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  • 11
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    A Statistical Approach to Recognizing Source Classes for Unassociated Sources in the First FERMI-LAT Catalog (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Fermi Large Area Telescope (LAT) First Source Catalog (1FGL) provided spatial, spectral, and temporal properties for a large number of gamma -ray sources using a uniform analysis method. After correlating with the mostcomplete catalogs of source types known to emit gamma rays, 630 of these sources are "unassociated" (i.e., have no obvious counterparts at other wavelengths). Here, we employ two statistical analyses of the primary gamma-ray characteristics for these unassociated sources in an effort to correlate their gamma-ray properties with the active galactic nucleus (AGN) and pulsar populations in 1FGL. Based on the correlation results, we classify 221 AGN-like and 134 pulsar-like sources in the 1FGL unassociated sources. The results of these source "classifications" appear to match the expected source distributions, especially at high Galactic latitudes. While useful for planning future multiwavelength follow-up observations, these analyses use limited inputs, and their predictions should not be considered equivalent to "probable source classes" for these sources. We discuss multiwavelength results and catalog cross-correlations to date, and provide new source associations for 229 Fermi-LAT sources that had no association listed in the 1FGL catalog. By validating the source classifications against these new associations, we find that the new association matches the predicted source class in approximately 80% of the sources.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN9282 , The Astrophysical Journal; 753; 1; 83
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  • 12
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    FERMI Observations of Gamma -Ray Emission From the Moon (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We report on the detection of high-energy -ray emission from the Moon during the first 24 months of observations by the Fermi Large Area Telescope (LAT). This emission comes from particle cascades produced by cosmicray (CR) nuclei and electrons interacting with the lunar surface. The differential spectrum of the Moon is soft and can be described as a log-parabolic function with an effective cutoff at 2-3 GeV, while the average integral flux measured with the LAT from the beginning of observations in 2008 August to the end of 2010 August is F(greater than100 MeV) = (1.04 plus or minus 0.01 [statistical error] plus or minus 0.1 [systematic error]) 10(sup 6) cm(sup 2) s(sup 1). This flux is about a factor 2-3 higher than that observed between 1991 and 1994 by the EGRET experiment on board the Compton Gamma Ray Observatory, F(greater than100 MeV)510(sup 7) cm(sup 2) s(sup 1), when solar activity was relatively high. The higher gamma -ray flux measured by Fermi is consistent with the deep solar minimum conditions during the first 24 months of the mission, which reduced effects of heliospheric modulation, and thus increased the heliospheric flux of Galactic CRs. A detailed comparison of the light curve with McMurdo Neutron Monitor rates suggests a correlation of the trends. The Moon and the Sun are so far the only known bright emitters of gamma-rays with fast celestial motion. Their paths across the sky are projected onto the Galactic center and high Galactic latitudes as well as onto other areas crowded with high-energy gamma-ray sources. Analysis of the lunar and solar emission may thus be important for studies of weak and transient sources near the ecliptic.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN9743 , Astrophysical Journal; 758; 2; 140
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  • 13
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    ANTARES Constrains a Blazar Origin of Two IceCube PeV Neutrino Events (2015)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Context. The source(s) of the neutrino excess reported by the IceCube Collaboration is unknown. The TANAMI Collaboration recently reported on the multiwavelength emission of six bright, variable blazars which are positionally coincident with two of the most energetic IceCube events. Objects like these are prime candidates to be the source of the highest-energy cosmic rays, and thus of associated neutrino emission. Aims. We present an analysis of neutrino emission from the six blazars using observations with the ANTARES neutrino telescope. Methods. The standard methods of the ANTARES candidate list search are applied to six years of data to search for an excess of muons - and hence their neutrino progenitors - from the directions of the six blazars described by the TANAMI Collaboration, and which are possibly associated with two IceCube events. Monte Carlo simulations of the detector response to both signal and background particle fluxes are used to estimate the sensitivity of this analysis for di erent possible source neutrino spectra. A maximum-likelihood approach, using the reconstructed energies and arrival directions of through-going muons, is used to identify events with properties consistent with a blazar origin. Results. Both blazars predicted to be the most neutrino-bright in the TANAMI sample (1653-329 and 1714-336) have a signal flux fitted by the likelihood analysis corresponding to approximately one event. This observation is consistent with the blazar-origin hypothesis of the IceCube event IC 14 for a broad range of blazar spectra, although an atmospheric origin cannot be excluded. No ANTARES events are observed from any of the other four blazars, including the three associated with IceCube event IC20. This excludes at a 90% confidence level the possibility that this event was produced by these blazars unless the neutrino spectrum is flatter than -2.4.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN34645 , Astronomy & Astrophysics (e-ISSN 1432-0746); 576; L8
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  • 14
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    Inferred Cosmic-Ray Spectrum from Fermi-LAT Gamma-Ray Observations of the Earths Limb (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Recent accurate measurements of cosmic-ray (CR) species by ATIC-2, CREAM, and PAMELA reveal an unexpected hardening in the proton and He spectra above a few hundred GeV, a gradual softening of the spectra just below a few hundred GeV, and a harder spectrum of He compared to that of protons. These newly-discovered features may offer a clue to the origin of high-energy CRs. We use the Fermi Large Area Telescope observations of the -ray emission from the Earth's limb for an indirect measurement of the local spectrum of CR protons in the energy range approx. 90 GeV-6 TeV (derived from a photon energy range 15 GeV-1 TeV). Our analysis shows that single power law and broken power law spectra fit the data equally well and yield a proton spectrum with index 2.68 +/- 0.04 and 2.61 +/- 0.08 above approx. 200 GeV, respectively.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN23087
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  • 15
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    The X-Ray Counterpart to LAT PSR J2021+4026 and Its Interesting Spectrum (2011)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: We report on the likely identification of the X-ray counterpart to LAT PSR J2021+4026, using the Chandra X-Ray Observatory ACIS-S3 and timing analysis of Large Area telescope (LAT) data from the Fermi satellite. The X-ray source that lies closest (10 arcsec) to the position determined from the Fermi-LAT timing solution has no cataloged infrared-to-visible counterpart and we have set an upper limit to its optical I and R band emission. The source exhibits a X-ray spectrum which is different when compared to Geminga and CTA 1, and this may have implications for the evolutionary track of radio-quiet gamma-ray pulsars.
    Keywords: Astrophysics
    Type: M11-1059 , 2011 Meeting of the High Energy Astrophysics Division; Sep 07, 2011 - Sep 10, 2011; Newport News, RI; United States
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  • 16
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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: Identification and mapping of coal refuse banks and other targets in anthracite region of Pennsylvania
    Keywords: GEOPHYSICS
    Type: E73-10222 , PAPER-L24 , NASA. Goddard Space Flight Center Land Use and Mapping; p 117
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  • 17
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    Mapping of anthracite refuse (1973)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: There are no author-identified significant results in this report.
    Keywords: GEOPHYSICS
    Type: E73-11107 , NASA-CR-135575 , ORSER-SSEL-TR-20-73
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  • 18
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    Extreme Blazars Studied with Fermi-Lat and Suzaku: 1ES 0347-121 and Blazar Candidate HESS J1943+213 (2014)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We report on our study of high-energy properties of two peculiar TeV emitters: the "extreme blazar" 1ES 0347-121 and the "extreme blazar candidate" HESS J1943+213 located near the Galactic plane. Both objects are characterized by quiescent synchrotron emission with flat spectra extending up to the hard X-ray range, and both were reported to be missing GeV (gigaelectronvolt) counterparts in the Fermi Large Area Telescope (LAT) two-year Source Catalog. We analyze a 4.5 year accumulation of the Fermi-LAT data, resulting in the detection of 1ES 0347-121 in the GeV band, as well as in improved upper limits for HESS J1943+213. We also present the analysis results of newly acquired Suzaku data for HESS J1943+213. The X-ray spectrum is well represented by a single power law extending up to 25 keV (kiloelectronvolts) with photon index 2.00 plus or minus 0.02 and a moderate absorption in excess of the Galactic value, which is in agreement with previous X-ray observations. No short-term X-ray variability was found over the 80 kilosecond duration of the Suzaku exposure. Under the blazar hypothesis, we modeled the spectral energy distributions of 1ES 0347-121 and HESS J1943+213, and we derived constraints on the intergalactic magnetic field strength and source energetics. We conclude that although the classification of HESS J1943+213 has not yet been determined, the blazar hypothesis remains the most plausible option since, in particular, the broadband spectra of the two analyzed sources along with the source model parameters closely resemble each other, and the newly available Wide-field Infrared Survey Explorer (WISE) and UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey data for HESS J1943+213 are consistent with the presence of an elliptical host at the distance of approximately 600 Mpc (megaparsecs).
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN21789 , Astrophysical Journal (ISSN 2041-8205) (e-ISSN 2041-8213); 787; 2; 155
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  • 19
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    Swift and GLAST Cooperative Efforts (2007)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: Because gamma-ray astrophysics depends in many ways on multiwavelength studies, the Gamma-ray Large Area Space Telescope (GLAST) instrument teams are eagerly anticipating coordinated observations with the Swift observatory. Swift and GLAST combined cover most of twelve orders of magnitude in the electromagnetic spectrum, offering numerous opportunities for cooperation. Three of the high-priority interests are: (1) gamma-ray burst studies; (2) broad-spectrum studies of blazars in both quiescent and flaring states; and (3) identification and detailed study of unidentified gamma-ray sources.
    Keywords: Astrophysics
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  • 20
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    Pulsar Simulations for the Fermi Large Area Telescope (2009)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Pulsars are among the prime targets for the Large Area Telescope (LAT) aboard the recently launched Fermi observatory. The LAT will study the gamma-ray Universe between 20 MeV and 300 GeV with unprecedented detail. Increasing numbers of gamma-ray pulsars are being firmly identified, yet their emission mechanisms are far from being understood. To better investigate and exploit the tAT capabilities for pulsar science. a set of new detailed pulsar simulation tools have been developed within the LAT collaboration. The structure of the pulsar simulator package (PulsarSpeccrum) is presented here. Starting from photon distributions in energy and phase obtained from theoretical calculations or phenomenological considerations, gamma-rays are generated and their arrival times at the spacecraft are determined by taking Into account effects such as barycentric effects and timing noise. Pulsars in binary systems also can be simulated given orbital parameters. We present how simulations can be used for generating a realistic set of gamma rays as observed by the LAT, focusing on some case studies that show the performance of the LAT for pulsar observations.
    Keywords: Astrophysics
    Type: GSFC.JA.6890.2012 , Astroparticle Physics; 32; 1; 1-9
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