A role of cosmic rays in generation of radio and optical radiation by plasma mechanisms
01 Apr 1987-Astrophysics and Space Science (Kluwer Academic Publishers)-Vol. 132, Iss: 2, pp 213-248
TL;DR: In this article, the authors examined the radiation of ultrarelativistic particles in a quasi-uniform magnetic field superimposed by a wide spectrum of magnetic, electric, and electron density inhomogeneities created in a turbulent plasma.
Abstract: The radiation of ultrarelativistic particles is examined in a quasi-uniform magnetic field superimposed by a wide spectrum of magnetic, electric, and electron density inhomogeneities created in a turbulent plasma. The radiation spectrum from a particle of a given energy is shown to acquire a high-frequency power-law tail with the same spectral index as the index ν of small-scale turbulence. For a power-law spectrum of ultrarelativistic electrons, dN(ℰ)/dℰ ~ ℰ−ξ, with a cut-off at some energy ℰmax, the radiation spectrum consists of a few power-law ranges; the radiation intensity may suffer jumps at frequencies which separate these ranges. In the high-frequency range the spectral index ν is determined by small-scale magnetic and electric fields. At intermediate frequencies the main contribution comes from the synchrotron radiation in a large-scale field; the radiation spectrum has an index α=(ζ−1)/2. The same index may be produced by large-scale Langmuir waves. At lower frequencies the radiation spectrum increases owing to the transition radiation caused by electron density fluctuations; in this case the spectral index is equal to ζ+1−ν. The possibility of diagnostics of high-frequency cosmic plasma turbulence from radiation of high-energy particles is discussed. It is shown that the proposed theory may explain some features in the spectra of several cosmic objects.
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TL;DR: In this paper, the radiative signature of the first-order Fermi acceleration mechanism for gamma-ray bursts was studied. And the authors showed that this upper bound on both the electron Lorentz factor and on the energy of the photons radiated during the scattering process can be found in the model of relativistic, weakly magnetized collisionless shocks.
Abstract: Particle-in-cell simulations of relativistic, weakly magnetized collisionless shocks show that particles can gain energy by repeatedly crossing the shock front. This requires scattering off self-generated small length-scale magnetic fluctuations. The radiative signature of this first-order Fermi acceleration mechanism is important for models of both the prompt and afterglow emission in gamma-ray bursts and depends on the strength parameter a = {lambda}e|{delta}B|/mc {sup 2} of the fluctuations ({lambda} is the length scale and |{delta}B| is the magnitude of the fluctuations). For electrons (and positrons), acceleration saturates when the radiative losses produced by the scattering cannot be compensated by the energy gained on crossing the shock. We show that this sets an upper limit on both the electron Lorentz factor and on the energy of the photons radiated during the scattering process. This rules out jitter radiation on self-excited fluctuations with a 1, radiation is generated by the standard synchrotron mechanism, and the maximum photon energy rises linearly with a, until saturating at 70 MeV, when a =more » a {sub crit}.« less
92 citations
Cites background from "A role of cosmic rays in generation..."
...The spectrum of photons that are emitted when a particle is scattered by turbulent fluctuations is, in the general case, quite complex (Toptygin & Fleishman 1987)....
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01 Jan 1963
TL;DR: The observed isotropy of the cosmic rays incident on the earth is claimed to be a consequence of a magnetic field assumed to exist in interstellar space, which is compared with the average interstellar field of 10−20 gauss.
Abstract: IT is important to decide whether or not the main sources of the cosmic ray particles are external to our galaxy. An external source seems, at first sight, to be established by the observed isotropy of the cosmic rays incident on the earth. But it has been claimed by a number of authors that this isotropy is simply a consequence of a magnetic field assumed to exist in interstellar space. The basis for this claim is that a single particle of energy η and charge e is deflected through an appreciable angle after travelling a distance d across a magnetic field of intensity H, provided For η equal to 1010 eV., e equal to the electronic charge (4.77 × 10−10 E.S.U.), and d equal to the radius of the galaxy (∼ 3 × 1022 cm.), the necessary value of H is about 10−15 gauss. This value may be compared with the average interstellar field of about 10−20 gauss that would result if (i) every star possessed a magnetic moment equal to the commonly quoted magnetic moment for the sun (∼ 1.5 × 1034 C.G.S.); (ii) the stellar magnetic dipoles were all aligned parallel to each other.
62 citations
TL;DR: In this article, the authors consider the synchrotron emission from relativistic shocks assuming that the radiating electrons cool rapidly (either through synchoretron or any other radiation mechanism).
Abstract: We consider the synchrotron emission from relativistic shocks assuming that the radiating electrons cool rapidly (either through synchrotron or any other radiation mechanism). It is shown that the theory of synchrotron emission in the fast cooling regime can account for a wide range of spectral shapes. In particular, the magnetic field, which decays behind the shock front, brings enough flexibility to the theory to explain the majority of gamma-ray burst spectra even in the parameter-free fast cooling regime. Also, we discuss whether location of the peak in observed spectral energy distributions of gamma-ray bursts and active galactic nuclei can be made consistent with predictions of diffusive shock acceleration theory, and find that the answer is negative. This result is a strong indication that a particle injection mechanism, other than the standard shock acceleration, works in relativistic shocks.
54 citations
TL;DR: In this paper, the spectrum of electromagnetic emission generated by relativistic electrons scattered on small-scale random magnetic fields, implied by current models of the magnetic field generation in the gamma-ray burst sources, is considered.
Abstract: The spectrum of electromagnetic emission generated by relativistic electrons scattered on small-scale random magnetic fields, implied by current models of the magnetic field generation in the gamma-ray burst sources, is considered. The theory developed includes both perturbative and nonperturbative versions and therefore suggests a general treatment of the radiation in an arbitrary small-scale random field. It is shown that a general treatment of the random nature of the small-scale magnetic field, as well as angular diffusion of the electrons due to multiple scattering by magnetic inhomogeneities (i.e., nonperturbative effects), gives rise to a radiation spectrum that differs significantly from the so-called "jitter" spectrum. The spectrum of diffusive synchrotron radiation seems to be consistent with the low-energy spectral index distribution of the gamma-ray bursts.
54 citations
Cites background or methods from "A role of cosmic rays in generation..."
...2 presents radiation spectra (calculated with the use of the non-perturbative formulae (35) of (Toptygin & Fleishman 1987a), or, equivalently, Eq....
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...The non-perturbative version of the theory is not discussed in any detail here since it is published elsewhere (Toptygin & Fleishman 1987a,b; Toptygin et al. 1987; Fleishman 2006)....
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...(35) of (Toptygin & Fleishman 1987a)....
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...The full non-perturbative theory was later worked out by Toptygin & Fleishman (1987a); Toptygin et al. (1987), allowing in particular net deflections of the radiating particles that are not necessarily small (e.g., by a large-scale magnetic field and/or multiple scattering on small-scale…...
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TL;DR: In this paper, an alternative method that uses the concept of the photon formation length is presented. But it is not suitable for evaluating spectra both from particles moving in a specific realization of a turbulent electromagnetic field or from trajectories given as a finite, discrete time series by a particle-in-cell simulation.
Abstract: Particle-in-cell (PIC) simulations of relativistic shocks are in principle capable of predicting the spectra of photons that are radiated incoherently by the accelerated particles. The most direct method evaluates the spectrum using the fields given by the Lienard-Wiechart potentials. However, for relativistic particles this procedure is computationally expensive. Here we present an alternative method that uses the concept of the photon formation length. The algorithm is suitable for evaluating spectra both from particles moving in a specific realization of a turbulent electromagnetic field or from trajectories given as a finite, discrete time series by a PIC simulation. The main advantage of the method is that it identifies the intrinsic spectral features and filters out those that are artifacts of the limited time resolution and finite duration of input trajectories.
52 citations
Cites background from "A role of cosmic rays in generation..."
...Turbulent fields In a turbulent magnetic field, the particle trajectory and resulting radiation spectrum are generally quite complex (Toptygin & Fleishman 1987)....
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...…1956) — a well-studied phenomenon in the context of the sup- pression of bremsstrahlung and pair-production in crystals and other media (for a review see Klein 1999), though not usually considered in the context of synchrotron radiation (although see Toptygin & Fleishman 1987; Fleishman 2006b)....
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References
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Book•
01 Jan 1960
TL;DR: In this article, the propagation of electromagnetic waves and X-ray diffraction of X rays in crystals are discussed. But they do not consider the effects of superconductivity on superconducting conductors.
Abstract: Electrostatics of conductors Static magnetic field Superconductivity The propagation of electromagnetic waves Spatial dispersion Diffraction of X rays in crystals.
12,543 citations
TL;DR: In this paper, it was claimed that the observed isotropy of the cosmic rays incident on the earth is simply a consequence of a magnetic field assumed to exist in interstellar space, and the basis for this claim is that a single particle of energy n and charge e is deflected through an appreciable angle after travelling a distance d across a magnetic magnetic field of intensity H, provided n equal to 1010 eV., e equal to the electronic charge (4·77 × 10-10 E.G.U.), and d equal to radius of the galaxy (∽3
Abstract: IT is important to decide whether or not the main sources of the cosmic ray particles are external to our galaxy. An external source seems, at first sight, to be established by the observed isotropy of the cosmic rays incident on the earth. But it has been claimed by a number of authors that this isotropy is simply a consequence of a magnetic field assumed to exist in interstellar space. The basis for this claim is that a single particle of energy n and charge e is deflected through an appreciable angle after travelling a distance d across a magnetic field of intensity H, provided For n equal to 1010 eV., e equal to the electronic charge (4·77 × 10-10 E.S.U.), and d equal to the radius of the galaxy (∽3 × 1022 cm.), the necessary value of H is about 10-15 gauss. This value may be compared with the average interstellar field of about 10-20 gauss that would result if (i) every star possessed a magnetic moment equal to the commonly quoted magnetic moment for the sun (∽ 1·5 × 1034 C.G.S.) ; (ii) the stellar magnetic dipoles were all aligned parallel to each other.
749 citations
Book•
01 Jan 1990TL;DR: In this paper, the authors discuss transition radiation and transition scattering in the context of transition bremsstrahlung radiation and the corresponding range of phenomena, as far as possible, in a generally physical aspect.
Abstract: Transition radiation is a process of a rather general character. It occurs when some source, which does not have a proper frequency (for example, a charge) moves at a constant velocity in an inhomogeneous and (or) nonstationary medium or near such a medium. The simplest type of transition radiation takes place when a charge crosses a boundary between two media (the role of one of the media may be played by vacuum). In the case of periodic variation of the medium, transition radiation possesses some specific features (resonance transition radiation or transition scattering). Transition scattering occurs, in particular, when a permittivity wave falls onto an nonmoving (fixed) charge. Transition scattering is closely connected with transition bremsstrahlung radiation. All these transition processes are essential for plasma physics. Transition radiation and transition scattering have analogues outside the framework of electrodynamics (like in the case of Vavilov?Cherenkov radiation). In the present report the corresponding range of phenomena is elucidated, as far as possible, in a generally physical aspect.
348 citations