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  • SPACE RADIATION  (31)
  • GEOPHYSICS
  • 1975-1979  (31)
  • 1
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    SAS-2 galactic gamma-ray results. 2: Localized sources (1977)
    In:  CASI
    Details
    Publication Date: 2006-08-09
    Description: Gamma ray emission was detected from the radio pulsars PSR 1818-04 and PSR 1747-46, in addition to the previously reported gamma ray emission from the Crab and Vela pulsars. Because the Crab pulsar is the only one observed in the optical and X-ray bands, these gamma ray observations suggest a uniquely gamma ray phenomenon occurring in a fraction of the radio pulsars. PSR 1818-04 has a gamma ray luminosity comparable to that of the Crab pulsar, whereas the luminosities of PSR 1747-46 and the Vela pulsar are approximately an order of magnitude lower. SAS-2 data for pulsar correlations yielded upper limits to gamma ray luminosity for 71 other radio pulsars. For five of the closest pulsars, upper limits for gamma ray luminosity are found to be at least three orders of magnitude lower than that of the Crab pulsar. Gamma ray enhancement near the Milky Way satellite galaxy and the galactic plane in the Cygnus region is also discussed.
    Keywords: SPACE RADIATION
    Type: The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 15-26
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  • 2
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    SAS-2 galactic gamma-ray results. 1: Diffuse emission (1977)
    In:  CASI
    Details
    Publication Date: 2006-08-09
    Description: Continuing analysis of the data from the SAS-2 high energy gamma ray experiment has produced an improved picture of the sky at photon energies above 35 MeV. On a large scale, the diffuse emission from the galactic plane is the dominant feature observed by SAS-2. This galactic plane emission is most intense between galactic longitudes 310 deg and 45 deg, corresponding to a region within 7 kpc of the galactic center. Within the high-intensity region, SAS-2 observes peaks around galactic longitudes 315, 330, 345, 0, and 35 deg. These peaks appear to be correlated with galactic features and components such as molecular hydrogen, atomic hydrogen, magnetic fields, cosmic-ray concentrations, and photon fields.
    Keywords: SPACE RADIATION
    Type: The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 3-14
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  • 3
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    SAS-2 galactic gamma ray results, 1 (1976)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: Continuing analysis of the data from the SAS-2 high energy gamma-ray experiment has produced an improved picture of the sky at photon energies above 35 MeV. On a large scale, the diffuse emission from the galactic plane is the dominant feature observed by SAS-2. This galactic plane emission is most intense between galactic longitude 310 and 45 deg, corresponding to a region within 7kpc of the galactic center. Within the high-intensity region, SAS-2 observes peaks around galactic longitudes 315 deg, 330 deg, 345 deg, 0 deg, and 35 deg. These peaks appear to be correlated with such galactic features and components as molecular hydrogen, atomic hydrogen, magnetic fields, cosmic ray concentrations, and photon fields.
    Keywords: SPACE RADIATION
    Type: The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 1-11C
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  • 4
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    Gamma rays and large scale galactic structure (1976)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: Many theoretical models were developed in an attempt to explain the spatial structure in the observed emission which results from interactions of energetic cosmic rays with the interstellar gas. The peaks in the observed distribution are remarkably well correlated with longitudes corresponding to tangential directions to known spiral arm features. Based on theoretical and experimental arguments, it is assumed that on the scale of galactic arms the cosmic rays are more intense where the mass of the gas to which they are coupled is greatest. Refining this model with the results of recent surveys of the interstellar gas, a good fit to the observations is obtained whether the cosmic rays are confined to the spiral arms in the disk or are more evenly confined as in a flat halo model.
    Keywords: SPACE RADIATION
    Type: The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 341-354
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  • 5
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    SAS-2 galactic gamma ray results. 2. Localized sources (1976)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: Gamma-ray emission was detected from the radio pulsars PSR1818-04 and PSR1747-46, in addition to the previously reported gamma-ray emission from the Crab and Vela pulsars. Since the Crab pulsar is the only one observed in the optical and X-ray bands, these gamma-ray observations suggest a uniquely gamma-ray phenomenon occurring in a fraction of the radio pulsars. Using distance estimates it is found that PSR1818-04 has a gamma-ray luminosity comparable to that of the Crab pulsar, while the luminosities of PSR1747-46 and the Vela pulsar are approximately an order of magnitude lower. This survey of SAS-2 data for pulsar correlations has also yielded upper limits to gamma-ray luminosity for 71 other radio pulsars.
    Keywords: SPACE RADIATION
    Type: The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 12-22
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  • 6
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    High-energy galactic gamma radiation from cosmic rays concentrated in spiral arms (1975)
    In:  Other Sources
    Details
    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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  • 7
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    SAS-2 high-energy gamma-ray observations of the Vela pulsar. II (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Analysis of additional data from SAS-2 experiment and improvements in the orbit-attitude data and analysis procedures have produced revised values for the flux from the Vela gamma-ray source. The pulsar phase plot shows two peaks, neither of which is in phase with the single radio pulse.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal; vol. 214
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  • 8
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    Final SAS-2 gamma-ray results on sources in the galactic anticenter region (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Final results are presented for SAS-2 observations of high-energy gamma-rays from the galactic anticenter region. Three main gamma-ray features are shown to characterize this region: a localized source associated with the Crab Nebula and its pulsar, another localized source near galactic coordinates 195 deg, +5 deg, and a general enhancement of the diffuse background 10 to 15 deg south of the galactic plane, which is associated with the Gould Belt. For the Crab, it is found that the radiation is mostly pulsed, the pulsed fraction increases with energy, and the intensity of the radiation in the main and interpulse peaks is approximately the same. The other localized source, provisionally designated as gamma 195+5, is found to have a harder spectrum than the Crab but no obvious radio counterpart; emission from an external galaxy is ruled out.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal; vol. 213
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  • 9
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    Observation of gamma rays with a 4.8 hour periodicity from Cygnus X-3 (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Energetic (exceeding 35 MeV) gamma-rays have been observed from the direction of Cygnus X-3 with the SAS-2 gamma-ray telescope. The statistical significance of the excess above the galactic and diffuse radiation is approximately 4.5 sigma. In addition, the gamma-ray flux is modulated at the 4.8-hr period observed in the X-ray and infrared regions, and within the statistical error is in phase with this emission. The flux above 100 MeV has an average value of about 4.4 millionths photon/sq cm per sec. If the distance to Cygnus X-3 is 10 kpc, this flux implies a luminosity of more than 10 to the 37th power erg/s if the radiation is isotropic and about 10 to the 36th power erg/s if the radiation is restricted to a cone of 1 steradian, as it might be in a pulsar. Upper limits are presented for the gamma-ray flux from other known or suspected periodic X-ray sources.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal; vol. 212
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  • 10
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    SAS-2 observations of the diffuse gamma radiation in the galactic latitude interval from 10 to 90 deg in both hemispheres (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: An analysis of all the second Small Astronomy Satellite (SAS-2) gamma-ray data for galactic latitudes higher than 10 deg in both hemispheres has shown that the intensity varies with galactic latitude, being larger near 10 deg than 90 deg. For energies above 100 MeV the gamma-ray data are consistent with a latitude distribution of the form I(b) = C1 + C2/sin b, with the second term being dominant. This result suggests that the radiation above 100 MeV is coming largely from local regions of the galactic disk. Between 35 and 100 MeV, a similar equation is also a good representation of the data, but here the two terms are comparable. These results indicate that the diffuse radiation above 35 MeV consists of two parts, one with a relatively hard galactic component and the other an isotropic steep spectral component which extrapolates back well to the low-energy (less than 10 MeV) diffuse radiation. The steepness of the diffuse isotropic component places significant constraints on possible theoretical models of this radiation.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal; vol. 217
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