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  • 1
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    SAS 2 observations of the earth albedo gamma radiation above 35 MeV (1981)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The earth albedo gamma radiation above 35 MeV in the equatorial region is investigated using observations from the second Small Astronomy Satellite. The zenith angle distribution of the gamma radiation has a peak toward the horizon which is about an order of magnitude more intense than the radiation coming from the nadir, and nearly two orders of magnitude more intense than the gamma radiation from most parts of the sky. The gamma radiation originating from the western horizon is a factor of four more intense than the radiation from the eastern horizon and a factor of three more intense than that from the northern and southern directions. This reflects the geomagnetic effects on the incident cosmic rays whose interactions produce the albedo gamma rays. The variation of the upcoming gamma ray intensity with vertical cutoff rigidity is consistent with the empirical relationship found by Gur'yan et al. (1979).
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; Mar. 1
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  • 2
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    A Systematic Search for Short-term Variability of EGRET Sources (2000)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: 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.
    Keywords: Astrophysics
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  • 3
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    GLAST Large Area Telescope Multiwavelength Planning (2007)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: 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.
    Keywords: Astrophysics
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  • 4
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    Future Facilities for Gamma-Ray Pulsar Studies (2003)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: 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.
    Keywords: Astrophysics
    Type: Young Neutron Stars and Their Environments: IAU Symposium; Volume 218; 1-6
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  • 5
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    An Intriguing Convex Break in the EGRET SED of Mrk 421 (2007)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Based upon analysis of the entire EGRET data from Mrk 421, it is found that the time-averaged spectra are inconsistent with the predictions of current theoretical models that have had success in describing simultaneous X-ray/TeV observations, and suggest additional components in the GeV band, as well as complex time variability. Current theoretical pictures explain the GeV emission as comptonization of the synchrotron photons in the jet, and predict hard spectra that should join smoothly with the TeV emission. Our analysis shows that the situation is more complex. The spectrum ranges from hard to soft during individual epochs, and shows a convext break in the aggregated data. We also present the mission-averaged EGRET spectrum for PKS 2155-304, which shows a similar (but not as pronounced) convex curvature. We discuss a series of possible explanations for the 10(exp 22) - 10(exp 23) HZ declining part of the EGRET nu F(sub nu), spectrum for Mrk 421, and suggest that it is synchrotron emission from the high energy tail of the electron population that produces the X-rays during the highest X-ray states. Such multi-MeV photons are produced by electrons accelerated close to the limit of diffusive shock acceleration. Simultaneous GLAST and X-ray observations of high X-ray states will address the issue of the convex curvature in the future.
    Keywords: Astrophysics
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  • 6
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    The Highest-Energy Photons Seen by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (2005)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: During its nine-year lifetime, the Energetic Gamma Ray Experiment Telescope (EGBET) on the Compton Gamma Ray Observatory (CGRO) detected 1506 cosmic photons with measured energy E〉10 GeV. Of this number, 187 are found within a 1 deg of sources that are listed in the Third EGRET Catalog and were included in determining the detection likelihood, flux, and spectra of those sources. In particular, five detected EGRET pulsars are found to have events above 10 GeV, and together they account for 37 events. A pulsar not included in the Third EGRET Catalog has 2 events, both with the same phase and in one peak of the lower-energy gamma-ray light-curve. Most of the remaining 1319 events appear to be diffuse Galactic and extragalactic radiation based on the similarity of the their spatial and energy distributions with the diffuse model and in the E〉100, MeV emission. No significant time clustering which would suggest a burst was detected.
    Keywords: Astrophysics
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  • 7
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    Identification and mapping of coal refuse banks and other targets in the anthracite region (1973)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: ERTS-1 MSS data covering parts of Pennsylvania's southern and eastern middle anthracite coal fields were studied to determine how well accumulations of coal refuse could be identified and mapped by computer analysis and processing. Spectral signatures of coal refuse targets were similar to water, but had higher reflectances in all channels. Relative reflectances were in the order 4 5 or = 6 7. Although no underflight photography was at hand to judge mapping success, correlation was made, with 1:24,000 scale U.S.G.S. maps dated 1947 and 1948. Coal refuse targets correlated well with existing maps.
    Keywords: GEOPHYSICS
    Type: PAPER-L24 , NASA. Goddard Space Flight Center Symp. on Significant Results obtained from the ERTS-1, Vol. 1, Sect. A and B; p 1067-1074
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  • 8
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    GLAST Large Area Telescope Multiwavelength Planning (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Because gamma-ray astrophysics depends in many ways on multiwavelength studies, the GLAST Large Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch of the observatory. Some of the high-priority needs include: (1) 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 flare measurements; (5) characterization of gamma-ray transients, including gamma ray bursts; (6) radio, optical, X-ray and TeV counterpart searches for unidentified gamma-ray sources. Work on the first three of these activities is needed before launch. The GLAST Large Area Telescope is an international effort, with U.S. funding provided by the Department of Energy and NASA.
    Keywords: Astrophysics
    Type: American Astronomical Society 207th Meeting; Jan 08, 2006 - Jan 12, 2006; Washington, DC; United States
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  • 9
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    GUST LAT Multiwavelength Planning (2004)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: Because gamma-ray astrophysics profits in powerful ways from multi-wavelength studies, the GLAST Large Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch. Many aspects of this program are of direct interest to observers using VERITAS and other atmospheric Cerenkov telescopes, whose capabilities complement those of GLAST. This talk with describe some of the current developmental concepts for GLAST LAT multiwavelength work, including release of data for transient sources, nearly-continuous monitoring of selected time-variable sources, pulsar timing, follow-on observations for source identification, coordinated blazar campaigns, and cross-calibration with other high-energy telescopes. Although few details are firm at this stage of preparation for GLAST, the LAT Collaboration looks forward to cooperation with a broad cross-section of the multiwave-length community. The GLAST Large Area Telescope is an international effort, with U.S. funding provided by the Department of Energy and NASA.
    Keywords: Astrophysics
    Type: High Energy Astrophysics Meeting; Sep 07, 2004 - Sep 11, 2004; New Orleans, LA; United States
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  • 10
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    IR excitation of contaminant water by oxygen for the space shuttle at low Earth orbit altitude (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: As the water outgas of a space shuttle passes through the rarefied atmosphere at orbital altitude, collisions occur between the gases with sufficient energy to excite infrared-active water molecules to various vibrational and rotational states. An infrared contaminant model (IR model) has been developed to study the shuttle-induced excitation and emission of water molecules outgassed from the space shuttle. The focus of the first application of the model is translation-to-vibration (T-V) energy transfer since estimates suggest that this process should dominate the production of vibrationally excited H2O under typical low Earth orbit conditions. Using the velocity and position distribution functions of interacting neutral gases obtained from a neutral gases interaction model, the spatial distributions of excitation and IR radiation from contaminant water are computed, and typical results are presented. Infrared spectral data (450 - 2500/cm), measured by the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS-1A) sensor on STS-39 (April 28 to May 6, 1991) at an altitude near 265 km, are used to test model predictions. The dependence of the radiant emission structure and brightness on outgassing rates and altitudes is discussed. The time history of the contaminant water outgassing rate is inferred for STS-39, and it is compared with the mass-spectrometer-based results for STS-4 (June 26 to July 4, 1982). Also, estimates of H2O column density at mission elapsed time (MET) 50 hours are compared for missions STS-2, STS-3, STS-4, and STS-39.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A10; p. 19,585-19,596
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