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  • Other Sources  (6)
  • ASTROPHYSICS  (6)
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  • Other Sources  (6)
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  • 1
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    The LXeCAT instrument for gamma-ray astrophysics (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Liquid Xenon Coded Aperture Telescope (LXeCAT) and its capability to image astrophysical gamma-ray sources in the MeV region is described. The gamma-ray detector is a Liquid Xenon Time Projection Chamber (LXeTPC) triggered by the primary scintillation light. Effective background rejection is a direct consequence of the intrinsic three-dimensional imaging capability of the LXeTPC. Initial results with a 10 liter prototype confirm an energy resolution of 6% FWHM, a position resolution of 1 mm RMS and a light triggering efficiency higher than 90% for 1 MeV gamma-rays.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-199796 , NAS 1.26:199796 , NIPS-95-06474
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Limit on galactic 6.13 MeV gamma-ray line (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The University of New Hampshire large gamma-ray detector observed the galactic center region during a balloon flight from Alice Springs, Australia on 1977 November 21-22. The absence of any observable line at 6.13 MeV or its escape-peak energy makes it possible to place an upper limit of 8.1 x 10 to the -4th photons/(sq cm s) at the 99% confidence level on the 0-16 de-excitation line at this energy from the galactic disk in the direction of the center. This limit restricts the interpretation given by Willett et al. (1979) of the line at 6.13 MeV which they observed while viewing the galactic anticenter. The present results indicate that it is highly unlikely that the line which these authors report is due to dark nebulae or the quiet sun. Possible explanations for their observation are atmospheric background, local production in the detector, a localized cosmic source in the direction of the galactic anticenter, or a statistical fluctuation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 244
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Statistical evaluation of gamma-ray line observations (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The statistical reliability of reported positive observations of solar and cosmic gamma-ray lines has been evaluated. The relative probability that each measurement is due to a real source rather than to an accidental fluctuation in the background has been determined, and it is found that the results are statistically compelling in only a small fraction of the reported observations. At present, extreme caution must be exercised in drawing astrophysical conclusions from reports of the detection of cosmic gamma-ray lines.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 242
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Gamma-ray observations of Cygnus X-1 and Cygnus X-3 using a coded-aperture telescope (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A balloon-borne coded-aperture telescope, measuring gamma-ray photons in the 160 keV to 9.3 MeV range, was used to observe the Cygnus region of the sky on October 1 and 2, 1984. In the 2-9.3-MeV band, evidence is found for a hard spectral component with a mean flux level at the top of the atmosphere of 7.4 + or - 2.5 x 10 to the -7th photons/sq cm per s per keV, inconsistent with the predictions of the inverse Compton models normally used to describe the X-ray emission. Both Cyg X-1 and Cyg X-3 could be observed simultaneously with the telescope. The results are used to establish 1-sigma upper flux limits on the spectral emission from Cyg X-3.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 343; 317-322
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Effects of line width and spatial extent on measurements of the 0.51 MeV Galactic center line (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Over the past 15 years, a number of measurements have been made of positron-electron annihilation radiation from the Galactic Center region. The results after 1979 show a significant decrease in measured flux intensity from that previously observed with the same instruments. This is probably due to time variations; however, the contributions of a spatially extended and/or energy-broadened component should also be considered. The entire data set is consistent with a time variable point source plus a distribution along the Galactic Disk. There is no strong evidence for a component broadened in energy.
    Keywords: ASTROPHYSICS
    Type: Positron-electron pairs in astrophysics; Jan 06, 1983 - Jan 08, 1983; Greenbelt, MD
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Gamma-ray observations of the Crab Region using a coded-aperture telescope (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The region of the Galactic anticenter, including the Crab Nebula, was observed during a balloon flight of the University of New Hampshire Directional Gamma-Ray Telescope employing the coded-aperture imaging technique to image celestial gamma-radiation between 160 keV and 9.3 MeV. The background systematics are treated with a simple and relatively straightforward correction procedure. The results demonstrate that the coded-aperture procedure is a viable approach for imaging not only point sources of radiation, but also extended sources of emission. The results for the Crab's photon spectrum are consistent with a power-law spectrum. Upper limits on the flux levels of line emission at 405 keV and 1050 keV and on the flux from the X-ray binary source A0535 + 26 and diffuse Galactic emission from the anticenter region are derived.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 321; 543-552
    Format: text
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    NASA TECHNICAL REPORTS
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