High-energy Photon Production Research Articles

Development of a bright MeV photon source with compound parabolic concentrator targets on the National Ignition Facility Advanced Radiographic Capability (NIF-ARC) laser

Compound parabolic concentrator (CPC) targets are utilized at the National Ignition Facility Advanced Radiographic Capability (NIF-ARC) laser to enhance the acceleration of electrons and production of high energy photons, for laser durations of 10 ps and energies up to 2.4 kJ. A large enhancement of mean electron energy (>2 ×) and photon brightness (>10×) is found with CPC targets compared to flat targets. Using multiple diagnostic techniques at different spatial locations and scaling by gold activation spatial data, photon spectra are characterized for Ephoton=0.5–30 MeV. Beam width and pointing variations are given. The efficient production of MeV photons at Ilaser≈2×1018 W/cm2 with CPCs is observed, with doses of >10 rad in air at 1 m for Ephoton>0.5 MeV; these exceed those previously reported with laser-driven sources. Using this source, sub-mm resolution radiographs are generated through large areal density radiograph objects. These results are promising for the development of bright MeV x-ray and particle sources on Petawatt class laser systems.

Role of Van Hove singularities and effective mass anisotropy in polarization-resolved high harmonic spectroscopy of silicon

Nonlinear optical response of materials exposed to strong nonresonant light fields leads to production of high energy photons whose spectra contain fingerprints of the coherent electron dynamics in the material. In this paper we investigate how the high harmonic spectra generated in crystalline silicon are linked to specific properties of its band structure. By comparing the polarization anisotropy of high harmonic spectra for two distinct frequencies of the driving pulses we show that the anisotropy has two sources. When driven by mid-infrared light, the signal at specific photon energies is enhanced by the presence of Van Hove singularities in the joint density of states of silicon. With near-infrared driving pulses, in contrast, the high harmonic yield is mainly influenced by the anisotropy of the reduced mass of electron-hole pair, which is related to the nonresonant excitation probability. The experimental results are compared with numerical calculations using time-dependent density functional theory.

Efficient high-energy photon production in the supercritical QED regime

When dense high-energy lepton bunches collide, the beam particles can experience rest-frame electromagnetic fields which greatly exceed the QED critical one. Here it is demonstrated that beamstrahlung efficiently converts lepton energy to high-energy photons in this so-called supercritical QED regime, as the single-photon emission spectrum exhibits a pronounced peak close to the initial lepton energy. It is also shown that the observation of this high-energy peak in the photon spectrum requires one to mitigate multiple photon emissions during the interaction. Otherwise, the photon recoil induces strong correlations between subsequent emissions which soften the photon spectrum and suppress the peak. The high-energy peak in the photon spectrum constitutes a unique observable of photon emission in the supercritical QED regime and provides decisive advantages for the realization of an efficient multi-TeV laserless gamma-gamma collider based on electron-electron collisions.

Atomic-like high-harmonic generation from two-dimensional materials.

The generation of high-order harmonics from atomic and molecular gases enables the production of high-energy photons and ultrashort isolated pulses. Obtaining efficiently similar photon energy from solid-state systems could lead, for instance, to more compact extreme ultraviolet and soft x-ray sources. We demonstrate from ab initio simulations that it is possible to generate high-order harmonics from free-standing monolayer materials, with an energy cutoff similar to that of atomic and molecular gases. In the limit in which electrons are driven by the pump laser perpendicularly to the monolayer, they behave qualitatively the same as the electrons responsible for high-harmonic generation (HHG) in atoms, where their trajectories are described by the widely used semiclassical model, and exhibit real-space trajectories similar to those of the atomic case. Despite the similarities, the first and last steps of the well-established three-step model for atomic HHG are remarkably different in the two-dimensional materials from gases. Moreover, we show that the electron-electron interaction plays an important role in harmonic generation from monolayer materials because of strong local-field effects, which modify how the material is ionized. The recombination of the accelerated electron wave packet is also found to be modified because of the infinite extension of the material in the monolayer plane, thus leading to a more favorable wavelength scaling of the harmonic yield than in atomic HHG. Our results establish a novel and efficient way of generating high-order harmonics based on a solid-state device, with an energy cutoff and a more favorable wavelength scaling of the harmonic yield similar to those of atomic and molecular gases. Two-dimensional materials offer a unique platform where both bulk and atomic HHG can be investigated, depending on the angle of incidence. Devices based on two-dimensional materials can extend the limit of existing sources.

Photon production in Pb + Pb collisions at [formula omitted] TeV

We calculate the high energy photon production from the Pb + Pb collisions for different centrality classes at sNN=2.76 TeV Large Hadron Collider (LHC) energy. The jet energy loss in the jet fragmentation, jet-photon conversion and jet bremsstrahlung is considered by using the Wang–Huang–Sarcevic (WHS) and Baier–Dokshitzer–Mueller–Peigne–Schiff (BDMPS) models. We use the (1+1)-dimensional ideal relativistic hydrodynamics to study the collective transverse flow and space–time evolution of the quark gluon plasma (QGP). The numerical results agree well with the ALICE data of the direct photons from the Pb + Pb collisions (sNN=2.76 TeV) for 0–20%, 20–40% and 40–80% centrality classes.

Enhanced, high energy photon production from resonant Compton scattering in a strong external field

A theoretical and phenomenological consideration is given to higher order, strong field effects in electron/laser interactions. A consistent strong field theory is the Furry interaction picture of intense field quantum field theory. In this theory, fermions are embedded in the strong laser field and the Volkov wavefunction solutions that result, are exact with respect to the strong field. When these Volkov fermions interact with individual photons from other sources, the transition probability is enhanced in a series of resonances when the kinematics allow the virtual fermion to go on-shell. An experiment is proposed in which, for the first time, resonances could be used to generate high energy photons from relativistic electrons at rates orders of magnitude in excess of usual mechanisms.

Strong-field ionization of clusters using two-cycle pulses at 1.8 μm.

The interaction of intense laser pulses with nanoscale particles leads to the production of high-energy electrons, ions, neutral atoms, neutrons and photons. Up to now, investigations have focused on near-infrared to X-ray laser pulses consisting of many optical cycles. Here we study strong-field ionization of rare-gas clusters (103 to 105 atoms) using two-cycle 1.8 μm laser pulses to access a new interaction regime in the limit where the electron dynamics are dominated by the laser field and the cluster atoms do not have time to move significantly. The emission of fast electrons with kinetic energies exceeding 3 keV is observed using laser pulses with a wavelength of 1.8 μm and an intensity of 1 × 1015 W/cm2, whereas only electrons below 500 eV are observed at 800 nm using a similar intensity and pulse duration. Fast electrons are preferentially emitted along the laser polarization direction, showing that they are driven out from the cluster by the laser field. In addition to direct electron emission, an electron rescattering plateau is observed. Scaling to even longer wavelengths is expected to result in a highly directional current of energetic electrons on a few-femtosecond timescale.

HARD X-RAY EMISSIONS FROM CASSIOPEIA A OBSERVED BY INTEGRAL

ABSTRACT Cassiopeia A (Cas A), as the nearby young remnant of a core-collapse supernova, is the best candidate for astrophysical studies in supernova explosion and its environment. We studied the hard X-ray emission from Cas A using the 10 year data of INTEGRAL observations, and first detected non-thermal continuum emission from the source up to 220 keV. The 44Ti line emission at 68 and 78 keV is confirmed by our observations with a mean flux of ∼(2.2 ± 0.4) × 10−5 ph cm−2 s−1, corresponding to a 44Ti yield in Cas A of (1.3 ± 0.4) × 10−4 M ⊙. The continuum emission from 3 to 500 keV can be fit with a thermal bremsstrahlung of kT ∼ 0.79 ± 0.08 keV plus a power-law model of Γ ∼ 3.13 ± 0.03. The non-thermal emission from Cas A is well fit by a power-law model without a cutoff up to 220 keV. This radiation characteristic is inconsistent with diffusive shock acceleration models with a remnant shock velocity of only 5000 km s−1. The central compact object in Cas A cannot significantly contribute to the emission above 80 keV. Some possible physical origins of the non-thermal emission above 80 keV from the remnant shock are discussed. We deduce that the asymmetrical supernova explosion scenario of Cas A is a promising scenario for the production of high-energy synchrotron radiation photons, where a portion of the ejecta with a velocity of ∼0.1c and opening angle of ∼10° can account for the 100 keV emission, as is consistent with the “jet” observed in Cas A.

Photon and dilepton production from a non-equilibrium quark-gluon plasma

We calculate leading-order medium photon and dilepton yields from a quark-gluon plasma using (3+1)-dimensional anisotropic hydrodynamics. In the case of dileptons, at leading-order it is sufficient to take into account non-equilibrium corrections to the rate through the use of anisotropic distribution functions. In the case of photons, non-equilibrium corrections to the rate are taken into account using a self-consistent modification of the distribution functions and the corresponding anisotropic hard-loop quark self-energies. We present predictions for the high-energy photon and dilepton spectrum and the photon elliptic flow as a function of invariant mass, transverse momentum, shear viscosity, and initial momentum-space anisotropy. Our findings indicate that both high-energy photon and dilepton production are sensitive to the assumed level of initial momentum-space anisotropy of the quark-gluon plasma. In addition, we find that the photon elliptic flow depends on the initial momentum-space anisotropy.

Modeling nonthermal emission from stellar bow shocks

Runaway O- and early B-type stars passing throughout the interstellar medium at supersonic velocities and characterized by strong stellar winds may produce bow shocks that can serve as particle acceleration sites. Previous theoretical models predict the production of high energy photons by non-thermal radiative processes, but their efficiency is still debated. We aim to test and explain the possibility of emission from the bow shocks formed by runaway stars traveling through the interstellar medium by using previous theoretical models. We apply our model to AE Aurigae, the first reported star with an X-ray detected bow shock, to BD+43 3654, in which the observations failed in detecting high energy emission, and to the transition phase of a supergiant star in the late stages of its life.From our analysis, we confirm that the X-ray emission from the bow shock produced by AE Aurigae can be explained by inverse Compton processes involving the infrared photons of the heated dust. We also predict low high energy flux emission from the bow shock produced by BD+43 3654, and the possibility of high energy emission from the bow shock formed by a supergiant star during the transition phase from blue to red supergiant.Bow shock formed by different type of runaway stars are revealed as a new possible source of high energy photons in our neighbourhood.

Photon production from a nonequilibrium quark-gluon plasma

We calculate leading-order medium photon yields from a quark-gluon plasma using (3+1)-dimensional anisotropic hydrodynamics. Non-equilibrium corrections to the photon rate are taken into account using a self-consistent modification of the particle distribution functions and the corresponding anisotropic hard-loop fermionic self-energies. We present predictions for the high-energy photon spectrum and photon elliptic flow as a function of transverse momentum, shear viscosity, and initial momentum-space anisotropy. Our findings indicate that high-energy photon production is sensitive to the assumed level of initial momentum-space anisotropy of the quark-gluon plasma. As a result, it may be possible to experimentally constrain the early-time momentum-space anisotropy of the quark-gluon plasma generated in relativistic heavy-ion collisions using high-energy photon yields.

Neutron–proton bremsstrahlung as a possible probe of high-momentum component in nucleon momentum distribution

Abstract Neutron-proton bremsstrahlung in intermediate energy nucleus–nucleus collisions is proposed as a possible probe to study the high-momentum component in nucleon momentum distribution of finite nucleus. Based on the Boltzmann–Uehling–Uhlenbeck (BUU) transport model, the effects of high-momentum component on the production of bremsstrahlung photons in the reaction of C 12 + 12 C collisions at different incident beam energies are studied. It is found that the high-momentum component increases the high-energy bremsstrahlung photon production remarkably. Furthermore, the ratio of photon production at different incident beam energies is suggested as a potential observable to probe the high-momentum component in nucleon momentum distribution of finite nucleus.

A systematic synchro-curvature modelling of pulsar γ-ray spectra unveils hidden trends

$\gamma$-ray radiation from pulsars is usually thought to be mostly produced by the synchro-curvature losses of accelerated particles. Here we present a systematic study of all currently reported, good-quality Fermi-LAT pulsar spectral data. We do so by applying a model which follows the particle dynamics and consistently computes the emission of synchro-curvature radiation. By fitting observational data on a case by case basis, we are able to obtain constraints about the parallel electric field, the typical lengthscale over which particles emit the bulk of the detected radiation, and the number of involved particles. The model copes well with data of several dozens of millisecond and young pulsars. By correlating the inferred model parameters with the observed timing properties, some trends are discovered. First, a non-negligible part of the radiation comes from the loss of perpendicular momentum soon after pair creation. Second, the electric field strongly correlates with both the inverse of the emission lengthscale and the magnetic field at light cylinder, thus ruling out models with high-energy photon production close to the surface. These correlations unify young and millisecond pulsars under the same physical scenario, and predict that magnetars are intrinsically $\gamma$-ray quiet via syncrhro-curvature processes, since magnetospheric particles are not accelerated enough to emit a detectable $\gamma$-ray flux.

Photoionization analysis of chemodynamical dwarf galaxies simulations

Photoionization modelling allows to follow the transport, the emergence, and the absorption of photons taking into account all important processes in nebular plasmas. Such modelling needs the spatial distribution of density, chemical abundances and temperature, that can be provided by chemo-dynamical simulations (ChDS) of dwarf galaxies. We perform multicomponent photoionization modelling (MPhM) of the ionized gas using 2-D ChDSs of dwarf galaxies. We calculate emissivity maps for important nebular emission lines. Their intensities are used to derive the chemical abundance of oxygen by the so-called Te- and R23-methods. Some disagreements are found between oxygen abundances calculated with these methods and the ones coming from the ChDSs. We investigate the fraction of ionizing radiation emitted in the star-forming region which is able to leak out the galaxy. The time- and direction-averaged escape fraction in our simulation is 0.35-0.4. Finally, we have calculated the total Halpha lumi- nosity of our model galaxy using Kennicutt's calibration to derive the star-formation rate. This value has been compared to the 'true' rate in the ChDSs. The Halpha-based star-formation rate agrees with the true one only at the beginning of the simulation. Minor deviations arise later on and are due in part to the production of high-energy photons in the warm-hot gas, in part to the leakage of energetic photons out of the galaxy. The effect of artificially introduced thin dense shells (with thicknesses smaller than the ChDSs spatial resolution) is investigated, as well.

The jet of the quasar 4C+21.35 from parsec to kiloparces scales and its role in high energy photon production

AbstractWe present an analysis of the parsec-scale jet structure of the quasar 4C+21.35 with a resolution of 0.1 milliarcseconds based on 63 epochs of Very Long Baseline Array observations at 43 GHz from 2007 June to 2014 May along with the Fermi LAT γ-ray light curve and multi-frequency optical photometric and polarimetric data. We find that the innermost jet of the quasar consists of a very compact core of size ~0.03 mas, as well as feature A1 located 0.16 ± 0.03 mas from the core. The distance of A1 remains fairly stable, but its position angle with respect to the core changes from -10 to +10 deg. We detect 4 superluminal knots in the inner jet with apparent speeds ranging from 10c to 20c. The first two components appeared in the jet during the high γ-ray state of the quasar from mid-2010 to early 2011, while the fourth knot appears to be connected with the γ-ray active state in late 2013 - early 2014. The first knot can be associated with the dramatic VHE flare in 2010 June and possesses an extreme Doppler factor ~60. We find that maxima in the γ-ray light curve coincide with epochs of interaction between the moving knots and the core and feature A1. This suggests that the core and A1 are recollimation shocks where γ-ray flares occur. The Chandra 0.5-6 keV image reveals the existence of X-ray emission in the kiloparsec scale jet of the quasar that can be explained via inverse Compton scattering off the cosmic microwave background by relativistic electrons if no deceleration occurs between the parsec- and kiloparsec-scale jets.

AE AURIGAE: FIRST DETECTION OF NON-THERMAL X-RAY EMISSION FROM A BOW SHOCK PRODUCED BY A RUNAWAY STAR

Runaway stars produce shocks when passing through interstellar medium at supersonic velocities. Bow shocks have been detected in the mid-infrared for several high-mass runaway stars and in radio waves for one star. Theoretical models predict the production of high-energy photons by non-thermal radiative processes in a number sufficiently large to be detected in X-rays. To date, no stellar bow shock has been detected at such energies. We present the first detection of X-ray emission from a bow shock produced by a runaway star. The star is AE Aur, which was likely expelled from its birthplace by the encounter of two massive binary systems and now is passing through the dense nebula IC 405. The X-ray emission from the bow shock is detected at 30" to the northeast of the star, coinciding with an enhancement in the density of the nebula. From the analysis of the observed X-ray spectrum of the source and our theoretical emission model, we confirm that the X-ray emission is produced mainly by inverse Compton upscattering of infrared photons from dust in the shock front.

Compact Storage Ring with Longitudinal Magnetic Field and Electron Cooling

Project of compact low energy proton storage ring (1.75 MeV) for production of high energy photons in reaction 13C(p,γ) 14N on internal target is presented. With the help of the photons it is possible to realize the scheme for detection of substances with heightened content of nitrogen using Nuclear Resonance Absorption method. Distinctive features of the construction are use of electron cooling method for beam heating compensation, and strong longitudinal magnetic field along full perimeter of the ring. For optimal work of electron cooling, compensation of space charge of the beam circulating in the ring is necessary. Results of simulation of main effects in the storage ring are shown. The results allow us to expect that proton current up to 100 mA can be stored and luminosity up to 3·1033 cm2 s -1 can be achieved

Evolution of the parsec-scale jet in 3C 345

AbstractThe 16m quasar 3C 345 is one of the best examples of an AGN showing structural and flux variability on parsec scales around a compact unresolved radio core. It has been observed from radio to γ-ray wavebands with a special focus on Very Long Baseline Interferometry (VLBI) observations in the range 1-100 GHz that cover a period of over 30 years. The complex pc-scale jet of 3C 345 exemplifies an archetypal “superluminal” jet with helical substructure. Existing VLBI observations of 3C 345 form an unprecedented database enabling a unique insight into the long-term evolution of the pc-scale radio emission. Here we present the latest results from our ongoing long-term VLBI monitoring of 3C 345, focusing on the morphological, kinematic, and spectral evolution of the pc-scale jet. Special attention will be given to the recent onset of a new period of high activity in the source that has been manifesting itself since 2008 from radio through γ-rays. Recent VLBI and high energy observations to study the relation between the radio emission and the production of high energy photons in 3C 345 are combined.

Neutrinos from photo-hadronic interactions in Pks2155-304

The high-peaked BL Lac object Pks2155-304 shows high variability at multiwavelengths, i.e. from optical up to TeV energies. A giant flare of around 1 h at X-ray and TeV energies was observed in 2006 [1]. In this context, it is essential to understand the physical processes in terms of the primary spectrum and the radiation emitted, since high-energy emission can arise in both leptonic and hadronic processes. In this contribution, we investigate the possibility of neutrino production in photo-hadronic interactions. In particular, we predict a direct correlation between optical and TeV energies at sufficiently high optical radiation fields. We show that in the blazar Pks2155-304, the optical emission in the low-state is sufficient to lead to photo-hadronic interactions and therefore to the production of high-energy photons.

Gamma ray observation from ground

Nowadays the Gamma ray observation of the sky is opening an important window to understand the nature of high-energy phenomena in the Universe and provides important tools to test fundamental physics that is constrained in the production and propagation of high-energy photons. The observation of gamma ray from ground is playing an important role: the success of the running ground based experiments shows that the large collection area and the high sensitivity to the high energy domains makes the gamma ray observation from ground complementary to the satellite one, and in many cases fundamental for a large class of scientific investigation. In this paper the main ground based gamma ray running experiment are reviews and a glance of the perspective in this field is given.