High-energy Photon Production Research Articles

Production of High-Energy Particles in Laser and Coulomb Fields and thee+e−Antenna

A strong laser field and the Coulomb field of a nucleus can produce e(+) e(-) pairs. It is shown for the first time that there is a large probability that electrons and positrons created in this process collide after one or several oscillations of the laser field. These collisions can take place at high energy, resulting in several phenomena. The quasielastic collision e(+) e(-) --> e(+) e(-) allows acceleration of leptons in the laser field to higher energies. The inelastic collisions allow production of high-energy photons e(+) e(-) --> 2 gamma and muons e(+) e(-) --> micro(+) micro(-). The yield of high-energy photons and muons produced via this mechanism exceeds exponentially their production through conventional direct creation in laser and Coulomb fields. A relation of the phenomena considered with the antenna mechanism of multiphoton absorption in atoms is discussed.

Prompt emission of high-energy photons from gamma ray bursts

Within the internal shock scenario, we consider different mechanisms of high-energy ( > 1 MeV) photon production inside a gamma ray burst (GRB ) fireball and derive the expected high-energy photon spectra from individual GRBs during the prompt phase. The photon spectra of leptonic and hadronic origins are compared within different sets of parameter regimes. Our results suggest that the high-energy emission is dominated by the leptonic component if the fraction of shock energy carried by electrons is not very small (e.g. ∈ e > 10 -3 ). For very small values of ∈ e , the hadronic emission component could be comparable to or even exceed the leptonic component in the GeV-TeV regime. However, in this case a much larger energy budget of the fireball is required to account for the same level of the observed sub-MeV spectrum. The fireballs are therefore extremely inefficient in radiation. For a canonical fireball bulk Lorentz factor (e.g. r = 400), emissions above ∼ 10 GeV are attenuated by two-photon pair production processes. For a fireball with an even higher Lorentz factor, the cut-off energy is higher, and emissions of 10 TeV-PeV due to 7r°-decay can also escape from the internal shocks. The flux level is, however, too low to be detected by current TeV detectors, and these photons also suffer attenuation by external soft photons. The GLAST Large Area Telescope can detect prompt emission of bright long GRBs above 100 MeV. For short GRBs, the prompt emission can be only barely detected for nearby bright ones with relatively 'long' durations (e.g. ∼1 s). With the observed high-energy spectrum alone, it appears that there is no clean picture to test the leptonic versus hadronic origin of the gamma rays. Such an issue may be, however, addressed by collecting both prompt and afterglow data. A moderate-to-high radiative efficiency would suggest a leptonic origin of high-energy photons, while a GRB with an extremely low radiative efficiency but an extended high-energy emission component would be consistent with (but not a proof for) the hadronic origin.

Photon production from an anisotropic quark-gluon plasma

We calculate photon production from a quark-gluon plasma which is anisotropic in momentum space including the Compton scattering, $q(\overline{q})g\ensuremath{\rightarrow}q(\overline{q})\ensuremath{\gamma}$, and annihilation, $q\overline{q}\ensuremath{\rightarrow}g\ensuremath{\gamma}$, processes. We show that for a quark-gluon plasma which has an oblate momentum-space anisotropy, $⟨{p}_{L}^{2}⟩<⟨{p}_{T}^{2}⟩$, the photon production rate has an angular dependence which is peaked transverse to the beam line. We propose to use the angular dependence of high-energy medium photon production to experimentally determine the degree of momentum-space isotropy of a quark-gluon plasma produced in relativistic heavy-ion collisions.

Gamma rays from colliding winds of massive stars

Colliding winds of massive binaries have long been considered as potential sites of non-thermal high-energy photon production. This is motivated by the detection of non-thermal spectra in the radio band, as well as by correlation studies of yet unidentified EGRET γ-ray sources with source populations appearing in star formation regions. This work re-considers the basic radiative processes and its properties that lead to high energy photon production in long-period massive star systems. We show that Klein–Nishina effects as well as the anisotropic nature of the inverse Compton scattering, the dominating leptonic emission process, likely yield spectral and variability signatures in the γ-ray domain at or above the sensitivity of current or upcoming gamma ray instruments like GLAST-LAT. In addition to all relevant radiative losses, we include propagation (such as convection in the stellar wind) as well as photon absorption effects, which a priori can not be neglected. The calculations are applied to WR 140 and WR 147, and predictions for their detectability in the γ-ray regime are provided. Physically similar specimen of their kind like WR 146, WR 137, WR 138, WR 112 and WR 125 may be regarded as candidate sources at GeV energies for near-future γ-ray experiments. Finally, we discuss several aspects relevant for eventually identifying this source class as a γ-ray emitting population. Thereby we utilize our findings on the expected radiative behavior of typical colliding wind binaries in the γ-ray regime as well as its expected spatial distribution on the γ-ray sky.

Photon Production in the Parton Cascade Model

We calculate the production of high energy photons from Compton and annihilation processes as well as fragmentation off quarks in the Parton Cascade Model. The multiple scattering of partons is seen to lead to substantial production of high energy photons, which rises further when parton multiplication due to final state radiation is included.

Nonthermal High‐Energy Emission from Colliding Winds of Massive Stars

Colliding winds of massive star binary systems are considered as potential sites of nonthermal high-energy photon production. Motivated by the detection of synchrotron radio emission from the colliding wind location, we here investigate the properties of high-energy photon production in colliding winds of long-period WR+OB systems. Analytical formulae for the steady state proton- and electron-particle spectra are derived assuming diffusive particle accelerationoutofapoolofthermalwindparticles,takinginto account adiabaticand allrelevantradiative losses,and includeadvection/convection out of the wind collision zone. This includes analytical approximations for the electron energy losses in the Klein-Nishina transition regime. For the first time in the context of CWB systems, our calculations use the full Klein-Nishina cross section and account for the anisotropy of the inverse Compton scattering process. This leads to orbitalfluxvariations byupto several orders of magnitude, which may, however,beblurredby the system’s geometry. Both anisotropy and Klein-Nishina effects may yield characteristic spectral and variability signatures in the � -ray domain. Since propagation effects lead to a deficit of low-energy particles in the convectiondominated zone, one expects imprints in the radiation spectra. If protons are accelerated to at least several GeV, � 0 -decay � -rays might be observable, depending on the injected electron-to-proton ratio. We show that photon-photon pair production is generally not negligible, potentially affecting the emitted spectrum above � 50 GeV, depending on orbital phase and system inclination. The calculations are applied to the archetypal WR+OB systems WR 140 and WR 147 to predict their expected spectral and temporal characteristics and to assess their detectability with current and upcoming � -ray experiments. Subject headingg binaries: general — gamma rays: theory — radiation mechanisms: nonthermal — stars: early-type — stars: winds, outflows

Formation length effects in very thin targets

Experimental results for the radiative energy loss of 178GeV positrons in Cu, Au, and W targets are presented. It is shown that for a few micron thick target, effects related to the formation zone disappear, in particular, the suppression due to the Landau-Pomeranchuk-Migdal and Ternovskii-Shul'ga-Fomin mechanisms. This disappearance may restrict the region of applicability of thin foils as a target for energy-selective production of high energy photons. Furthermore, transition radiation dominated by multiple scattering and structured target interference effects are shown to be likely ingredients for an accurate description of the data obtained at low photon energies. © 2005 The American Physical Society.

High-energy photons from passage of jets through Quark-Gluon plasma.

We calculate the production of high-energy photons from Compton scattering and annihilation of a quark jet passing through a quark gluon plasma produced in a relativistic heavy ion collision. The contributions are large and reflect the momentum distribution of the jets and the initial conditions of the plasma.

Light from cascading partons in relativistic heavy-ion collisions.

We calculate the production of high energy photons from Compton and annihilation processes as well as fragmentation off quarks in the parton cascade model. The multiple scattering of partons is seen to lead to a substantial production of high energy photons, which rises further when parton multiplication due to final state radiation is included. The photon yield is found to be directly proportional to the number of hard collisions and thus provides valuable information on the preequilibrium reaction dynamics.

Timing and Spectral Properties of X-Ray Emission from the Converging Flows onto a Black Hole: Monte Carlo Simulations

We demonstrate that an X-ray spectrum of a converging inflow (CI) onto a black hole is the sum of a thermal (disk) component and the convolution of some fraction of this component with the Comptonization spread (Green's) function. The latter component is seen as an extended power law at energies much higher than the characteristic energy of the soft photons. We show that the high-energy photon production (source function) in the CI atmosphere is distributed with the characteristic maximum at about the photon bending radius, 1.5rS, independently of the seed (soft) photon distribution. We show that high-frequency oscillations of the soft photon source in this region leads to the oscillations of the high-energy part of the spectrum but not of the thermal component. The high-frequency oscillations of the inner region are not significant in the thermal component of the spectrum. We further demonstrate that Doppler and recoil effects (which are responsible for the formation of the CI spectrum) are related to the hard (positive) and soft (negative) time lags between the soft and hard photon energy channels, respectively.

A New Source of Gamma Rays

Relativistic outflows or "jets" are collimated streams of high-energy electrons that emit synchrotron radiation at radio wavelengths and have bulk velocities that are a substantial fraction of the speed of light. They trace the outflow of enormous amounts of energy and matter from a central supermassive black hole in distant radio galaxies. As Fender explains in this Perspective, much smaller, more local sources may also produce such jets. Data presented by Paredes et al. point toward association of one such source, a relatively faint x-ray binary, with a gamma-ray source. This and similar pairs may contribute substantially to the production of high-energy particles and photons within our galaxy.

Semiclassical transport of particles with dynamical spectral functions

The conventional transport of particles in the on-shell quasiparticle limit is extended to particles of finite life time by means of a spectral function A(X, P,M 2) for a particle moving in an area of complex self-energy Σ ret X= Re Σ ret X−iΓ X/2 . Starting from the Kadanoff—Baym equations we derive in first-order gradient expansion equations of motion for testparticles with respect to their time evolution in X, P and M 2. The off-shell propagation is demonstrated for a couple of model cases that simulate hadron-nucleus collisions. In case of nucleus–nucleus collisions the imaginary part of the hadron self-energy Γ X is determined by the local space-time dependent collision rate dynamically. A first application is presented for A+ A reactions up to 95 A MeV, where the effects from the off-shell propagation of nucleons are discussed with respect to high energy proton spectra, high energy photon production as well as kaon yields in comparison to the available data from GANIL.

Search for the electromagnetic decay ofΔ(1232)resonance in nuclear matter

In order to inquire into the existence and significance of non-nucleonic degrees of freedom in the intermediate-energy regime, the production of protons and high-energy photons (E{sub {gamma}}{gt}30 MeV) emitted in the reaction {sup 36}Ar+{sup 27}Al at 95 MeV/nucleon has been studied. The quantitative analysis of the ({gamma}-p) invariant-mass and relative-angle distributions shows evidences of {Delta}(1232)-resonance excitation and {Delta}{r_arrow}N{gamma} decay. Experimental data are in agreement with microscopic theoretical calculations. {copyright} {ital 1998} {ital The American Physical Society}

Photon production from baryon rich quark-gluon plasma

We study high energy photon production from a quark-gluon plasma at finite baryon density. We find that the photon production spectrum from the quark-gluon plasma maintained at constant temperature is only mildly dependent on the quark chemical potential.

Neutron-proton bremsstrahlung from low-energy heavy-ion reactions.

High-energy photon yields from the reactions $^{12}\mathrm{C}$${+}^{112,124}$Sn at 10 MeV/nucleon have been measured. The ratio of cross sections (${\mathit{E}}_{\ensuremath{\gamma}}$\ensuremath{\ge}30 MeV)\ensuremath{\sigma}${(}^{124}$Sn)/\ensuremath{\sigma}${(}^{112}$Sn) is 1.6\ifmmode\pm\else\textpm\fi{}0.2, which is larger than expected within the equal-participant model. The elementary n-p-\ensuremath{\gamma} cross section is evaluated within the neutral scalar \ensuremath{\sigma} meson exchange model, and implemented into a BUU code. The results of the BUU calculation suggest that the high-energy \ensuremath{\gamma}-ray yield differences for the two Sn isotopes arise from the differences in nucelon phase-space distributions. The sensitivity of the high-energy photon production to the initial phase-space conditions is explored.

Refinements of the nucleon-exchange transport model for the emission of hard photons and nucleons.

A previously developed nucleon-exchange transport model for preequilibrium neutron and hard photon emission is extended to include proton emission. Several refinements including diffuse ground-state nucleonic momentum distributions and quantal rather than classical bremsstrahlung production are added. The incorporation of a diffuse momentum distribution improves the reproduction of experimental spectra and multiplicities, particularly at low bombarding energies. Quantal bremsstrahlung enhances the production of high-energy photons. The effect of deceleration of the colliding nuclei during the propagation of the jetting particles through the receptor nucleus is explored. The effect of preequilibrium emission on the evaporation residue and its dependence on entrance channel mass asymmetry is studied. The number of preequilibrium particles emitted is inconsistent with some previous analyses of evaporation residue spectra.

Target isotope effect in high energy photon production atE/A=10 MeV

A comparison has been made between the production of high energy (Eγ≧30 MeV)γ rays from the bombardment of124Sn and112Sn targets withE/A= 10 MeV12C ions. The results are well explained by then-p bremsstrahlung model and do not indicate the need for any new processes.

Strong impact parameter dependence of hard photon production in intermediate energy heavy ion collisions

The dependence of the high energy photon production on the impact parameter has been investigated in the reaction 129Xe+ 197Au at 44 MeV/u using the multidetector array MEDEA. A strong dependence of the high energy photon production probability on the impact parameter has been observed, while the slope parameter of the photon spectrum is almost constant. The data support the interpretation of the hard photon production in terms of first chance n-p collisions.

Erratum: Particle multiplicity dependence of high-energy photon production in a heavy-ion reaction

The production of high-energy photons in an intermediate energy heavy-ion reaction (65 MeV/nucleon $^{40}\mathrm{Ar}$${+}^{93}$Nb) is studied by characterizing the events, which produce the photons, by the forward and backward, light and heavy, charged particle production. While the absolute yield of high-energy photons increases with increasing charged particle multiplicity, the spectral shape is found to be almost independent of multiplicity. This indicates that the fundamental photon production mechanism is insensitive to the impact parameter but that the production process is more probable for the more violent collisions. This is expected for an incoherent nucleon-nucleon bremsstrahlung mechanism but not for a statistical mechanism. This work also provides a comparison of two observables that have been suggested as impact parameter selectors: the high-energy photon yield and the charged particle multiplicity. We find that the photon yield, binned by particle multiplicity, does not scale as would be expected if both techniques truly measured the impact parameter. This observation can be explained by large fluctuations in the particle multiplicity at fixed impact parameter.

Particle multiplicity dependence of high-energy photon production in a heavy-ion reaction.

The production of high-energy photons in an intermediate energy heavy-ion reaction (65 MeV/nucleon $^{40}\mathrm{Ar}$${+}^{93}$Nb) is studied by characterizing the events, which produce the photons, by the forward and backward, light and heavy, charged particle production. While the absolute yield of high-energy photons increases with increasing charged particle multiplicity, the spectral shape is found to be almost independent of multiplicity. This indicates that the fundamental photon production mechanism is insensitive to the impact parameter but that the production process is more probable for the more violent collisions. This is expected for an incoherent nucleon-nucleon bremsstrahlung mechanism but not for a statistical mechanism. This work also provides a comparison of two observables that have been suggested as impact parameter selectors: the high-energy photon yield and the charged particle multiplicity. We find that the photon yield, binned by particle multiplicity, does not scale as would be expected if both techniques truly measured the impact parameter. This observation can be explained by large fluctuations in the particle multiplicity at fixed impact parameter.