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  • 1
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    Pulsed high-energy gamma-rays from the radio pulsar PSR1706-44 (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Gamma radiation above 100 MeV in energy has been detected from the radio pulsar PSR1706-44. The gamma emission forms a single broad peak within the pulsar period of 102 ms, in contrast to the two narrow peaks seen in the other three known high-energy gamma-ray pulsars. The emission mechanism in all cases is probably the same, the differences arising from the geometry of the magnetic and rotation axes and the line of sight. Gamma-ray emission accounts for as much as 1 percent of the total neutron star spindown energy in these pulsars, much more than emerges at optical or radio frequencies. Thus, study of this emission is important in understanding pulsar emission and evolution.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 359; 6396; p. 615, 616.
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  • 2
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    Observation of gamma ray bursts and flares by the EGRET telescope on the Compton Gamma Ray Observatory (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory has observed energetic gamma ray bursts and flares. On May 3, 1991, EGRET detected a gamma ray burst both in the energy measuring NaI (Tl) scintillator and independently in the spark chamber imaging assembly. The NaI spectra were accumulated by a special BURST mode of EGRET. The spectra were measured over a range from 1 to 200 MeV, in three sequential spectra of 1,2, and 4 seconds. During the peak of the burst, six individual gamma rays were detected in the spark chamber, allowing a determination of the burst arrival direction. The intense flares of June were also detected. A solar flare on June 4 was observed to last for several minutes and for a brief time, less than a minute, had significant emission of gamma rays exceeding 150 MeV.
    Keywords: SPACE RADIATION
    Type: In: Gamma-ray bursts; Proceedings of the Workshop, Univ. of Alabama, Huntsville, Oct. 16-18, 1991 (A93-40051 16-93); p. 38-42.
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  • 3
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    A search for primeval galaxies (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We are conducting a search for emission-line objects at large redshifts, ostensibly young and forming galaxies. Our method is to search for strong line emission, in particular Ly-alpha, using two techniques: a direct, narrow-band imaging search using a Fabry-Perot interferometer; and a serendipitous long-slit spectroscopic search. Assuming that none of the faint candidates found so far are actually primeval galaxies, we can set the strongest limits to date on the surface density of Ly-alpha-luminous primeval galaxies on the sky. Some of the faint emission line galaxies detected in our survey at z roughly 0.5 - 1 may be representative of the faint blue galaxy population detected in deep continuum imaging surveys.
    Keywords: ASTRONOMY
    Type: In: The space distribution of quasars; Proceedings of the Workshop, Victoria, Canada, June 3-5, 1991 (A93-28776 10-90); p. 354-357.
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  • 4
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    Calibration of the Energetic Gamma-Ray Experiment Telescope (EGRET) for the Compton Gamma-Ray Observatory (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The calibration of the (EGRET) prior to its launch aboard the Compton Gamma Ray Observatory, the continuing calibration after launch, and instrument-performance results based on calibrations and early postlaunch data, are described. Particular attention is given to the effective area, the annular resolution, and the energy resolution.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 86; 2; p. 629-656.
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  • 5
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    SAS 2 observation of pulsed high-energy gamma radiation from Geminga (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Following the detection of pulsed X-rays and gamma rays from Geminga, the 1972-1973 SAS 2 data which first revealed this source have been reanalyzed. The 237 ms periodicity is visible in those observations. The phase of the SAS 2 periodicity is consistent with that of COS B suggesting that the gamma-ray data allow an accounting for every revolution of the Geminga pulsar between 1972 and 1982.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 401; 1; p. L23-L26.
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  • 6
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    Large and small scale circulation signatures of the ERS-1 SAR over the Gulf Stream (1994)
    In:  CASI
    Details
    Publication Date: 2005-09-21
    Description: Since September 1991, the ERS-1 SAR (Synthetic Aperture Radar) has collected approximately 170 frames of ocean imagery on 28 passes over the western Gulf Stream in support of ESA experiment US8-2c. SAR signatures of the north wall are seen on nearly all passes, with modulation depth varying from 3% to 35% for 100 m samples. Many small and mesoscale circulation features associated with the Stream are evident. The detailed form of the signature varies considerably, however. Narrow bright or dark linear features appear to follow streamlines, and on one occasion a strong dark line was associated with an in situ measurement of a sharp current shear. Similarly, larger spatial scale changes in backscatter over the Stream were associated with in situ measurements of atmospheric stability transitions. Physical explanations for the narrow features are not so obvious. However, the accumulation of surfactants along converging current boundaries or local short wave straining and breaking appear plausible. These preliminary results strongly suggest that a wide swath (approximately 500 km) SAR with at least 100 m resolution would be a useful adjunct to existing satellite AVHRR (Advanced Very High Resolution Radiometer) imagery.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: ESA, Proceedings of the Second ERS-1 Symposium on Space at the Service of Our Environment, Volume 1; p 547-552
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  • 7
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    Detection of high-energy gamma radiation from quasar 3C 279 by the EGRET telescope on the Compton Gamma Ray Observatory (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Intense gamma radiation has been observed from the direction of the quasar 3C 279 throughout the energy range from 30 MeV to over 5 GeV by the Energetic Gamma Ray Experiment Telescope (EGRET) during the period June 15-28, 1991. Its spectrum is well represented by a photon differential power-law exponent of 2.0 +/- 0.1, with a photon intensity above 100 MeV of (2.8 +/- 0.4) x 10 exp -6/sq cm s. For E is greater than 100 MeV, the 2-sigma upper limits were 1.0 x 10 exp -6/sq cm s in 1973 from the SAS 2 observations and 0.3 x 10 exp -6/sq cm s for the combined 1976, 1978, and 1980 COS B observations. Hence, there has been a large increase in high-energy gamma-ray intensity relative to the earlier times, as there has been in the radio, infrared, optical, and X-ray ranges. This source is the most distant and by far the most luminous gamma-ray source yet detected.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 385; L1-L4
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  • 8
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    Europa's phase curve - Implications for surface structure (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The surface of the Jovian satellite Europa is characterized on the basis of an analysis of ground photoelectric photometry at 470 and 550 nm and Voyager images. The data are presented in extensive tables and graphs and discussed in detail. At 550 nm, Europa has single-scattering albedo 0.964, opposition-effect amplitude 0.5, opposition-effect width 0.0016, double-lobed Henyey-Greenstein factors b = -0.429 and c = 0.113, and mean roughness angle 10 deg (much lower than on other solar-system objects). From the small roughness and the 96-percent porosity implied by the narrow opposition peak, it is concluded that the surface was formed mainly by endogenic processes. It is also noted that only one of three observational criteria for preferential ion bombardment of the trailing hemisphere are met in Europa.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 90; 30-42
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  • 9
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    A search for quasar protoclusters at z greater than 4 (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: In the CDM and many other hierarchical scenarios for the origins of large scale structure, the existence of luminous quasars at very high redshifts (z greater than 3 or 4) is difficult to understand, unless such objects form at the very highest peaks of the density field. One then might expect a strong clustering of quasars at large redshifts. This is a generic prediction for practically any reasonable primordial density fluctuation spectrum. For CDM, Efstathiou & Rees (1988) predicted that quasars at z greater than 4 should be clustered as strongly as the bright galaxies at z approx. than 0. Cole & Kaiser (1989) suggest that z greater than 4 quasars might represent greater than or approximately = 4(sigma) peaks of the density field and thus, should be clustered more strongly than galaxies at z approximately = 0. We are performing the following experiment: a search for quasars, AGN, or other discrete objects, e.g., starforming galaxies, near known, z greater than 4 quasars. In other words, use the early quasars as markers of possible protoclusters. This is a fairly basic test of our understanding of the formation of galaxies, large-scale structure, and the origin of the first quasars themselves.
    Keywords: ASTROPHYSICS
    Type: NASA. Ames Research Center, The Evolution of Galaxies and Their Environment; p 36-37
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  • 10
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    Two searches for primeval galaxies (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A number of active galaxies are now known at very large redshifts, some of them even have properties suggestive of galaxies in the process of formation. They commonly show strong Ly-alpha emission, at least some of which appears to be ionized by young stars. Inferred star formation rates are in the range approximately = 100-500 solar mass/yr. An important question is: are there radio-quiet, field counterparts of these systems at comparable redshifts? Whereas, we are probably already observing some evolutionary and formative processes of distant radio galaxies, the ultimate goal is to observe normal galaxies at the epoch when most of their stars form. We have, thus, started a search for emission-line objects at large redshifts, ostensibly young and forming galaxies. Our method is to search for strong line emission (hopefully Ly alpha) employing two techniques: a direct, narrow-band imaging search, using a Fabry-Perot interferometer; and a serendipitous long-slit spectroscopic search.
    Keywords: ASTROPHYSICS
    Type: NASA. Ames Research Center, The Evolution of Galaxies and Their Environment; p 23-24
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