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  • SPACE RADIATION  (4)
  • 1990-1994  (4)
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  • 1
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    Compton scattering in jets: A mechanism for approximately 0.4 and less than or approximately 0.2 MeV line production (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We show that gamma-ray line emission at approximately 0.4 and less than or approximately 0.2 MeV can be produced by Compton scattering of beamed radiation in the jets of Galactic black hole candidates. This mechanism has the novel feature of not invoking the presence of e(exp +)-e(exp -) pairs. To produce the two lines, we employ a symmetric double-sided jet with bulk flow velocity of about 0.5c and incident beam radiation with a hard energy spectrum. We show that the two lines can be seen at viewing-angle cosines relative to the jet ranging from 0.2 to 0.6. This comprises 40% of the total solid angle. In addition, the line radiation is approximately 10% polarized. Depending on the bulk flow and viewing angle, the model can produce lines at other energies as well. In particular, a broad feature near 1 MeV can be seen by viewing the jet close to its axis. Our model can also accommodate single-line spectra if the beamed gamma-ray emission or the jets themselves are asymmetric.
    Keywords: SPACE RADIATION
    Type: The Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 431; 1; p. L39-L42
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    The Energetic Particles Acceleration, Composition, and Transport (EPACT) experiment on the ISTP/wind spacecraft (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The EPACT experiment will measure abundances, spectra, and angular distributions of particles from 20 keV/amu to 500 MeV/amu. At high energies, isotopes will be resolved up through Z = 26, at intermediate energies elements with Z between 1 and 82 will be observed, and at low energies element abundances above Z = 2 will be resolved for the first time.
    Keywords: SPACE RADIATION
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    On the origin of variable 511 keV line emission from the Galactic center region (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Variable narrow-line emission at 511 keV, due to positron annihilation, has been observed from the region of the Galactic center for over a decade with high-resolution Ge spectrometers. The variable nature of this emission suggests that a significant fraction of the observed radiation is produced by a single source in the central region of the Galaxy. Recent observations with an imaging gamma-ray spectrometer of low energy resolution have revealed a daylong burst of annihilation radiation from the X-ray source 1E 1740.7-2042 located at an angular distance of 0.9 deg from the Galactic center and aligned with a dense molecular cloud. It is proposed that the variable narrow 511 keV line emission is due to positrons released impulsively (time scale of about 1 day) from 1E 1740.7-2942 into the molecular cloud where they slow down and annihilate on a longer time scale of up to a year.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 392; 2 Ju
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    The NASA cosmic ray program for the 1990's and beyond (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: The interim report of the 1989 NASA Cosmic Ray Program Working Group is presented. The report summarizes the cosmic ray program for the 1990's, including the recently approved ACE, Astromag, HNC, POEMS, and SAMPEX missions, as well as other key elements of the program. New science themes and candidate missions are identified for the first part of the 21st century, including objectives that might be addressed as part of the Human Exploration Initiative. Among the suggested new thrusts for the 21st century are: an Interstellar Probe into the nearby interstellar medium; a Lunar-Based Calorimeter to measure the cosmic ray composition near 10 exp 16 eV; high-precision element and isotope spectroscopy of ultraheavy elements; and new, more sensitive studies of impulsive solar flare events.
    Keywords: SPACE RADIATION
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    NASA TECHNICAL REPORTS
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