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  • SOLAR PHYSICS  (5)
  • SPACE RADIATION  (5)
  • ASTRONOMY  (1)
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  • 1
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    Compton scattering in jets: A mechanism for approximately 0.4 and less than or approximately 0.2 MeV line production (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We show that gamma-ray line emission at approximately 0.4 and less than or approximately 0.2 MeV can be produced by Compton scattering of beamed radiation in the jets of Galactic black hole candidates. This mechanism has the novel feature of not invoking the presence of e(exp +)-e(exp -) pairs. To produce the two lines, we employ a symmetric double-sided jet with bulk flow velocity of about 0.5c and incident beam radiation with a hard energy spectrum. We show that the two lines can be seen at viewing-angle cosines relative to the jet ranging from 0.2 to 0.6. This comprises 40% of the total solid angle. In addition, the line radiation is approximately 10% polarized. Depending on the bulk flow and viewing angle, the model can produce lines at other energies as well. In particular, a broad feature near 1 MeV can be seen by viewing the jet close to its axis. Our model can also accommodate single-line spectra if the beamed gamma-ray emission or the jets themselves are asymmetric.
    Keywords: SPACE RADIATION
    Type: The Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 431; 1; p. L39-L42
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  • 2
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    Secondary antiproton production in relativistic plasmas (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Angular and energy spectra of bremsstrahlung have been calculated from anisotropic electron distributions in solar flares. Results have been compared to observations of gamma-ray limb-brightening and the data on the variation of the gamma-ray spectrum with flare position on the sun.
    Keywords: SPACE RADIATION
    Type: Nature (ISSN 0028-0836); 319; 205
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  • 3
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    Pion-decay radiation and two-phase acceleration in the June 3, 1982 solar flare (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The June 3, 1982 flare is unique in the wealth of observed neutron, gamma-ray and energetic-particle emission that it produced. Using calculations of high-energy emissions to fit the various time-dependent gamma-ray fluxes, a self-consistent interaction model for the June 3 flare is constructed in which the observed fluxes are produced by two distinct particle populations with different acceleration and interaction time histories as well as different but time-independent energy spectra. The two populations are associated with first- and second-phase particle acceleration, respectively.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 6, 19
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  • 4
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    Directionality of bremsstrahlung from relativistic electrons in solar flares (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Angular and energy spectra of bremsstrahlung have been calculated from anisotropic electron distributions in solar flares. Results have been compared to observations of gamma-ray limb-brightening and to data on the variation of the gamma-ray spectrum with flare position on the sun.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 301; 962-974
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  • 5
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    Neutron and antineutron production in accretion onto compact objects (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Nuclear reactions in the hot accretion plasma surrounding a collapsed star are a source of neutrons, primarily through spallation and pion-producing reactions, and antineutrons, principally through the reaction p+p yields p+p+n+anti-n. We calculate spectra of neutrons and antineutrons produced by a variety of nonthermal energetic particle distributions in which the target particles are either at rest or in motion. If only neutral particles are free to escape the interaction site, a component of the proton and antiproton fluxes in the cosmic radiation results from the neutrons and antineutrons which leave the accretion plasma and subsequently decay in the interstellar medium. This additional antiproton component could account for the enhanced flux of antiprotons in the cosmic radiation, compared to values expected from the standard leaky-box model of cosmic-ray propagation and confinement. Moreover, the low-energy antiproton flux measured by Buffington et al. (1981) could result from target-particle motion in the accretion plasma. This model for the origin of antiprotons predicts a narrow 2.223 MeV line which could be observable.
    Keywords: SPACE RADIATION
    Type: NASA-TM-89264 , NAS 1.15:89264
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  • 6
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    Directionality of bremsstrahlung from relativistic electrons in solar flares (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Angular and energy spectra of bremsstrahlung have been calculated from anisotropic electron distributions in solar flares. Results have been compared to observations of gamma-ray limb-brightening and to data on the variation of the gamma-ray spectrum with flare position on the sun.
    Keywords: SOLAR PHYSICS
    Type: NASA-TM-87509 , NAS 1.15:87509
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  • 7
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    Secondary antiproton production in relativistic plasmas (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The possibility is investigated that the reported excess low energy antiproton component of the cosmic radiation results from proton-proton (p-p) interactions in relativistic plasmas. Because of both target and projectile motion in such plasmas, the antiproton production threshold in the frame of the plasma is much lower than the threshold of antiproton production in cosmic ray interactions with ambient matter. The spectrum of the resultant antiprotons therefore extends to much lower energy than in the cosmic ray case. The antiproton spectrum is calculated for relativistic thermal plasmas and the spectrum is estimated for relativistic nonthermal plasmas. As possible production sites, matter accreting onto compact objects located in the galaxy is considered. Possible overproduction of gamma rays from associated neutral pion production can be avoided if the site is optically thick to the photons but not to the antiprotons. A possible scenario involves a sufficiently large photon density that the neutral pion gamma rays are absorbed by photon-photon pair production. Escape of the antiprotons to the interstellar medium can be mediated by antineutron production.
    Keywords: SPACE RADIATION
    Type: OG-6.1-4 , 19th Intern. Cosmic Ray Conf - Vol. 2; p 338-341; NASA-CP-2376-VOL-2
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  • 8
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    High-energy gamma radiation from extragalactic radio sources (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We propose that the important relationship between 3C 273 and 3C 279, the first two extragalactic sources detected at over 100 MeV energies, is their superluminal nature. In support of this conjecture, we propose a kinematic focusing mechanism, based on Compton scattering of accretion-disk photons by relativistic nonthermal electrons in the jet, that preferentially emits gamma rays in the superluminal direction.
    Keywords: SPACE RADIATION
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 256; 2; p. L27-L30.
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  • 9
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    OSSE observations of 3C 273 (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: We report results of multiple observations of the quasar 3C 273 with the Oriented Scintillation Spectrometer Experiment (OSSE) instrument on the Compton Gamma Ray Observatory. These observations span the period from 1991 June through 1993 January and represent the most sensitive observations to date in low-energy gamma rays. The source was detected at historically weak 100 keV fluxes compared with previous measurements. Variability by factors of approximately 3 on timescales of approximately equal 2 months was observed in the energy band 50-150 keV. The data are well described by a single power law with a proton number index Gamma = 1.7 +/- 0.1. No significant change of Gamma was observed during changes in intensity. Thermal models do not provide acceptable fits to the data. When the OSSE data are combined with contemporaneous measurements by COMPTEL and EGRET, the spectrum is seen to break at an energy of 1.0(+0.9, -0.4) MeV to a softer power law with Delta Gamma = 0.7(+0.06, -0.11), forming a power law with Gamma = 2.4 between approximately 1 MeV and several GeV.
    Keywords: ASTRONOMY
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 1; p. 182-188
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  • 10
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    High-energy processes in solar flares (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A detailed study of high-energy processes in solar flares is reported, including the production of neutrons and pions, and incorporating isobaric and scaling models and a recent compilation of pion production data (Dermer, 1986). The broad-band gamma-ray spectrum resulting from the decay of neutral pions, the bremsstrahlung of positrons and electrons from the decay of charged pions, and the annihilation in flight of positrons is evaluated. Also evaluated is the 0.511 MeV gamma-ray line resulting from the annihilation of the positrons which survive annihilation in flight. Calculations were based on an isotropic, thick-target model using the best available nuclear data and models. Results are compared with extensive observation of the June 3, 1982 flare (10-120 MeV gamma rays), 0.511 and 2.2 MeV line emission, nuclear line emission, high-energy neutrons, and interplanetary charged particles.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 63; 721-748
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