SEP event and GLE. The time lag of GLE 72 corresponds to the most probable interval of the time difference between GLE onset and main flare energy release. Although other scenarios are not excluded we attribute the protons that create the pion-decay emission and the protons responsible for the GLE and SEP event onset to a general population of accelerated particles.

Positron flux and γ-ray emission from Geminga pulsar and pulsar wind nebula

Nearby pulsars have been suggested as sources of $\sim$TeV $e^+/e^-$ Cosmic Ray (CR) excess on Earth. The High-Altitude Water Cherenkov Observatory (HAWC) detected extended TeV emission regions in the direction of two nearby middle-aged pulsars, Geminga and PSR B0656+14. By modeling the TeV emission as inverse Compton emission from electron-positron pairs diffusing in the interstellar medium (ISM), the HAWC collaboration derives a diffusion coefficient much smaller than the standard value in the vicinity of the two pulsars, which make them unlikely the origin of the positron excess. We propose that the observed $\gamma$-ray emission originate from the relic pulsar wind nebula. A two zone diffusion model with a slow diffusion in the nebula and a fast diffusion in the ISM can explain the HAWC surface brightness profile and the positron excess simultaneously. Inefficient diffusion in the $\gamma$-ray emission region surrounding a middle-aged pulsar maybe a common phenomenon that can be tested by future observation. The implied diffusion coefficient in the ISM is smaller than the one suggested by the standard CR propagation model, but it is fully consistent with the predictions of the spiral arm model.