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  • ASTRONOMY  (4)
  • SPACECRAFT INSTRUMENTATION  (1)
  • 1990-1994  (4)
  • 1985-1989  (1)
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  • 1
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    COMPTEL: Instrument description and performance (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The imaging Compton telescope (COMPTEL) is one of the four gamma ray detectors aboard the Compton Gamma Ray Observatory (GRO). COMPTEL is sensitive to gamma rays from 800 keV to 30 MeV with a field of view of approximately 1 sr. Its angular resolution ranges between 1 and 2 degrees depending on the energy and incidence angle. The energy resolution of better than 10 percent FWHM enables COMPTEL to provide spectral resolution in the regime of astrophysical nuclear lines. The effective area varies typically from 10 to 50 cm(exp 2) depending on the energy and event selections made. In its telescope mode, COMPTEL is able to study a wide variety of objects, pointlike as well as extended in space. With 0.125 msec timing resolution, pulsed emission can be studied. In the single detector mode, COMPTEL uses two of its detectors to study the temporal spectral evolution of strong gamma ray bursts or transients.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center, The Compton Observatory Science Workshop; p 85-94
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    COMPTEL observations of Ti-44 gamma-ray line emission from Cas A (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Compton Telescope (COMPTEL) telescope aboard the Compton Gamma-Ray Observatory (CGRO) is capable of imaging gamma-ray line sources in the MeV region with a sensitivity of the order 10(exp -5) photons/(sq cm s). During two observations periods in July 1992 and February 1993 the Galactic plane in the region of the young supernova remnant Cas A was observed, showing evidence for line emission at 1.16 MeV from the decay of Ti-44 at a significance level of approximately 4 sigma. This is the first time a supernova remnant has been detected in the gamma-ray line from Ti-44 decay. Adopting a distance of 2.8 kpc to the Cas A remnant, the measured line flux (7.0 +/- 1.7) x 10(exp -5) photons/(sq cm s), can be translated into a Ti-44 mass ejected during the Cas A supernova explosion, between (1.4 +/- 0.4) x 10(exp -4) solar mass and (3.2 +/- 0.8) x 10(exp -4) solar mass, depending on the precise value of the Ti-44 mean life time and on the precise date of the event. Implications of this result for supernova nucleosynthesis models are discussed.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 284; 1; p. L1-L4
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    COMPTEL observations of the 1.809 MeV gamma-ray line from galactic Al-26 (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The COMPTEL experiment on the Compton Gamma-Ray Observatory (CGRO) has been demonstrated to be capable of imaging the Galaxy within its field of view of about 1 steradian in the 1.809 MeV gamma-ray line originating from radioactive Al-26. The combined data from the CGRO sky survey in 1991/1992 have been analyzed to provide a first map of the inner Galaxy in this gamma-ray line. The 1.809 MeV emission appears extended along the inner 70 deg of the Galactic plane, with a relatively sharp falloff outside this regime. Correlations with massive stars and supernova remnants as possible tracers of the candidate Al-26 sources are discussed.
    Keywords: ASTRONOMY
    Type: The Astrophysical Journal Supplement Series (ISSN 0067-0049); 92; 2; p. 429-432
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    A direct evaluation of the Geosat altimeter wet atmospheric range delay using very long baseline interferometry observations (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The overall accuracy of the U.S. Navy Geosat altimeter wet atmospheric range delay caused by refraction through the atmosphere is directly assessed by comparing the estimates made from the DMSP Special Sensor Microwave/Imager and the U.S. Navy Fleet Numerical Ocean Center forecast model for Geosat with measurements of total zenith columnar water vapor content from four VLBI sites. The assessment is made by comparing time series of range delay from various methods at each location. To determine the importance of diurnal variation in water vapor content in noncoincident estimates, the VLBI measurements were made at 15-min intervals over a few days. The VLBI measurements showed strong diurnal variations in columnar water vapor at several sites, causing errors of the order 3 cm rms in any noncoincident measurement of the wet troposphere range delay. These errors have an effect on studies of annual and interannual changes in sea level with Geosat data.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: International Journal of Remote Sensing (ISSN 0143-1161); 14; 9; p. 1723-1733.
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Radio-source positions from VLBI (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Positions of 85 compact extragalactic radio sources and the Galactic object Beta Persei (Algol) have been determined in the J2000.0 coordinate system for analysis of VLBI observations made with the bandwidth-synthesis technique. Twenty-four of these sources were observed with the Mark I VLBI system in 37 sessions distributed between April 1972 and May 1978, and 82 of the sources were observed with the Mark III system in 85 sessions distributed between August 1979 and December 1982. Each session spanned at least 24 hr. Standard errors for the estimated positions on the sky of the about 10 sources frequently observed with the Mark I system are about 1 mas, except for the declinations of nearly equatorial sources, where these errors approach 5 mas. Corresponding uncertainties for the about 20 sources frequently observed with the Mark III system are 0.3 and 2 mas, respectively.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 92; 1020-102
    Format: text
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    NASA TECHNICAL REPORTS
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