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  • 1
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    Diffusive electron acceleration at SNR shock fronts and the observed SNR radio spectral indices (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The radio synchrotron emission from relativistic electrons in shell supernova remnants (SNRs) provides a unique opportunity to probe the energy distribution of energetic electrons at their acceleration site (SNR shock fronts). This information provides insight into the acceleration mechanism(s). The implications of these observations for the diffusive (first-order Fermi) acceleration of electrons at the SNR shock fronts are discussed.
    Keywords: SPACE RADIATION
    Type: NASA. Goddard Space Flight Center Nineteenth International Cosmic Ray Conference. Conference Papers: Invited Rapporteur, Highlight, Miscellaneous, Volume 9; 4 p
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  • 2
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    On the anomalous component (1985)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The so-called anomalous cosmic ray component, which occurs at energies of about 10 MeV/nucleon and consists only of He, N, O, and Ne, has been a subject of interest for more than a decade. The origin of this component is generally considered to be interstellar neutral gas that is ionized and accelerated in the solar wind. The mechanism and the location for the acceleration, however, remains an unsolved problem. A model is used which includes the effects of gradient and curvature drifts and considers the implications of observed spatial gradients of the anomalous component for the location of the acceleration region. It is concluded that if drifts are important the acceleration region cannot lie at the solar poles. It is also concluded that there is no single region for the acceleration which can account for both the observed intensities and gradients in models which include drift effects.
    Keywords: SPACE RADIATION
    Type: SH-4.6-6 , 19th Intern. Cosmic Ray Conf - Vol. 5; p 180-183; NASA-CP-2376-VOL-5
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  • 3
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    A simple model for the formation of 'reflected', 'intermediate', and 'diffuse' ion distributions upstream of earth's bow shock (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Detailed energetic ion and low-frequency wave experiments on ISEE 1, 2, and 3, have established correlations between the types of ion populations and waves observed to exist in the earth's foreshock region. The present calculation has the objective to quantitatively test the picture obtained for the earth's foreshock region. An analysis is conducted of the coupled spatial and temporal evolution of upstream protons and hydromagnetic waves by means of a simple model in which the protons are represented by counterstreaming beams which resonate with hydromagnetic waves, exciting the outward propagating modes and damping the inward propagating modes at a single wave number.
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 39-45
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  • 4
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    Hydromagnetic waves and cosmic-ray diffusion theory (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Pitch-angle (and energy) diffusion of cosmic rays in hydromagnetic wave fields is considered. The treatment remains strictly within the quasi-linear approximation. It is shown that the popular assumption of an isotropic power spectrum tensor of magnetic fluctuations requires in this case equal forms and magnitudes of Alfven and magnetosonic wave spectra - a situation which is generally unlikely. The relative contributions to the pitch-angle diffusion coefficient from the cyclotron resonances and Landau resonance due to the different types of waves are evaluated for a typical situation in the solar wind. Since the Landau resonance in this approximation also does not lead to particle reflections, a proper consideration of the nonlinear particle orbits is indeed necessary to overcome the well-known difficulties of quasi-linear scattering theory for cosmic rays near 90 deg pitch angle.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal; 198; June 1
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  • 5
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    Temporal development of diffuse ion events upstream of the earth's bow shock - The October 31, 1977, event (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The origin of the intensity-time profile characteristic of diffuse ion events upstream of the earth's bow shock is investigated. It is believed that the profile results from a rotation of the interplanetary magnetic field that produces as a systematic variation in the connection time of field lines with the bow shock. If the connection time exceeds the time needed to reach equilibrium between the shock acceleration and ion loss processes, a plateau in the ion intensity is formed. The upstream diffusion ion event of October 31, 1977, for which simultaneous magnetic field and ion intensity data have been published is used to test this scenario. This event is analyzed using a two-dimensional Gleeson-Axford equation to describe the shock acceleration process and a model bow shock whose nose serves as a uniform source of ions injected into the acceleration process. Intensity-time profiles are calculated for 30-keV and 120-keV protons for a range of diffusion coefficients using connection times that are based on the shock geometry and the magnetic field data.
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; 9975-998
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  • 6
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    Hydromagnetic waves and cosmic ray diffusion theory (1975)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Pitch angle diffusion of cosmic rays in hydromagnetic wave fields is considered strictly within the quasilinear approximation. It is shown that the popular assumption of an isotropic power spectrum tensor of magnetic fluctuations requires in this case equal forms and magnitudes of Alfven and magnetosonic wave spectra - a situation which is generally unlikely. The relative contributions to the pitch angle diffusion coefficient from the cyclotron resonances and Landau resonance due to the different types of waves are evaluated for a typical situation in the solar wind. Since in this approximation also the Landau resonance does not lead to particle reflections a proper consideration of the nonlinear particle orbits is indeed necessary to overcome the well known difficulties of quasilinear scattering theory for cosmic rays near 90 degrees pitch angle.
    Keywords: SPACE RADIATION
    Type: International Cosmic Ray Conference; Aug 15, 1975 - Aug 29, 1975; Munich
    Format: text
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  • 7
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    The spatial distribution of ultraviolet line and continuum emission in Herbig-Haro objects (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Archival IUE data and monochromatic CCD images in the optical range are used to compare the spatial distribution of UV and optical emission in HH 1, HH 2, HH 24, HH 32, HH 43, and HH 47. For all six objects, the observed UV radiation is shown to originate in the objects themselves. The results indicate that the C IV and semiforbidden emission-line regions are small. Although the continuum in the IUE short-wavelength range displays a distribution that is broader than that of any measured line emission in the UV or optical range, the continuum distribution in the IUE long-wavelength range is quite narrow.
    Keywords: SPACE RADIATION
    Type: Astronomical Journal (ISSN 0004-6256); 96; 1690-170
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  • 8
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    A perturbation approach to cosmic ray transients in interplanetary space (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A perturbation approach is used to model the linear response of the cosmic ray distribution as a function of perturbations in the solar wind transport parameters. The analytical technique permits examination of the effects of the different solar wind parameters, i.e., velocity, drift velocity and the diffusion tensor, which are additive. Cosmic ray changes in the solar wind are neglected. Variations in the diffusion coefficient and the convection-diffusion equation are applied to describing Forbush decreases and the 11-yr solar cycle variations. The treatment is limited to energies above 100 MeV, yet is considered valid enough to have identified a hysteresis effect in the 11-yr variation, wherein high-energy particles lead low-energy particles to a magnitude that increases with increasing heliocentric distance within the inner heliosphere. The calculations also indicate that the Forbush decreases are a cumulative effect of precipitous precursors accompanied by slow recoveries from travelling solar wind perturbations.
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 2903-291
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