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  • ASTROPHYSICS  (6)
  • 1990-1994  (6)
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  • 1
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    Diffuse galactic annihilation radiation (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The study reports observations of positron annihilation radiation from the inner region of the Galaxy which show that there are two components of the radiation: a steady, diffuse Galactic component and a variable component from discrete, presumably compact sources. The existence of the variable component is supported by the ensemble of all narrow FOV 511 keV line observations, including recent detections with OSSE. The fit of this ensemble to a time-independent source distribution can be excluded at the approximately 3-sigma level. The same ensemble, combined with the broad FOV SMM observations of Galactic 511 keV line emission, sets constraints on the Galactic distribution of the diffuse component.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics Supplement Series (ISSN 0365-0138); 97; 1; p. 127-131.
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  • 2
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    Galactic dual population models of gamma-ray bursts (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We investigate in more detail the properties of two-population models for gamma-ray bursts in the galactic disk and halo. We calculate the gamma-ray burst statistical properties, mean value of (V/V(sub max)), mean value of cos Theta, and mean value of (sin(exp 2) b), as functions of the detection flux threshold for bursts coming from both Galactic disk and massive halo populations. We consider halo models inferred from the observational constraints on the large-scale Galactic structure and we compare the expected values of mean value of (V/V(sub max)), mean value of cos Theta, and mean value of (sin(exp 2) b), with those measured by Burst and Transient Source Experiment (BATSE) and other detectors. We find that the measured values are consistent with solely Galactic populations having a range of halo distributions, mixed with local disk distributions, which can account for as much as approximately 25% of the observed BATSE bursts. M31 does not contribute to these modeled bursts. We also demonstrate, contrary to recent arguments, that the size-frequency distributions of dual population models are quite consistent with the BATSE observations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 434; 2; p. 552-556
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  • 3
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    An observation of annihilation radiation from the Galactic center region (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Results are reported from observations of the 511 MeV annihilation gamma-ray line from the Galactic center, made on May 22, 1989 with a high-resolution gamma-ray spectrometer on board a balloon launched from Alice Springs (Australia). The observations were made at about 4 gm/sq cm atmospheric depth for 6 hrs in a series of target and background pointings lasting 20 min each. The results obtained from multiparameter Gaussian fits to the data were as follows: 511 keV flux = 0.00089 + or - 0.00027 ph/sq cm per sec-rad, line width of about 1.1 keV, and less than 3.2 keV FWHM at 95 percent confidence.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 11; 8 19
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  • 4
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    An observation of the Galactic center region with the HEXAGONE high resolution gamma-ray spectrometer (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The Galactic center region was observed for 6 hours on May 22, 1989 from a high altitude balloon with the HEXAGONE high resolution gamma-ray spectrometer. The instrument had a 285 sq/cm array of cooled germanium detectors with an energy resolution of 2.2 keV at 511 keV and an 18 deg FWHM field of view. The 511 keV gamma-rays from electron-positron annihilation and 1809 keV gamma-rays from the radioactive decay of Al-26 were observed to have fluxes of 8.9 x 10 exp -4 and 1.9 x 10 exp -4 ph/cm-s, respectively. Continuum emission was detected from 20 to 800 keV and preliminary results have been obtained for the spectrum. Below 120 keV this is well described by power law with a slope of -2.6. In the 120-250 keV band the spectrum contains a broad linelike feature. This is interpreted as the result of Compton backscattering of about 511 keV photons from a compact source of electron-positron annihilation radiation.
    Keywords: ASTROPHYSICS
    Type: International Symposium on Gamma-Ray Line Astrophysics; Dec 10, 1990 - Dec 13, 1990; Paris; France
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  • 5
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    Positron annihilation radiation from the Galactic center region (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Observations show that there are two components of positron annihilation radiation from the region of the Galactic center: a variable component resulting from one or just a few compact sources at or near the Galactic center and a steady, diffuse component resulting from positron annihilation in the Galactic disk. The diffuse component is modeled using the observed longitude distributions of 70-150 MeV gamma rays, CO, and hot plasma revealed by Fe line emission. Recent results on positron annihilation in the interstellar medium are reviewed and the implications of the annihilation processes on the fraction of positrons annihilating via positronium and on the shape of the 511 keV annihilation line are discussed. The sources of diffuse Galactic positrons are also reviewed and the nature of the compact source of annihilation radiation near the Galactic center is discussed.
    Keywords: ASTROPHYSICS
    Type: International Symposium on Gamma-Ray Line Astrophysics; Dec 10, 1990 - Dec 13, 1990; Paris; France
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  • 6
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    Are repeaters responsible for gamma-ray burst average V/V(max) less than 0.5? (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: We show that gamma-ray bursts, observed by the Konus experiment on Venera 11 and Venera 12, from the three identified sources of short-term repeating bursts have a very low average V/V(max) of only 0.17 +/- 0.10 and are very important contributors to the low average V/V(max) of 0.43 +/- 0.03 found from the entire Konus burst sample. We further point out that the expected number of additional, as yet unidentified, repeating sources is quite sufficient to account for the low Konus average V/V(max), assuming that the average V/V(max) for bursts from all other sources is 0.5. Thus we suggest that the class of short-term repeating gamma-ray burst sources, as yet only partially identified, are a high-luminosity population that could be responsible for the values of average V/V(max) less than 0.5 also found by the BATSE, SMM, and other gamma-ray burst experiments. We note, however, that repeating bursts cannot as yet be identified solely by their spectral and temporal properties.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 397; 2; p. 576-578.
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