High-energy Spectra Research Articles

Exploring calorimetry new dimensions: a novel approach to maximize the performances of space experiments for high-energy cosmic rays

Calorimeters are the key detectors for future space based experiments focused on high-energy cosmic rays spectra measurements. Thus it is extremely important to optimize their geometrical design, granularity and absorption depth, with respect to the total mass of the apparatus, which is among the most important constraints for a space mission. CaloCube is a homogeneous calorimeter whose basic geometry is cubic and isotropic, so as to detect particles arriving from every direction in space, thus maximizing the acceptance; granularity is obtained by filling the cubic volume with small cubic scintillating crystals. A prototype, instrumented with CsI(Tl) cubic crystals, has been constructed and tested with particle beams.

Upscattered Cocoon Emission in Short Gamma-Ray Bursts as High-energy Gamma-Ray Counterparts to Gravitational Waves

Abstract We investigate prolonged engine activities of short gamma-ray bursts (SGRBs), such as extended and/or plateau emissions, as high-energy gamma-ray counterparts to gravitational waves (GWs). Binary neutron-star mergers lead to relativistic jets and merger ejecta with r-process nucleosynthesis, which are observed as SGRBs and kilonovae/macronovae, respectively. Long-term relativistic jets may be launched by the merger remnant as hinted in X-ray light curves of some SGRBs. The prolonged jets may dissipate their kinetic energy within the radius of the cocoon formed by the jet–ejecta interaction. Then the cocoon supplies seed photons to nonthermal electrons accelerated at the dissipation region, causing high-energy gamma-ray production through the inverse Compton scattering process. We numerically calculate high-energy gamma-ray spectra in such a system using a one-zone and steady-state approximation, and show that GeV–TeV gamma-rays are produced with a duration of 102–105 s. They can be detected by Fermi/LAT or CTA as gamma-ray counterparts to GWs.

Unfolding of sparse high-energy γ-ray spectra from LaBr3:Ce detectors

Here we report on the characterization of one of the large-volume LaBr3:Ce detectors for the ELIGANT project at ELI-NP. The main focus of this work is the response function for high-energy γ rays of such detectors. In particular, we compare a selection of unfolding methods to resolve small structures in γ-ray spectra with high-energies. Three methods have been compared using γ-ray spectra with energies up to 12 MeV obtained in an experiment at the 3 MV TandetronTM facility at IFIN-HH. The results show that the iterative unfolding approach gives the best qualitative reproduction of the emitted γ-ray spectrum. Furthermore, the correlation fluctuations in high-energy regime from the iterative method are two orders of magnitude smaller than when using the matrix inversion approach with second derivative regularization. In addition, the iterative method is computationally faster as it does not contain large matrix inversions. The matrix inversion method does, however, give more consistent results over the full energy range and in the low-statistics limit. Our conclusion is that the performance of the iterative approach makes it well suitable for semi-online analysis of experimental data. These results will be important, both for experiments with the ELIGANT setup, and for on-line diagnostics of the energy spread of the γ-ray beam which is under implementation at ELI-NP.

Convergence Rates for Quantum Evolution and Entropic Continuity Bounds in Infinite Dimensions

By extending the concept of energy-constrained diamond norms, we obtain continuity bounds on the dynamics of both closed and open quantum systems in infinite dimensions, which are stronger than previously known bounds. We extensively discuss applications of our theory to quantum speed limits, attenuator and amplifier channels, the quantum Boltzmann equation, and quantum Brownian motion. Next, we obtain explicit log-Lipschitz continuity bounds for entropies of infinite-dimensional quantum systems, and classical capacities of infinite-dimensional quantum channels under energy-constraints. These bounds are determined by the high energy spectrum of the underlying Hamiltonian and can be evaluated using Weyl’s law.

Constraints on Gamma-Ray and Neutrino Emission from NGC 1068 with the MAGIC Telescopes

Abstract Starburst galaxies and star-forming active galactic nuclei are among the candidate sources thought to contribute appreciably to the extragalactic gamma-ray and neutrino backgrounds. NGC 1068 is the brightest of the star-forming galaxies found to emit gamma-rays from 0.1 to 50 GeV. Precise measurements of the high-energy spectrum are crucial to study the particle accelerators and probe the dominant emission mechanisms. We have carried out 125 hr of observations of NGC 1068 with the MAGIC telescopes in order to search for gamma-ray emission in the very-high-energy band. We did not detect significant gamma-ray emission, and set upper limits at the 95% confidence level to the gamma-ray flux above 200 GeV f < 5.1 × 10−13 cm−2 s−1. This limit improves previous constraints by about an order of magnitude and allows us to put tight constraints on the theoretical models for the gamma-ray emission. By combining the MAGIC observations with the Fermi-LAT spectrum we limit the parameter space (spectral slope, maximum energy) of the cosmic ray protons predicted by hadronuclear models for the gamma-ray emission, while we find that a model postulating leptonic emission from a semi-relativistic jet is fully consistent with the limits. We provide predictions for IceCube detection of the neutrino signal foreseen in the hadronic scenario. We predict a maximal IceCube neutrino event rate of 0.07 yr−1.

The Acceleration of Energetic Particles at Coronal Shocks and Emergence of a Double Power-law Feature in Particle Energy Spectra

Abstract We present numerical modeling of particle acceleration at coronal shocks propagating through a streamer-like magnetic field by solving the Parker transport equation with spatial diffusion both along and across the magnetic field. We show that the location on the shock where the high-energy particle intensity is the largest, depends on the energy of the particles and on time. The acceleration of particles to more than 100 MeV mainly occurs in the shock-streamer interaction region, due to perpendicular shock geometry and the trapping effect of closed magnetic fields. A comparison of the particle spectra to that in a radial magnetic field shows that the intensity at 100 MeV (200 MeV) is enhanced by more than one order (two orders) of magnitude. This indicates that the streamer-like magnetic field can be an important factor in producing large solar energetic particle events. We also show that the energy spectrum integrated over the simulation domain consists of two different power laws. Further analysis suggests that it may be a mixture of two distinct populations accelerated in the streamer and open field regions, where the acceleration rate differs substantially. Our calculations also show that the particle spectra are affected considerably by a number of parameters, such as the streamer tilt angle, particle spatial diffusion coefficient, and shock compression ratio. While the low-energy spectra agree well with standard diffusive shock acceleration theory, the break energy ranges from ∼1 MeV to ∼90 MeV and the high-energy spectra can extend to ∼1 GeV with a slope of ∼2–3.

Spectral Lag for a Radiating Jet Shell with a High-energy Cutoff Radiation Spectrum

Abstract Recent research shows that the spectral lag is closely related to the spectral evolution in gamma-ray bursts (GRBs). In this paper, we study the spectral lag for a radiating jet shell with a high-energy cutoff radiation spectrum. For the jet shell with a cutoff power-law spectrum, the spectral lag monotonically increases with the photon energy and levels off at a certain photon energy. It is the same for the jet shell with a Band cutoff spectrum (Bandcut). However, a turnover from the positive lags to negative lags appears in the high-energy range for the jet shell with a Bandcut, which is very similar to that observed in GRB 160625B. The dependence of the spectral lags on the spectral shape/evolution is studied in detail. In addition, the spectral lag behavior observed in GRB 160625B is naturally reproduced based on our theoretical outcome.

Analysis of Photo Neutron Dose to Patient from a 15 MV Linear Accelerator

Medical Linear Accelerator produces high-intensity bremsstrahlung beam, with typical energy ranges from 4 to 18MV for treatment purposes. The materials including patient exposed to this high energy spectrum lead to a photonuclear reaction in them. In these Photon energy domains, photo neutron production (n, p, and γ, n) is the major reaction channel. This is important as Carbon, Oxygen, Hydrogen, and Nitrogen are the predominant elements in a typical human being and having low photon neutron threshold. Apart from this, the equipment involved in a radiation treatment including Head, Couch, immobilization accessories, etc contributes to photo neutron production. The present study was recorded and analyzed the photo neutron spectra due to 15 MV medical linear accelerator using CR-39 Solid State Nuclear Track Detector and image processing software.

Examination of Calculations of the Atmospheric Muon and Neutrino Spectra Using New Measurements

The atmospheric muon and neutrino fluxes at energies from 10 GeV to 10 PeV are calculated with the Kimel–Mokhov (KM), SIBYLL 2.1, EPOS LHC, and QGSJET-II hadronic models for known parameterizations of the cosmic ray spectra by Zatsepin--Sokolskaya and Hillas–Gaisser. The calculations with the KM, EPOS LHC, and SIBYLL 2.1 models are agree well with the measurements of the atmospheric muon spectra in IceCube and IceTop experiments. The measurement of high-energy muon spectra indicates the presence of the prompt muon component at energies above 500 TeV, which is well reproduced in calculations with the quark-gluon string model. The calculations of the atmospheric muon neutrino spectrum performed for the KM, EPOS LHC, and SIBYLL 2.1 models give good fit with the measurement data of IceCube, ANTARES, and Super-Kamiokande experiments.

Electron Polarimetry with Nonlinear Compton Scattering

Impacts of spin-polarization of an ultrarelativistic electron beam head-on colliding with a strong laser pulse on emitted photon spectra and electron dynamics have been investigated in the quantum radiation regime. We simulate photon emissions quantum mechanically and electron dynamics semiclassically via taking spin-resolved radiation probabilities in the local constant field approximation. A small ellipticity of the laser field brings about an asymmetry in angle-resolved photon spectrum, which sensitively relies on the polarization of the electron beam. The asymmetry is particularly significant in high-energy photon spectra, and is employed for the polarization detection of a high-energy electron beam with extraordinary precision, e.g., better than 0.3\% for a few-GeV electron beam at a density of the scale of $10^{16}$ cm$^{-3}$ with currently available strong laser fields. This method demonstrates for the first time a way of single-shot determination of polarization for ultrarelativistic electron beams via nonlinear Compton scattering. A similar method based on the asymmetry in the electron momentum distribution after the interaction due to spin-dependent radiation reaction is proposed as well.

Applications of dual energy CT in clinical practice: A pictorial essay.

In dual-energy CT (DECT), two different x-ray spectra are used to acquire two image datasets of the same region, to allow the analysis of energy-dependent changes in the attenuation of different materials. Each type of material demonstrates a relatively specific change in attenuation between images obtained with a high-energy spectrum and those obtained with a low-energy spectrum. Based on the relatively specific change in attenuation with two different energies, material composition information can be obtained to allow tissue characterization. The DECT ability of material differentiation allows bone removal in various CT angiography studies and bone marrow edema depiction, while with material optimization, metal artefacts can be significantly reduced to almost nil. DECT allows material separation to differentiate uric acid crystals from calcium to determine the composition of urinary calculi and to diagnose gout. Using the DECT ability of material decomposition, iodine maps can be generated, which are useful in the evaluation of any enhancing lesion in the body without the need to obtain a plain scan and allow perfusion maps to be created in cases of pulmonary thromboembolism.

Inverse Compton Scattering Spectra of Gamma-Ray Burst Prompt Emission

Abstract Although the physical origin of gamma-ray burst (GRB) prompt emission is still controversial, synchrotron radiation from accelerated electrons is a promising mechanism. It is believed that electrons are accelerated continuously by ultra-relativistic shocks or magnetic reconnections. At the same time, these electrons will be cooled via several processes (mainly adiabatic expansion, synchrotron radiation, and inverse Compton scattering (ICS)), which regulate the distribution of electrons. An extra high-energy spectrum component is expected to be induced by ICS. However, the gamma–gamma annihilation effect may eliminate the high-energy photons and prevent the observers from distinguishing the extra component. We perform numerical calculations by taking these effects into account and discuss whether the extra ICS component could be observed. By exploring the plausible parameter space for relevant quantities of the GRB ejecta, we present the electron distributions and the corresponding spectra of synchrotron radiation and ICS. It is found that the extra component is observable only for ejecta with a rather large bulk Lorentz factor. A large Lorentz factor means the adiabatic expansion is the leading process in the electron cooling procedure, which makes the low-energy electron distribution spectrum relatively hard. Therefore, the ICS component is more likely to be detected for GRBs that have a hard low-energy photon spectrum.

Contact and Sum Rules in a Near-Uniform Fermi Gas at Unitarity

We present an experimental study of the high-energy excitation spectra of unitary Fermi gases. Using focused beam Bragg spectroscopy, we locally probe atoms in the central region of a harmonically trapped cloud where the density is nearly uniform, enabling measurements of the dynamic structure factor for a range of temperatures both below and above the superfluid transition. Applying sum rules to the measured Bragg spectra, we resolve the characteristic behavior of the universal contact parameter, C, across the superfluid transition. We also employ a recent theoretical result for the kinetic (second-moment) sum rule to obtain the internal energy of gases at unitarity.

Effects of Synchrotron Cooling and Pair Production on Collisionless Relativistic Reconnection

Abstract High-energy radiation from nonthermal particles accelerated in relativistic magnetic reconnection is thought to be important in many astrophysical systems, ranging from blazar jets and black hole accretion disk coronae to pulsars and magnetar flares. The presence of a substantial density of high-energy photons (>MeV) in these systems can make two-photon pair production (γγ → e − e +) an additional source of plasma particles and can affect the radiative properties of these objects. We present the results of novel particle-in-cell simulations that track both the radiated synchrotron photons and the created pairs, with which we study the evolution of a two-dimensional reconnecting current sheet in pair plasma. Synchrotron radiation from accelerated particles in the current sheet produces hot secondary pairs in the upstream, which are later advected into the current sheet where they are reaccelerated and produce more photons. In the optically thin regime, when most of the radiation is leaving the upstream unaffected, this process is self-regulating and depends only on the background magnetic field and the optical depth of photons to pair production. The extra plasma loading also affects the properties of reconnection. We study how the inflow of the secondary plasma, with multiplicities up to several hundred, reduces the effective magnetization of the plasma, suppressing the acceleration and thus decreasing the high-energy photon spectrum cutoff. This offers an explanation for the weak dependence of the observed gamma-ray cutoff in pulsars on the magnetic field at the light cylinder.

A ring of fire in the pulsar magnetosphere

Contopoulos 2019 proposed that a dissipation zone develops in the magnetosphere of young pulsars at the edge of the closed-line region beyond the light cylinder. This is necessary in order to supply the charge carriers that will establish current closure through the equatorial and separatrix current-sheets. In the present work, we propose to investigate in greater detail this region with a simplified model that we would like to call the `ring-of-fire'. According to this simple model, the dissipation zone is a narrow reconnection layer where electrons and positrons are accelerated inwards and outwards respectively along Speiser orbits that are deflected in the azimuthal direction by the pulsar rotation. After they exit the reconnection layer, the accelerated positrons form the positively charged equatorial current-sheet, and the accelerated electrons form the negatively charged separatrix current-sheet along the boundary of the closed-line region. During their acceleration, particles lose only a small part of their energy to radiation. Most of their energy is lost outside the dissipation region, in the equatorial and separatrix current sheets. Our simple model allows us to obtain high-energy spectra and efficiencies. The radiation emitted by the positrons in the equatorial current-sheet forms a very-high energy tail that extends up to the TeV range.

Tomographic Extraction of the Internuclear Separation Based on Two-Center Interference with Aligned Diatomic Molecules.

We experimentally investigate the two-dimensional photoelectron momentum spectra of aligned diatomic molecules in an intense laser field. Our results reveal a novel prominent valley structure in the molecular alignment dependence of the high-energy photoelectron spectra along the laser polarization. Resorting to the molecular strong-field approximation and a simple semiclassical analysis, we show that this valley structure stems from the destructive two-center interference of the laser-driven rescattered electrons in diatomic molecules. Based on this two-center interference with aligned diatomic molecules, we demonstrate for the first time a tomographic method to extract the molecular internuclear separation, providing a more straightforward approach of molecular imaging, in comparison with, e.g., laser-induced electron diffraction and fixed-angle broadband laser-driven electron scattering.

High-order above-threshold ionization of the H2+ ion: The role of internuclear distance

High-order above-threshold ionization (HATI) of the ${{\mathrm{H}}_{2}}^{+}$ ion by a linearly polarized laser field is investigated theoretically using numerical solutions of the full three-dimensional time-dependent Schr\odinger equation (TDSE). The photoelectron spectrum is calculated in two ways: by projecting the final wave function onto continuum states satisfying the incoming boundary condition and by using the window-operator method. Our numerical simulations show that the shape of the corresponding photoelectron energy spectra depends on the internuclear distance. For small internuclear distances the obtained HATI spectrum is very similar to the HATI spectrum for atomic targets. By increasing the internuclear distance, i.e., by stretching the molecule, some features emerge in the spectra. The cutoff position of the high-energy photoelectron spectrum extends from $10{U}_{p}$ (${U}_{p}$ is the electron ponderomotive energy) for small internuclear distances up to above $18{U}_{p}$ for very large internuclear distances. The second observed feature is that, with the increase of the internuclear distance, a low-energy plateau appears which is much higher than the above-mentioned extended plateau. For the internuclear distance of 18 a.u. this plateau extends up to $6{U}_{p}$. These features are further investigated by using solutions of the classical equation of motion for the electron in the strong laser field and by using quantum-orbit theory. The results of classical analysis are confirmed using two quantum-mechanical methods based on the analysis of the electron time-dependent probability density and of the electron energy-resolved probability density, obtained from the TDSE solutions.

Unveiling the origin of the gamma-ray emission in NGC 1068 with the Cherenkov Telescope Array

Several observations are revealing the widespread occurrence of mildly relativistic wide-angle AGN winds strongly interacting with the gas of their host galaxy. Such winds are potential cosmic-ray accelerators, as supported by gamma-ray observations of the nearby Seyfert galaxy NGC 1068 with the Fermi gamma-ray space telescope. The non-thermal emission produced by relativistic particles accelerated by the AGN-driven wind observed in the circum-nuclear molecular disk of such galaxy is invoked to produce the gamma-ray spectrum. The AGN wind model predicts a hard spectrum that extend in the very high energy band which differs significantly from those corresponding to other models discussed in the literature, like starburst or AGN jet. We present dedicated simulations of observations through the Cherenkov Telescope Array (CTA), the next-generation ground based gamma-ray observatory, of the very high energy spectrum of the Seyfert galaxy NGC 1068 assuming the AGN wind and the AGN jet models. We demonstrate that, considering 50 hours of observations, CTA can be effectively used to constrain the two different emission models, providing important insight into the physics governing the acceleration of particles in non-relativistic AGN-driven outflows. This analysis strongly motivates observations of Seyfert and starburst galaxies with CTA in order to test source population models of the extragalactic gamma-ray and neutrino backgrounds.

Extreme hydrodynamic losses of Earth-like atmospheres in the habitable zones of very active stars

Aims. In this Letter, we calculate for the first time the full transonic hydrodynamic escape of an Earth-like atmosphere. We consider the case of an Earth-mass planet with an atmospheric composition identical to that of the current Earth orbiting at 1 AU around a young and very active solar mass star. Methods. To model the upper atmosphere, we used the Kompot Code, which is a first-principles model that calculates the physical structures of the upper atmospheres of planets, taking into account hydrodynamics and the main chemical and thermal processes taking place in the upper atmosphere of a planet. This model enabled us to calculate the 1D vertical structure of the atmosphere using as input the high-energy spectrum of a young and active Sun. Results. The atmosphere has the form of a transonic hydrodynamic Parker wind, which has an outflow velocity at the upper boundary of our computational domain that exceeds the escape velocity. The outflowing gas is dominated by atomic nitrogen and oxygen and their ion equivalents and has a maximum ionization fraction of 20%. The mass outflow rate is found to be 1.8 × 109 g s−1, which would erode the modern Earth’s atmosphere in less than 0.1 Myr. Conclusions. This extreme mass loss rate suggests that an Earth-like atmosphere cannot form when the planet is orbiting within the habitable zone of a very active star. Instead, such an atmosphere can only form after the activity of the star has decreased to a much lower level. This happened in the early atmosphere of the Earth, which was likely dominated by other gases such as CO2. Since the time it takes for the activity of a star to decay is highly dependent on its mass, this is important for understanding possible formation timescales for planets orbiting low-mass stars.

High-energy atmospheric muon flux calculations in comparison with recent measurements

Recently the atmospheric muon spectra at high energies were reconstructed for two ranges of zenith angles, basing on the events collected with the IceCube detector. These measurements reach high energies at which the contribution to atmospheric muon fluxes from decays of short-lived hadrons is expected. Latest IceCube measurements of the high-energy atmospheric muon spectrum indicate the presence of prompt muon component at energies above 500 TeV.