High Energy Gamma-ray Research Articles

Performance of the DAMPE BGO calorimeter on the ion beam test

The DArk Matter Particle Explorer (DAMPE), which is a Chinese space telescope for the precise measurement of high-energy electrons, gamma rays, and nuclei from deep space, was successfully launched on December 17, 2015. The DAMPE electromagnetic calorimeter made of bismuth germanium oxide (BGO) crystals can measure incident hadron energies from 50 GeV to 100 TeV. The calorimeter was tested with ion beams at CERN in 2015. The energy responses to ions from helium to argon are investigated. The result is reproduced by a Monte Carlo simulation based on Geant4 with two physics process models. It shows that the simulation results of a beam test are independent of the physics models adopted. Additionally, quenching effects of the BGO crystal on the ions are observed with this beam test. The quenching attenuations increase with the atomic number and were approximately 7% for boron and 40% for argon.

Neutron absorption in supermirror coatings: Effects on shielding

The quantification of the dose rate and the composition of the dose in the vicinity of supermirror coated guides is essential for designing shielding for beamlines transporting neutrons with a high flux. We present results on a calculation of radiative neutron absorption in Ni/Ti and NiMo/Ti supermirror coatings which leads to the emission of high energy gamma rays. A simple parameterization of the absorption probability in the coating materials per incident neutron is given as a function of momentum transfer at reflection.

An analog-to-digital converter and intelligent controller for use in a DAQ system processing PMT signals from very high energy astrophysics experiments

Abstract Modern instrumentation for very high energy gamma-ray astronomy and astrophysics requires efficient and precise digitization of PMT signals from Cherenkov light generated by incoming cosmic ray particles over the energy range from hundreds of GeV up to several hundred TeV. This dynamic range of more than 1000 is coupled with a requirement for very low noise operation. We have developed modern multi-channel analog-to-digital converters (model BPA-8) together with a data acquisition system, managed with an intelligent crate-controller (model K-167) which controls the measurement modules. The electronics described in this paper is accepted to be used to record PMT signals with high precision and efficiency, allowing reliable extraction and precise analysis of Cherenkov signals from high energy gamma-rays emitted by astrophysical objects.

Probing the IGMF with the Next Generation of Cherenkov Telescopes

Abstract Intergalactic space is believed to contain nonzero magnetic fields (the Intergalactic Magnetic Field: IGMF), which at scales of megaparsecs would have intensities below 10−9 G. Very high energy (VHE > 100 GeV) gamma-rays coming from blazars can produce e+e− pairs when interacting with the extragalactic background light (EBL) and the cosmic microwave background, generating an electromagnetic cascade of megaparsec scale. The IGMF may produce a detectable broadening of the emission beam that could lead to important constrains both on the IGMF intensity and its coherence length. Using the Monte Carlo–based Elmag code, we simulate the electromagnetic cascade corresponding to two detected TeV sources: PKS 2155-304 visible from the south and H1426+428 visible from the north. Assuming an EBL model and intrinsic spectral properties of the sources, we obtain the spectral and angular distribution of photons when they arrive at Earth. We include the response of the next generation Cherenkov telescopes by using simplified models for Cherenkov Telescope Array (CTA)-south and CTA-north based on a full simulation of each array performance. Combining the instrument properties with the simulated source fluxes, we calculate the telescope point-spread function for null and non-null IGMF intensities and develop a method to test the statistical feasibility of detecting IGMF imprints by comparing the resulting angular distributions. Our results show that for the analyzed source PKS 2155-304 corresponding to the southern site, CTA should be able to detect IGMF with intensities stronger than 10−14.5 G within an observation time of ∼100 hr.

The search for X-ray emission from electron/positron pair halos using the XMM-Newton observatory

An electron/positron pair halo is formed by electromagnetic cascades that initiate when high energy gamma-rays from extragalactic sources - i.e. Blazar AGN - interact with the cosmic infrared background (CIB), and are then absorbed via the electron/positron pair production process. The high energy electron/positron pairs produced could up-scatter the cosmic microwave background (CMB) and become gamma rays which can interact with CIB again. Thus, the process could happen continuously until the produced gamma-rays have insufficient energy to interact with the CIB. Indeed, given the presence of intergalactic magnetic field, the produced electron/positron pairs could gyrate before scattered with the CMB photons so that they emit X-ray photons via the synchrotron radiation process. In this work, we determine whether the predicted X-ray photons emitted from the halo can be detected by the current generation X-ray observatory: XMM-Newton. The Spectral Energy Distributions (SEDs) of the synchrotron radiation of the pair halo predicted to be obtained from the AGN H1426+428 are simulated by the Monte Carlo simulations method; these are used as a source model for simulating observed spectra. The spectra of the halo virtually observed by XMM-Newton are generated in three different regions: the inner region, outer region and the region out of the XMM-Newton’s field of view. The resulting spectra suggest that the outer region spectra could provide the best opportunity to detect and confirm the existence of electron/positron pair halos.

Extreme HBL behavior of Markarian 501 during 2012

Aims. We aim to characterize the multiwavelength emission from Markarian 501 (Mrk 501), quantify the energy-dependent variability, study the potential multiband correlations, and describe the temporal evolution of the broadband emission within leptonic theoretical scenarios. Methods. We organized a multiwavelength campaign to take place between March and July of 2012. Excellent temporal coverage was obtained with more than 25 instruments, including the MAGIC, FACT and VERITAS Cherenkov telescopes, the instruments on board the Swift and Fermi spacecraft, and the telescopes operated by the GASP-WEBT collaboration. Results. Mrk 501 showed a very high energy (VHE) gamma-ray flux above 0.2 TeV of ∼0.5 times the Crab Nebula flux (CU) for most of the campaign. The highest activity occurred on 2012 June 9, when the VHE flux was ∼3 CU, and the peak of the high-energy spectral component was found to be at ∼2 TeV. Both the X-ray and VHE gamma-ray spectral slopes were measured to be extremely hard, with spectral indices < 2 during most of the observing campaign, regardless of the X-ray and VHE flux. This study reports the hardest Mrk 501 VHE spectra measured to date. The fractional variability was found to increase with energy, with the highest variability occurring at VHE. Using the complete data set, we found correlation between the X-ray and VHE bands; however, if the June 9 flare is excluded, the correlation disappears (significance < 3σ) despite the existence of substantial variability in the X-ray and VHE bands throughout the campaign. Conclusions. The unprecedentedly hard X-ray and VHE spectra measured imply that their low- and high-energy components peaked above 5 keV and 0.5 TeV, respectively, during a large fraction of the observing campaign, and hence that Mrk 501 behaved like an extreme high-frequency-peaked blazar (EHBL) throughout the 2012 observing season. This suggests that being an EHBL may not be a permanent characteristic of a blazar, but rather a state which may change over time. The data set acquired shows that the broadband spectral energy distribution (SED) of Mrk 501, and its transient evolution, is very complex, requiring, within the framework of synchrotron self-Compton (SSC) models, various emission regions for a satisfactory description. Nevertheless the one-zone SSC scenario can successfully describe the segments of the SED where most energy is emitted, with a significant correlation between the electron energy density and the VHE gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. The one-zone SSC scenario used reproduces the behavior seen between the measured X-ray and VHE gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the X-rays.

Long-term optical monitoring of TeV emitting blazars

We present ten years of R-band monitoring data of 31 northern blazars which were either detected at very high-energy (VHE) gamma rays or listed as potential VHE gamma-ray emitters. The data comprise 11 820 photometric data points in the R-band obtained in 2002–2012. We analyzed the light curves by determining their power spectral density (PSD) slopes assuming a power-law dependence with a single slope β and a Gaussian probability density function (PDF). We used the multiple fragments variance function (MFVF) combined with a forward-casting approach and likelihood analysis to determine the slopes and perform extensive simulations to estimate the uncertainties of the derived slopes. We also looked for periodic variations via Fourier analysis and quantified the false alarm probability through a large number of simulations. Comparing the obtained PSD slopes to values in the literature, we find the slopes in the radio band to be steeper than those in the optical and gamma rays. Our periodicity search yielded one target, Mrk 421, with a significant (p < 5%) period. Finding one significant period among 31 targets is consistent with the expected false alarm rate, but the period found in Mrk 421 is very strong and deserves further consideration.

Review and Performance Comparison of Lead-Free Shields and Lead Shields, In Terms of Biological Effects in Nuclear Medicine by the Comet Method

Introduction: Ionizing radiation can cause damage to biologically important DNA molecules. Radiation in nuclear medicine radiation exposes people working in from two main positions; administer in gradiopharmaceuticals (the barn and squeezing a generator, procurement, distribution and drug infusion) and patients that receive radiation treatment (patients that are prescribed a radiopharmaceutical). Use of lead aprons is disputed practice in radiation treatment due to the creation of special lead X-rays of high-energy gamma ray collisions and the high absorption coefficient of such radiations in the body. Correct use of personal protective equipment, such as uniforms and flexible protection, and compliance with radiation protection can greatly reduce damage. Flexible lead shields are usually made from materials such as rubber; polymers or elastomers (polymers that are elastic) are used as the basis for fine lead particles. The problems with lead shields have led to recent discussion of the use of lead-free shields. If the biological effects caused by lead-free shields give less than two states with and without a lead shield, the shield that is lighter, weaker and that doesn’t cause environmental pollution, can be used in place of lead. Materials and Methods: To review and achieve the above objective, blood samples were taken from non-radiation operatives and poured in heparin tubes, and then placed in the considered distance of time and place; after radiation, they were exposed to gamma radiation resulting from technetium, comet assay will be performed on them. Results: density was super less dense compared to the lead and was about one-tenth of the density of lead (1.23). DNA damage in both groups (with and without a lead shield) is greater when compared with the control group. Conclusion: By using two-way analysis of variance, the time variable was significantly effective in increasing the damage. In addition, the type of shield variable (lead or lead-free) and meaningful distance have not shown.

Extending the observation limits of Imaging Air Cherenkov Telescopes toward horizon

Usually the Imaging Atmospheric Cherenkov Telescopes, used for the ground-based gamma-ray astronomy in the very high energy range 50 GeV - 50 TeV, perform air shower observations till the zenith angle of ~60 deg. Beyond that limit the column density of air increases rapidly and the Cherenkov light absorption starts playing a major role. Absence of a proper calibration method of light transmission restrained researchers performing regular measurements under zenith angles >>60 deg. We extend the observation of air showers in Cherenkov light till almost the horizon. We use an aperture photometry technique for calibrating the Cherenkov light transmission in atmosphere during observations under very large zenith angles. Along with longer in time observations of a given source, this observation technique allows one to strongly increase the collection area and the event statistics of Cherenkov telescopes for the very high energy part of the spectrum. Study of the spectra of the highest energy gamma rays from a handful of candidate sources can provide a clue for the origin of the galactic cosmic rays. We show that MAGIC very large zenith angle observations yield a collection area in excess of a square kilometer. For selected sources this is becoming comparable with the target collection area anticipated with the Cherenkov Telescope Array.

Characterization of FBK NUV-HD SiPMs for the pSCT camera proposed for the Cherenkov Telescope Array

Abstract Recent developments on Silicon Photomultipliers (SiPMs) have shown that they are particularly adequate to detect fast signal due to low-intensity light. Fondazione Bruno Kessler (FBK) has optimized these sensors for the Near-Ultraviolet Cherenkov light emitted by high energy gamma-ray showers in the atmosphere. The FBK high density SiPMs (NUV-HD) have been extensively characterized in the laboratories of the Italian Institute of Nuclear Physics (INFN) in view of equipping the focal plane camera of the Schwarzschild–Couder Telescope prototype (pSCT) in the framework of the Cherenkov Telescope Array (CTA). Here we report the performances of the 6 × 6 mm 2 SiPMs based on 40 × 40 μm 2 cells, in terms of gain and signal-to-noise ratio. We compare the results obtained on devices from the latest generation and grown on different substrates in order to choose the most suitable sensor for the pSCT camera.

Refining the origins of the gamma-ray binary 1FGL J1018.6–5856

Context. Gamma-ray binaries are systems composed of a massive star and a compact object that exhibit emission from radio to very high energy gamma rays. They are ideal laboratories to study particle acceleration and a variety of physical processes that vary as a function of the orbital phase. Aims. We aim to study the radio emission of the gamma-ray binary 1FGL J1018.6–5856 to constrain the emitting region and determine the peculiar motion of the system within the Galaxy to clarify its origin. Methods. We analyzed an observation of 1FGL J1018.6–5856 with the Australian Long Baseline Array (LBA) at 8.4 GHz to obtain an accurate astrometry of the system and study its emission on milliarcsecond scales. We combined these data with the optical Gaia DR2 and UCAC4 catalogs to consolidate the astrometry information therein. Results. The gamma-ray binary 1FGL J1018.6–5856 shows compact radio emission (< 3 mas or ≲20 au at ∼6.4 kpc distance), implying a brightness temperature of ≳5.6 × 106 K, and confirming its nonthermal origin. We report consistent results between the proper motion reported by Gaia DR2 and the positions obtained from the Gaia DR2, UCAC4, and LBA data (spanning 20 yr in total). We also determined the distance to 1FGL J1018.6–5856 to be 6.4−0.7+1.7. Together with the radial velocity of the source we computed its three-dimensional (3D) proper and peculiar motion within the Galaxy. We obtained a peculiar motion of 1FGL J1018.6–5856 on its regional standard of rest (RSR) frame of |u| = 45−9+30, with the system moving away from the Galactic plane. In the simplest scenario of a symmetric stellar core collapse we estimate a mass loss of 4 ≲ ΔM ≲ 9 M⊙ during the creation of the compact object. Conclusions. 1FGL J1018.6–5856 exhibits compact radio emission similar to that detected in other gamma-ray binaries. We provide the first accurate peculiar motion estimations of the system and place it within the Galaxy. The obtained motion and distance excludes the physical relation of the binary source with the supernova remnant (SNR) G284.3−1.8.

Nonthermal emission from high-mass microquasar jets affected by orbital motion

Context. The stellar wind in high-mass microquasars should interact with the jet. This interaction, coupled with orbital motion, is expected to make the jet follow a helical, nonballistic trajectory. The jet energy dissipated by this interaction, through shocks for example, could lead to nonthermal activity on scales significantly larger than the system size.Aims. We calculate the broadband emission from a jet affected by the impact of the stellar wind and orbital motion in a high-mass microquasar.Methods. We employ a prescription for the helical trajectory of a jet in a system with a circular orbit. Subsequently, assuming electron acceleration at the onset of the helical jet region, we compute the spatial and energy distribution of these electrons, and their synchrotron and inverse Compton emission including gamma-ray absorption effects.Results. For typical source parameters, significant radio, X- and gamma-ray luminosities are predicted. The scales on which the emission is produced may reduce, but not erase, orbital variability of the inverse Compton emission. The wind and orbital effects on the radio emission morphology could be studied using very long baseline interferometric techniques.Conclusions. We predict significant broadband emission, modulated by orbital motion, from a helical jet in a high-mass microquasar. This emission may be hard to disentangle from radiation of the binary itself, although the light curve features, extended radio emission, and a moderate opacity to very high-energy gamma rays, could help to identify the contribution from an extended (helical) jet region.

Lorentz Invariance Violation Effects on Gamma–Gamma Absorption and Compton Scattering

Abstract In this paper, we consider the impact of the Lorentz invariance violation (LIV) on the γ − γ opacity of the universe to very high energy (VHE) gamma-rays, compared to the effect of local underdensities (voids) of the extragalactic background light, and on the Compton scattering process. Both subluminal and superluminal modifications of the photon dispersion relation are considered. In the subluminal case, LIV effects may result in a significant reduction of the γ − γ opacity for photons with energies ≳10 TeV. However, the effect is not expected to be sufficient to explain the apparent spectral hardening of several observed VHE γ-ray sources in the energy range from 100 GeV to a few TeV, even when including effects of plausible inhomogeneities in the cosmic structure. Superluminal modifications of the photon dispersion relation lead to a further enhancement of the EBL γγ opacity. We consider, for the first time, the influence of LIV on the Compton scattering process. We find that this effect becomes relevant only for photons at ultra-high energies, E ≳ 1 PeV. In the case of a superluminal modification of the photon dispersion relation, both the kinematic recoil effect and the Klein–Nishina suppression of the cross section are reduced. However, we argue that the effect is unlikely to be of astrophysical significance.

Fermi-LAT Observations of the 2017 September 10 Solar Flare

Abstract The Fermi-Large Area Telescope detection of the X8.2 GOES class solar flare of 2017 September 10 provides for the first time observations of a long-duration high-energy gamma-ray flare associated with a ground-level enhancement (GLE). The >100 MeV emission from this flare lasted for more than 12 hr covering both the impulsive and extended phases. We present the localization of the gamma-ray emission and find that it is consistent with the active region from which the flare occurred over a period lasting more than 6 hr. The temporal variation of the gamma-ray flux and of the proton index inferred from the gamma-ray data seems to suggest three phases in acceleration of the proton population. Based on timing arguments we interpret the last phase to be tied to the acceleration mechanism powering the powering the production of the GLE particles.

Tabletop laser-driven gamma-ray source with nanostructured double-layer target

Laser-driven gamma-ray source potentially offers a compact, cost-effective, ultra-short, and ultra-bright alternative to conventional gamma-ray sources based on large-scale particle accelerators. Based on the laser-driven approach, we use multidimensional particle-in-cell simulations to demonstrate that a nanostructured double-layer target, which consists of a nanostructured foam coated on top of a metal substrate, can absorb laser energy into high-energy electrons in the nanostructured foam, and then efficiently convert it into copious gamma photons via the nonlinear Compton scattering process enabled by the solid-density substrate, which acts as a plasma mirror to reflect the laser pulse. The effects of different nanostructures in the foam target and the oblique laser incidence are presented. It is shown that the conversion efficiency of gamma photons increases when the size of nanoparticles decreases or the filling factor of nanoparticles increases in nanostructured foam target, but decreases when the laser incidence angle increases. At realistic conditions with nanostructured foam and non-normal incidence, the double-layer target still exhibits an unprecedentedly high conversion efficiency in high-energy gamma-ray production due to the laser reflection by the plasma mirror, which can be two and even three orders of magnitude higher than that of the single-layer target without the substrate using currently available lasers with intensity of 1021 .

Polynomial Data Compression for Large-Scale Physics Experiments

The next generation of research experiments will introduce a huge data surge to continuously increasing data production by current experiments. This data surge necessitates efficient compression techniques. These compression techniques must guarantee an optimum trade-off between compression rate and the corresponding ratio of compression to decompression speed without affecting the data integrity. This work presents a lossless compression algorithm to compress physics data generated by astronomy, astrophysics and particle physics experiments. The developed algorithms have been tuned and tested on a real-use case: the next-generation, ground-based, high-energy gamma ray observatory, Cherenkov Telescope Array, requiring important compression performance. As a stand-alone method, the proposed compression method is very fast and reasonably efficient. Alternatively, applied as a pre-compression algorithm, it can accelerate common methods like the Lempel–Ziv–Markov chain algorithm (LZMA), keeping close performance.

Two Blobs in a Jet Model for the γ-Ray Emission in Radio Galaxies

Abstract In the unified scheme, FR I type radio galaxies are identified with the blazar type active galaxies for which jets are aligned at large angles to the line of sight. A few radio galaxies of this type have been discovered to emit GeV–TeV gamma-rays. We consider a scenario that naturally explains the very high energy gamma-ray emission at large angles to the jet axis. It is proposed that two emission regions are present in the jet at this same moment. The inner region (blob I) moves with the large Lorentz factor, producing radiation strongly collimated along the jet axis, as observed in BL Lac type blazars. On the other hand, the outer region (blob II), which moves with the mild Lorentz factor, contains isotropically distributed relativistic electrons in the blob reference frame. These electrons upscatter monodirectional soft radiation from blob I preferentially in the direction opposite to the jet motion. Therefore, gamma-rays, produced in blob II, can be emitted at relatively large angles to the jet axis in the observer’s reference frame. We analyze the basic emission features of such an external blob radiation model. The example modeling of the emission from the FR I type radio galaxy, NGC 1275, is presented.

Radioisotopic purity and imaging properties of cyclotron-produced 99mTc using direct 100Mo(p,2n) reaction

Evaluation of the radioisotopic purity of technetium-99m (99mTc) produced in GBq amounts by proton bombardment of enriched molibdenum-100 (100Mo) metallic targets at low proton energies (i.e. within 15–20 MeV) is conducted. This energy range was chosen since it is easily achievable by many conventional medical cyclotrons already available in the nuclear medicine departments of hospitals. The main motivation for such a study is in the framework of the research activities at the international level that have been conducted over the last few years to develop alternative production routes for the most widespread radioisotope used in medical imaging. The analysis of technetium isotopes and isomeric states (9xTc) present in the pertechnetate saline Na99mTcO4 solutions, obtained after the extraction/purification procedure, reveals radionuclidic purity levels basically in compliance with the limits recently issued by European Pharmacopoeia 9.3 (2018 Sodium pertechnetate (99mTc) injection 4801–3). Moreover, the impact of 9xTc contaminant nuclides on the final image quality is thoroughly evaluated, analyzing the emitted high-energy gamma rays and their influence on the image quality. The spatial resolution of images from cyclotron-produced 99mTc acquired with a mini-gamma camera was determined and compared with that obtained using technetium-99m solutions eluted from standard 99Mo/99mTc generators. The effect of the increased image background contribution due to Compton-scattered higher-energy gamma rays (Eγ > 200 keV), which could cause image-contrast deterioration, was also studied. It is concluded that, due to the high radionuclidic purity of cyclotron-produced 99mTc using 100Mo(p,2n)99mTc reaction at a proton beam energy in the range 15.7–19.4 MeV, the resulting image properties are well comparable with those from the generator-eluted 99mTc.

Nonthermal Emission from Stellar Bow Shocks

Abstract Since the detection of nonthermal radio emission from the bow shock of the massive runaway star BD +43°3654, simple models have predicted high-energy emission, at X-rays and gamma-rays, from these Galactic sources. Observational searches for this emission so far give no conclusive evidence but a few candidates at gamma-rays. In this work we aim at developing a more sophisticated model for the nonthermal emission from massive runaway star bow shocks. The main goal is to establish whether these systems are efficient nonthermal emitters, even if they are not strong enough yet to be detected. For modeling the collision between the stellar wind and the interstellar medium we use 2D hydrodynamic simulations. We then adopt the flow profile of the wind and the ambient medium obtained with the simulation as the plasma state for solving the transport of energetic particles injected in the system, as well as the nonthermal emission they produce. For this purpose we solve a 3D (two spatial + energy) advection-diffusion equation in the test-particle approximation. We find that a massive runaway star with a powerful wind converts 0.16%–0.4% of the power injected in electrons into nonthermal emission, mostly produced by inverse Compton scattering of dust-emitted photons by relativistic electrons, and second by synchrotron radiation. This represents a fraction of ∼10−5 to 10−4 of the wind kinetic power. Given the better sensibility of current instruments at radio wavelengths, these systems are more prone to be detected at radio through the synchrotron emission they produce rather than at gamma energies.

Physics of Pair Producing Gaps in Black Hole Magnetospheres

Abstract In some low-luminosity accreting supermassive black hole systems, the supply of plasma in the funnel region can be a problem. It is believed that a local region with an unscreened electric field can exist in the black hole magnetosphere, accelerating particles and producing high-energy gamma-rays that can create e ± pairs. We carry out time-dependent self-consistent 1D PIC simulations of this process, including inverse-Compton scattering and photon tracking. We find a highly time-dependent solution where a macroscopic gap opens quasi-periodically to create e ± pairs and high-energy radiation. If this gap is operating at the base of the jet in M87, we expect an intermittency on the order of a few r g /c, which coincides with the timescale of the observed TeV flares from the same object. For Sagittarius A* the gap electric field can potentially grow to change the global magnetospheric structure, which may explain the lack of a radio jet at the center of our galaxy.