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  • SPACE RADIATION  (5)
  • 1
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    Cyclotron scattering lines in gamma-ray burst spectra (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: If cyclotron scattering, rather than absorption, is responsible for the line features observed recently in two gamma-ray burst spectra (Murakami et al., 1988), then the second and higher harmonics are due to resonant scattering events that excite the electron to Landau levels above the ground state. Here, relativistic Compton scattering cross sections are used to estimate the expected ratio of third to second harmonics in the presence of Doppler broadening. At the field strength (1.7 TG) required to give first and second harmonics at 19 keV and 38 keV, there should be no detectable third harmonic in the spectrum.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 338; L21-L24
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  • 2
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    Cyclotron resonant scattering and absorption (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The relativistic cross-sections for first-order absorption and second-order scattering are compared to determine the conditions under which the absorption cross-section is a good approximation to the much more complex scattering cross-section for purposes of modeling cyclotron lines in gamma-ray bursts. Differences in both the cross-sections and the line profiles are presented for a range of field strengths, angles, and electron temperatures. The relative difference of the cross-sections at one line width from resonance was found to increase with field strength and harmonic number. The difference is also strongly dependent on the photon angle to the magnetic field. For the field strength, 1.7 x 10 to the 12th G, and the angle inferred from the Ginga burst features, absorption is an excellent approximation for the profiles at the first and second harmonics.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 374; 687-699
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  • 3
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    Positron annihilation in gamma-ray bursts (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Emission features appear at energies of 350 to 450 keV in the spectra of a number of gamma ray burst sources. These features were interpreted as electron-positron annihilation lines, redshifted by the gravitational field near the surface of a neutron star. Evidence that gamma ray bursts originate at neutron stars with magnetic field strengths of approx. 10(exp 12) Gauss came from recent observations of cyclotron scattering harmonics in the spectra of two bursts. Positrons could be produced in gamma ray burst sources either by photon-photon pair production or by one-photon pair production in a strong magnetic field. The annihilation of positrons is affected by the presence of a strong neutron star magnetic field in several ways. The relaxation of transverse momentum conservation causes an intrinsic broadening of the two-photon annihilation line and there is a decrease in the annihilation cross section below the free-space value. An additional channel for one-photon annihilation also becomes possible in high magnetic fields. The physics of pair production and annihilation near strongly magnetized neutron stars will be reviewed. Results from a self-consistent model for non-thermal synchrotron radiation and pair annihilation are beginning to identify the conditions required to produce observable annihilation features from strongly magnetized plasmas.
    Keywords: SPACE RADIATION
    Type: Annihilation in Gases and Galaxies; p 169-183
    Format: application/pdf
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  • 4
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    Comptonization of thermal photons by relativistic electron beams (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper presents a numerical calculation of gamma-ray emission produced by Compton scattering of relativistic electron beams on background thermal radiation, which includes spatial dependence of electron energy losses and cyclotron resonance scattering in a strong magnetic field. In the first version, the scattering is described by the fully relativistic Klein-Nishina cross section, but the magnetic field is neglected. In the second version, the scattering is described by the magnetic resonant cross section in the Thomson limit. It is found that when the magnetic field is not included, electron energy losses are important only at higher neutron star surface temperatures (T about 3,000,000 K). In the presence of a strong magnetic field, (10 to the 12th G), resonant scattering greatly increases electron energy losses, making scattering very efficient even at lower surface temperatures. Resulting photon and electron spectra for both cases ae discussed in relation to models for pulsar X-ray and gamma-ray emission.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 336; 861-874
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  • 5
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    The pulsar contribution to galactic cosmic ray positrons (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Measurements of high energy positrons in the cosmic rays appear to show an increase in the positron fraction above 10 GeV which is inconsistent with theoretical predictions of secondary positron production. We explore the possibility that observations of .1 - 1 GeV and very high energy (VHE) gamma-rays from the Crab and Vela pulsars could imply a significant primary positron contribution from galactic radio pulsars at energies above 10 GeV. Assuming that positrons are produced through magnetic pair creation in the cascades near the polar cap which may be the source of the observed gamma rays, we can estimate the flux and spectrum of the pulsar positron contribution. The pulsar positron component has a flatter spectrum than that expected from secondary cosmic ray production. The level of this contribution above 10 GeV is high enough to make pulsars viable sources of the high energy positron excess, and may also put interesting constraints on pulsar emission models.
    Keywords: SPACE RADIATION
    Type: SESSION-OG-6.2-2 , Laboratory for High Energy Astrophysics Contributions to the 20th International Cosmic Ray Conference; 4 p
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