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  • 1
    Publication Date: 2011-08-16
    Description: A model for the emission of high-energy (exceeding 100 Mev) gamma-rays from the galactic disk has been developed and compared with recent SAS-2 observations. In the calculation, it is assumed that (1) the high energy galactic gamma-rays result primarily from the interaction of cosmic rays with galactic matter, (2) the cosmic-ray density is proportional to the matter density on the scale of galactic arms, and (3) the matter in the Galaxy is distributed in a spiral pattern consistent with density-wave theory and experimental data on the matter distribution that is available, including the 21-cm H I line emission, continuum emission from H II regions, and data currently being used to estimate the H2 density. The calculated galactic-longitude distribution of gamma rays is in good agreement with the SAS-2 observations in relative shape and absolute flux. As a corollary, the nonuniform cosmic-ray distribution of this model tends to support the galactic origin of the fraction of cosmic rays which is important in the production of high-energy photons. Modifications of the basic model show that the gamma-ray flux is relatively sensitive to large variations of the assumed distribution of molecular hydrogen in the Galaxy.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal; 199; July 1
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  • 2
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    In:  Other Sources
    Publication Date: 2019-06-27
    Description: The composite spectrum of gamma-rays is calculated which results from the decay of Ni-56 to Co-56 to Fe-56 throughout the history of the universe. The results for several cosmological models are presented and compared with the Apollo 15 measurements at low resolution of the cosmic background. The radioactivity background is a significant fraction of the total, and several of its features may be detectable.-
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal; 198; June 1
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  • 3
    Publication Date: 2019-06-27
    Description: The cosmic ray intensity variations over the energy range of about 0.5 MeV to 1 GeV during the early part of August 5 are discussed in relation to the intensity changes during the entire period of activity (August 2 to 11). Measurements of the interplanetary magnetic field and particle data from ground-based neutron monitors, lunar sensors, and detectors in board Explorers 41 and 43 are used in the investigation. Analysis is made of intensity changes during the period from 0200 to 0700 UT on August 5, the north-south asymmetry in neutron monitor intensities, changes in the alpha particle/proton flux ratios, the lag in onset times as recorded by the two Explorers, and observations of flux enhancement by the lunar detectors. The results indicate that the enhanced particle fluxes (about 1 GeV) were due to a leakage of galactic cosmic rays into a low-intensity region of the interplanetary magnetic field bounded by tangential discontinuities, which connected to different particle sources both near the sun and in the outer solar system.
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research; 80; May 1
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  • 4
    Publication Date: 2019-06-27
    Description: A cosmic gamma-ray burst is reported that occurred at 29309.11 s UTC, May 14, 1975. The burst was detected at an atmospheric depth of 4 g/sq cm residual atmosphere with the University of California double scatter gamma-ray telescope launched on a balloon from Palestine, Texas at 1150 UTC, May 13, 1975. The burst was observed both in the single scatter mode by the top liquid scintillator tank in anti-coincidence with the surrounding plastic scintillator and in the double scatter mode from which energy and directional information are obtained. The burst is 24 standard deviations above the background for single scatter events. The total gamma-ray flux in the burst, incident on the atmosphere with photon energy greater than 0.5 MeV, is 0.59 + or - 0.15 photons/sq cm. The initial rise time to 90% of maximum is 0.015 + or - 0.005 s and the duration is 0.11 s. Time structure down to the 5 ms resolution of the telescope is seen. The mean flux over this time period is 5.0 + or - 1.3 photons/sq cm/s and the maximum flux is 8.5 + or - 2.1 photons/sq cm/s.
    Keywords: SPACE RADIATION
    Type: NASA-CR-146333 , AD-A015673 , IGPP-UCR-75-16
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  • 5
    Publication Date: 2019-06-27
    Description: Medium energy (about 10 to 30 MeV) gamma ray astronomy provides information on the product of the galactic electron cosmic ray intensity and the galactic matter to which the electrons are dynamically coupled by the magnetic field. Because high energy (greater than 100 MeV) gamma ray astronomy provides analogous information for the nucleonic cosmic rays and the relevant matter, a comparison between high energy and medium energy gamma ray intensities provides a direct ratio of the cosmic ray electrons and nucleons throughout the galaxy. A calculation of gamma ray production by electron bremsstrahlung shows that: bremsstrahlung energy loss is probably not negligible over the lifetime of the electrons in the galaxy; and the approximate bremsstrahlung calculation often used previously overestimates the gamma ray intensity by about a factor of two. As a specific example, expected medium energy gamma ray intensities are calculated for the speral arm model.
    Keywords: SPACE RADIATION
    Type: NASA-TM-X-70988 , X-662-75-246
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  • 6
    Publication Date: 2019-07-13
    Keywords: SPACE RADIATION
    Type: International Cosmic Ray Conference; Aug 15, 1975 - Aug 29, 1975; Munich
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  • 7
    Publication Date: 2019-07-13
    Description: The high energy (above 35 MeV) gamma ray telescope flown on the second Small Astronomy Satellite has collected over one thousand gamma rays from the direction of the galactic anticenter. In addition to the diffuse galactic emission the distribution indicates a strong pulsed contribution from the Crab nebula with the same period and phase as the NP0532 pulsar. There also seems to be an excess in the direction of (gal. long. ? 195 deg; gal. lat ? +5 deg) where there is a region containing old supernova remnants. Search for gamma ray pulsations from other pulsars in the region do not show any statistically significant signal. The general intensity distribution of the gamma rays away from the plane appear to be similar to nonthermal radio emission brightness contours.
    Keywords: SPACE RADIATION
    Type: International Cosmic Ray Conference; Aug 15, 1975 - Aug 29, 1975; Munich
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  • 8
    Publication Date: 2019-07-13
    Description: Extending the model proposed by Bignami et al. (1975), and by Fichtel et al. (1975a) for the production of the galactic high energy gamma ray distribution observed by SAS-2 to lower energies indicates the radiation is dominated by the bremsstrahlung emission of cosmic ray electrons traversing the interstellar gas. Although secondary electrons contribute only about 15% to the 10-30 MeV gamma ray emission in the solar vicinity, their contribution in the model is proportional to the third power of N, where N(r, gal. long., gal. lat.) is the total interstellar gas density, as compared to the square of N for the case of the primary components, and hence their relative importance increases in high density regions. Gamma-ray observations at these energies when compared to those at high energies (above 100 MeV) may provide a means for mapping the ratio of cosmic ray electrons to nucleons throughout the galaxy without the necessity of invoking models for the galactic magnetic field.
    Keywords: SPACE RADIATION
    Type: International Cosmic Ray Conference; Aug 15, 1975 - Aug 29, 1975; Munich
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  • 9
    Publication Date: 2011-08-16
    Description: Spectral observations of nine recent cosmic gamma-ray bursts are reported. The average photon number spectra of all nine events are each consistent with a 150-keV exponential from 100 keV to about 400 keV, and a power law of index -2.5 from 400 keV to 1100 keV. The observations also indicate an event rate of 16 in 1972 and 1973, or 8 plus or minus 2 per year, higher than the 5 plus or minus 1 per year initially reported. This corresponds to an approximately 40 percent lower effective intensity threshold, attained by using more sensitive detectors in multiple-satellite coincidence.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal; 196; Feb. 15
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  • 10
    Publication Date: 2011-08-16
    Description: The present paper reports on the low-energy gamma-ray bursts observed by the plastic scintillator anticoincidence dome of the Small Astronomy Satellite-2 (SAS-2) gamma-ray telescope. SAS-2 detected two events observed by other satellites and discovered one which was subsequently confirmed by other satellite observations. Two events seen by other satellites were not detected by SAS-2, probably due to earth occultation. The event detection threshold for SAS-2 was almost two orders of magnitude lower than that of the Vela satellites.
    Keywords: SPACE RADIATION
    Type: Nature; 255; May 15
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