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  • 11
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    The relationship between the galactic matter distribution, cosmic-ray dynamics, and gamma-ray production (1977)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-17
    Beschreibung: The concept that cosmic-ray density is related to the matter to which cosmic rays are dynamically coupled through magnetic fields on the scale of galactic arm segments is considered with specific reference to gamma-ray astronomy. A model of the galactic-matter and cosmic-ray distributions is developed on the basis of 21-cm radio surveys and recent observations of the 2.6-mm CO emission line by assuming that cosmic rays are galactic in origin, their column density is proportional to the total interstellar-gas column density, their scale height is considerably larger than that of the matter, and the Galaxy is a spiral with an arm/interarm density ratio of about 3 to 1. It is found that there is a good correlation between the observed gamma-ray intensity and that predicted on the basis of essentially complete coupling of cosmic rays to the best estimate of atomic and molecular hydrogen in the Galaxy. Individual maxima observed in gamma-radiation from the central region of the Galaxy are shown to be well correlated with those predicted to result from certain spiral-arm tangents if all the matter is assumed to be modulated in a particular spiral-arm segment pattern.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 215
    Format: text
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  • 12
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    A search of the SAS-2 data for pulsed gamma-ray emission from radio pulsars (1976)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Data from the SAS-2 high-energy (above 35 MeV) gamma-ray experiment have been examined for pulsed emission from each of 75 radio pulsars which were viewed by the instrument and which have sufficiently well-defined period and period-derivative information from radio observations to allow for gamma-ray periodicity searches. When gamma-ray arrival times were converted to pulsar phase using the radio reference timing information, two pulsars, PSR 1747-46 and PSR 1818-04, showed positive effects, each with a probability of less than 1 part in 10,000 of being a random fluctuation in the data for that pulsar. These are in addition to PSR 0531+21 and PSR 0833-45, previously reported. The results of this study suggest that gamma-ray astronomy has reached the detection threshold for gamma-ray pulsars and that work in the near future should give important new information on the nature of pulsars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; 209; Oct. 15
    Format: text
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  • 13
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    SAS-2 gamma-ray observations of PSR 1747-46 (1976)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Evidence is reported for the observation of gamma-ray emission from the radio pulsar PSR 1747-46 by the gamma-ray telescope aboard SAS 2. The evidence is based on the presence of both an approximately 3-sigma enhancement of gamma rays at the pulsar's location and an approximately 4-sigma peak in the phase plot of 79 gamma-ray events whose phase was calculated from the pulsar's known period. The gamma-ray pulsation is found to appear at a phase lag of about 0.16 from that predicted by the radio observations. The pulsed gamma-ray fluxes above 35 MeV and 100 MeV are estimated, and it is shown that the gamma-ray pulse width is similar to the radio pulse width. It is concluded that PSR 1747-46 is a most likely candidate for pulsed gamma-ray emission.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Letters; 17; 4, 19; 1976
    Format: text
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  • 14
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    Extragalactic gamma radiation - Use of galaxy counts as a galactic tracer (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-20109)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 109; 2, Ma; May 1982
    Format: text
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  • 15
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    A Systematic Search for Short-term Variability of EGRET Sources (2000)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-29
    Beschreibung: The 3rd EGRET Catalog of High-energy Gamma-ray Sources contains 170 unidentified sources, and there is great interest in the nature of these sources. One means of determining source class is the study of flux variability on time scales of days; pulsars are believed to be stable on these time scales while blazers are known to be highly variable. In addition, previous work has demonstrated that 3EG J0241-6103 and 3EG J1837-0606 are candidates for a new gamma-ray source class. These sources near the Galactic plane display transient behavior but cannot be associated with any known blazers. Although, many instances of flaring AGN have been reported, the EGRET database has not been systematically searched for occurrences of short-timescale (approximately 1 day) variability. These considerations have led us to conduct a systematic search for short-term variability in EGRET data, covering all viewing periods through proposal cycle 4. Six 3EG catalog sources are reported here to display variability on short time scales; four of them are unidentified. In addition, three non-catalog variable sources are discussed.
    Schlagwort(e): Astrophysics
    Format: application/pdf
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  • 16
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    Two searches for primeval galaxies (1993)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: 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.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Ames Research Center, The Evolution of Galaxies and Their Environment; p 23-24
    Format: application/pdf
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  • 17
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    High-spatial-resolution studies of young stellar objects. II - A thick disk surrounding Lynds 1551, IRS 5 (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Heavily oversampled, small (2 arcsec) beam 2 micron maps of the region surrounding Lynds 1551, IRS 5 provide the basis for reconstructing maximum-entropy 'images' which have an effective spatial resolution of about 0.6 arcsec. These images reveal an extended, cusp-like structure surrounding IRS 5. This structure most likely results as light from IRS 5 is scattered in our direction by dust grains located in a thick disk of diameter 1000 AU. The disk is viewed nearly edge-on and has a mass in dust grains of 2 to 5 x 10 to the -5th solar masses. Its polar axis lies along the observed direction of the bipolar mass outflow inferred from molecular line observations of the L1551 cloud. It is possible that the observed infrared disk may represent the inner regions of a much larger thick-disk structure, whose shape derives from the combined effects of disk rotation and the gravitational field of IRS 5.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal (ISSN 0004-6256); 90; 2575-258
    Format: text
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  • 18
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    The grains and gas in Comet Bowell 1980b (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The importance of coordinating different types of observations of a comet is illustrated in terms of spectral data on Comet Bowell. Photometric data in 1980 indicated that OH emissions were occurring when the comet was still more than 4 AU from the sun. Further measurements were arranged with the IUE satellite, the photoelectric scanner at Cerro Tololo and the IR telescope on Mauna Kea. Several sizes of diaphragms were used in order to estimate variations with respect to aperture. Calculations were made to quantify the wavelengths observed as a function of the grains' cross-sections. The OH emission was confirmed by the spectrographic and photometric data. It is suggested that sufficient dark materials are present on the cometary surface to have enhanced the absorption of solar radiation to levels sufficient for heating and dissociating surface ice particles.
    Schlagwort(e): ASTROPHYSICS
    Format: text
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  • 19
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    GLAST Large Area Telescope Multiwavelength Planning (2007)
    In:  CASI
    Details
    Publikationsdatum: 2018-06-06
    Beschreibung: Gamma-ray astrophysics depends in many ways on multiwavelength studies. The Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch of the observatory. Some of the high-priority multiwavelength needs include: (1) availability of contemporaneous radio and X-ray timing of pulsars; (2) expansion of blazar catalogs, including redshift measurements; (3) improved observations of molecular clouds, especially at high galactic latitudes; (4) simultaneous broad-spectrum blazar monitoring; (5) characterization of gamma-ray transients, including gamma ray bursts; (6) radio, optical, X-ray and TeV counterpart searches for reliable and effective sources identification and characterization. Several of these activities are needed to be in place before launch.
    Schlagwort(e): Astrophysics
    Format: application/pdf
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  • 20
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    Future Facilities for Gamma-Ray Pulsar Studies (2003)
    In:  CASI
    Details
    Publikationsdatum: 2018-06-06
    Beschreibung: Pulsars seen at gamma-ray energies offer insight into particle acceleration to very high energies, along with information about the geometry and interaction processes in the magnetospheres of these rotating neutron stars. During the next decade, a number of new gamma-ray facilities will become available for pulsar studies. This brief review describes the motivation for gamma-ray pulsar studies, the opportunities for such studies, and some specific discussion of the capabilities of the Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) for pulsar measurements.
    Schlagwort(e): Astrophysics
    Materialart: Young Neutron Stars and Their Environments: IAU Symposium; Volume 218; 1-6
    Format: application/pdf
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