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1.
We review the recent developments of laser pair creation in the laboratory and their potential applications to astrophysics and other frontiers. Many astrophysical phenomena involving e+e− plasmas may be systematically investigated in the laboratory setting. We also discuss potential applications of dense positronium gas.  相似文献   

2.
If massive sterile neutrinos exist, their decays into photons and/or electron-positron pairs may give rise to observable consequences. We consider the possibility that MeV sterile neutrino decays lead to the diffuse positron annihilation line in the Milky Way center, and we thus obtain bounds on the sterile neutrino decay rate Γ e ≥10−28 s−1 from relevant astrophysical/cosmological data. Also, we expect a soft gamma flux of 1.2×10−4–9.7×10−4 ph cm−2 s−1 from the Milky Way center which shows up as a small MeV bump in the background photon spectrum. Furthermore, we estimate the flux of active neutrinos produced by sterile neutrino decays to be 0.02–0.1 cm−2 s−1 passing through the earth.  相似文献   

3.
We present the results of experiments in which jets are created through the collision of two laser-produced plasmas. These experiments use a simple ‘v-foil’ target design: two thin foils are placed at an angle of 140° to each other, and irradiated with a high-energy laser. The plasmas from the rear face of these foils collide and drive plasma jets moving with a velocity of ～300 km?s?1. By choosing the foil thickness and material to suit the laser conditions available, it has proven possible to create plasma jets for which the relevant scaling parameters show significant overlap with those of outflows associated with young stellar objects (YSOs). Preliminary results are also shown from experiments to study the effect of an ambient gas on jet propagation. Nominally identical experiments are conducted either in vacuum or in an ambient medium of 5 mbar of nitrogen gas. The gas is seen to increase the jet collimation, and to introduce shock structures at the head of the outflow.  相似文献   

4.
A finite amplitude linearly polarized electromagnetic wave propagating in a relativistic plasma, is found to generate the longitudinal d.c. as well as the oscillating electric field at the second harmonic. In a plasma consisting of only electrons and positrons, these fields cannot be generated.The evolution of the electromagnetic waves is governed by the non-linear Schrödinger equation which shows that the electromagnetic solitons are always possible in ultra-relativistic plasmas (electron-ion or electron-positron) but in a plasma with relativistic electrons and nonrelativistic ions, these solitons exist only if 1(KT e/meC2)<(2m i/15me);m e andm i being the electron and ion mass andT e the electron temperature. Both the d.c. electric field and the solitons provide a nonlinear mechanism for anomalous acceleration of the particles. This model has direct relevance to some plasma processes occurring in pulsars.  相似文献   

5.
We have applied numerical simulations and modeling to the particle acceleration, magnetic field generation, and emission from relativistic shocks. We investigate the nonlinear stage of theWeibel instability and compare our simulations with the observed gamma-ray burst emission. In collisionless shocks, plasma waves and their associated instabilities (e.g., the Weibel, Buneman and other two-stream instabilities) are responsible for particle (electron, positron, and ion) acceleration and magnetic field generation. 3-D relativistic electromagnetic particle (REMP) simulations with three different electron-positron jet velocity distributions and also with an electron-ion plasma have been performed and show shock processes including spatial and temporal evolution of shocks in unmagnetized ambient plasmas. The growth time and nonlinear saturation levels depend on the initial jet parallel velocity distributions. Simulations show that the Weibel instability created in the collisionless shocks accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The nonlinear fluctuation amplitude of densities, currents, electric, and magnetic fields in the electron-positron shocks are larger for smaller jet Lorentz factor. This comes from the fact that the growth time of the Weibel instability is proportional to the square of the jet Lorentz factor. We have performed simulations with broad Lorentz factor distribution of jet electrons and positrons, which is assumed to be created by photon annihilation. Simulation results with this broad distribution show that the Weibel instability is excited continuously by the wide-range of jet Lorentz factor from lower to higher values. In all simulations the Weibel instability is responsible for generating and amplifying magnetic fields perpendicular to the jet propagation direction, and contributes to the electron’s (positron’s) transverse deflection behind the jet head. This small scale magnetic field structure contributes to the generation of “jitter” radiation from deflected electrons (positrons), which is different from synchrotron radiation in uniform magnetic fields. The jitter radiation resulting from small scale magnetic field structures may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks. The detailed studies of shock microscopic process evolution may provide some insights into early and later GRB afterglows.  相似文献   

6.
It is shown that some aspects of the accretion disc physics can be experimentally simulated with the use of an array of properly directed plasma jets created by intense laser beams. For the laser energy of 1 to 3 kJ, one can create a quasi-planar disc with the Reynolds number exceeding 104 and magnetic Reynolds number in the range of 10–100. The way of seeding the disc with the magnetic field by using a cusp magnetic configuration is described.  相似文献   

7.
A recent measurement of thee +/(e ++e –) ratio in cosmic rays between 5 and 50 GeV (HEAT experiment), is consistent with positron production theories via primary cosmic radiation interactions in the interstellar medium. This paper will show that atmospheric corrections result in a 50% level of uncertainty in thee +/(e ++e –) ratio measurements carried out with balloon-borne experiments. In light of the current theories on electron-positron production in neutron stars and by using different calculations for atmospheric corrections, a lower limit on Milky Way pulsar birthrate of 30–60 years can be set on the basis of recent observations of the positron fraction in cosmic rays.  相似文献   

8.
The nonlinear ion-acoustic double layers (IADLs) in a warm magnetoplasma with positive-negative ions and nonthermal electrons are investigated. For this purpose, the hydrodynamic equations for the positive-negative ions, nonthermal electron density distribution, and the Poisson equation are used to derive a modified Zakharov–Kuznetsov (MZK) equation, in the small amplitude regime. It is found that compressive and rarefactive IADLs strongly depend on the mass and density ratios of the negative-to-positive ions as well as the nonthermal electron parameter. Also, it is shown that there are one critical value for the density ratio of the negative-to-positive ions (ν), the ratio between unperturbed electron-to-positive ion density (μ), and the nonthermal electron parameter (β), which decide the existence of positive and negative IADLs. The present study is applied to examine the small amplitude nonlinear IADL excitations for the (H+, O2-)(\mathrm{H}^{+}, \mathrm{O}_{2}^{-}) and (H+,H−) plasmas, where they are found in the D- and F-regions of the Earth’s ionosphere. This investigation should be helpful in understanding the salient features of the nonlinear IADLs in either space or laboratory plasmas where two distinct groups of ions and non-Boltzmann distributed electrons are present.  相似文献   

9.
E × B-drifting jets have been generally ignored for the past 25 years even though they may well describe all the astrophysical jet sources, both on galactic and stellar scales. Here we present closed-form solutions for their joint field-and-particle distribution, argue that the observed jets are near equipartition, with extremely relativistic, monoenergetic e±-pairs of bulk Lorentz factor γ ≲ 104, and are first-order stable. We describe plausible mechanisms for the jets’ (i) formation, (ii) propagation, and (iii) termination. Wherever a beam meets with resistance, its frozen-in Poynting flux transforms the delta-shaped energy distribution of the pairs into an almost white power law,E 2 N E ∼E −∫ with ∫ ≳ 0, via single-step falls through the huge convected potential.  相似文献   

10.
Irradiating high-Z targets such as gold with ultra-intense lasers creates electron-positron pairs. In particular, the positron density in the plasma created by this procedure is higher than that obtained via other laboratory-based methods, with theoretical maximum densities exceeding 1018 cm−3. All of the significantly contributing processes are well-known and hence we can study this phenomenon using Monte Carlo simulation. We focus on the latter part of this procedure, the passage of high-energy electrons through the target creating pairs. In particular, we discuss the usefulness of CERN’s GEANT4 Monte Carlo code in simulating this process. Once this code is successfully calibrated, we will use it to perform parameter studies, and design future targets to optimize the positron yield.  相似文献   

11.
Questions of the equilibrium, stability, and observational manifestations of strange stars are considered, in which electrical neutralization of the quark matter is provided by positrons, as occurs for some sets of bag parameters resulting in a stiffer equation of state. Such models consist entirely of self-contained, strange quark matter and their maximum mass reaches 2.4–2.5 M⊙ with a radius of 13–14 km. The cooling of such strange quark stars both in the absence and in the presence of mass accretion is investigated. It is shown that in the absence of mass accretion onto the strange star, the dependence of temperature (T, K) on age (t, yr) depends very little on the mass of the configuration and has the form T ≈ 2.3·108r−1/5. If the star’s initial temperature is sufficiently high (T0≥2·1010K), then the total number of electron-positron pairs emitted does not depend on it and is determined only by the total mass of the configuration. In the case of accretion, the annihilation of electrons of the infalling fatter with positrons of the strange quark matter results in the emission of γ-rays with an energy of∼0.5 MeV, by observing which one can distinguish candidates for strange stars. The maximum temperature of strange stars with mass accretion is calculated. Translated from Astrofizika, Vol. 42, No. 4, pp. 617–630, October–December, 1999.  相似文献   

12.
A brief summary is presented of requirements for the measurements of extragalactic γ-ray lines. The electron-positron annihilation line at 511 keV represents the best prospect, and although this line is greatly broadened in active galactic nuclei, a narrow line should be present in clusters of galaxies and radio lobes as a result of prior AGN activity. The strongest fluxes should be of the order of 10−4 photons cm−2 s−1 from the closest extended sources.  相似文献   

13.
Based on our spectroscopic observations of the variable planetary nebula IC 4997 in 2003–2009, we have obtained the relative fluxes in optical emission lines. The interstellar extinction c = 0.35 has been found from the Balmer decrement by taking into account the effect of self-absorption in hydrogen lines in dense nebular regions. The variations in the Balmer decrement point to variability of the self-absorption and circumstellar extinction. We have investigated the variations in the relative intensities of some spectral lines and their ratios with time. The drop in the ratios F(λ4363)/F(Hγ) and F(λ363)/F(λ4959) that began back in 1990–1995 has continued, suggesting a decrease in the electron density and temperature in the central nebular region. The ratio F(λ6731)/F(λ6717) has remained constant. It gives an estimate for the electron density in the outer regions of IC 4997, N e ∼ 104 cm−3.  相似文献   

14.
I summarize here recent work on the physical conditions in blazar jets including the comparison between emission regions at subparsec scales (1016−17 cm) and at very large scales (1022−24 cm) recently detected in X-rays by Chandra. The jet properties at both scales together with those of the presumed associated accretion disk (1014−15 cm) suggest the possibility of a unified scenario for the origin and propagation of jets in strong radio sources.  相似文献   

15.
We analyzed the feedback of AGN jets on cooling flow clusters using three-dimensional AMR hydrodynamic simulations. We studied the interaction of the jet with the intracluster medium and creation of low X-ray emission cavities (Bubbles) in cluster plasma. The distribution of energy input by the jet into the system was quantified in its different forms, i.e. internal, kinetic and potential. We find that the energy associated with the bubbles, (pV+γ pV/(γ−1)), accounts for less than 10 percent of the jet energy.  相似文献   

16.
We describe experiments that investigate the capability of an experimental platform, based on laser-driven blast waves created in a medium of atomic clusters, to produce results that can be scaled to astrophysical situations. Quantitative electron density profiles were obtained for blast waves produced in hydrogen, argon, krypton and xenon through the interaction of a high intensity (I ≈ 1017 Wcm−2), sub-ps laser pulse. From this we estimate the local post-shock temperature, compressibility, shock strength and adiabatic index for each gas. Direct comparisons between blast wave structures for consistent relative gas densities were achieved through careful gas jet parameter control. From these we investigate the applicability of different radiative and Sedov-Taylor self-similar solutions, and therefore the (ρ,T) phase space that we can currently access.  相似文献   

17.
A double-pulse laser drive is used to create episodic supersonic plasma jets that propagate into a low density ambient medium. These are among the first laser experiments to generate pulsed outflow. The temporal laser-intensity profile consists of two 1-ns square pulses separated by 9.6 ns. The laser is focused on a truncated conical plug made of medium Z material inserted into a high-Z washer. Unloading material from the plug is collimated within the cylindrical washer hole, then propagates into the low-Z foam medium. The resulting jet is denser than the ambient medium. Double-pulse jet evolution is compared to that driven by a single laser pulse. The total drive energy is the same for both jets, as if a source with fixed energy generated a jet from either one or two bursts. Radiographs taken at 100 ns show that a single-pulse jet was broader than the double-pulse jet, as predicted by hydrodynamic simulations. Since the initial shock creating the jet is stronger when all the energy arrives in a single pulse, the jet material impacts the ambient medium with higher initial velocity. Detailed comparisons between single- and double-pulsed jet rheology and shock structure are presented. 2-D hydrodynamic simulations are compared to the experimental radiographs. PACS: 52.30.−q 41.75.Jv 42.62.−b 42.68.Sq 47.40.−x 47.56.+r  相似文献   

18.
The Franck-Condon factors and r-centroids, which are very closely related to vibrational transition probabilities, have been evaluated by the more reliable numerical integration procedure for the bands of B 2∑+ − X 2∑+, F 2∑+ − X 2∑+ systems of SrF and C 1∑+ − X 1∑+, G 1Π − X 1∑+ systems of ScF molecules of astrophysical interest, using a suitable potential.  相似文献   

19.
In weakly ionized astrophysical plasmas, shear flow induced plasma - neutral gas friction yields self-generated magnetic fields of seed-field order. This process is of cosmological importance and relevant for protogalactic systems like Lyα-clouds. In our contribution we illustrate this mechanism by the help of 3-dimensional 2-fluid simulations of primordial rotating gas clumps in Lyα-clouds showing that plasma - neutral gas interactions cause large scale magnetic fields of the order of 10−15G on time scales of the order of 106yrs. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

20.
Starting from appropriate fluid equations, a dispersion relation describing the properties of low frequency (as compared to the ion gyrofrequency) shear electromagnetic mode in an ultra-dense, relativistic-degenerate plasma is derived and examined. The plasma constituents are fully degenerate electrons and positrons, and strongly correlated non-degenerate ions. It is found that the shear mode can couple with the electrostatic ion mode under certain circumstances. The electron and positron relativistic degeneracy and ion correlations significantly affect the waves. However, the electron degeneracy pressure is dominant because the density balance changes due to the presence of ions in electron-positron pair plasma. The results are discussed numerically in the ultra-relativistic and weakly-relativistic limits, indicating relevance to the dense plasmas, produced in laboratory (e.g., super-intense laser-dense matter experiments), and astrophysical regimes.  相似文献   

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