9,096 research outputs found

    Propagation of Light Elements in the Galaxy

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    The origin and evolution of isotopes of the lightest elements H2, He3, Li, Be, B in the universe is a key problem in such fields as astrophysics of CR, Galactic evolution, non-thermal nucleosynthesis, and cosmological studies. One of the major sources of these species is spallation by CR nuclei in the interstellar medium. On the other hand, it is the B/C ratio in CR and Be10 abundance which are used to fix the propagation parameters and thus the spallation rate. We study the production and Galactic propagation of isotopes of elements Z<6 using the numerical propagation code GALPROP and updated production cross sections.Comment: 4 pages, 6 ps-figures, tsukuba.sty, to appear in the Proc. 28th International Cosmic Ray Conference (Tsukuba, Japan 2003). More details can be found at http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm

    Diffractive Interaction and Scaling Violation in pp->pi^0 Interaction and GeV Excess in Galactic Diffuse Gamma-Ray Spectrum of EGRET

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    We present here a new calculation of the gamma-ray spectrum from pp->pi^0 in the Galactic ridge environment. The calculation includes the diffractive pp interaction and incorporates the Feynman scaling violation for the first time. Galactic diffuse gamma-rays come, predominantly, from pi^0->gamma gamma in the sub-GeV to multi-GeV range. Hunter et al. found, however, an excess in the GeV range ("GeV Excess") in the EGRET Galactic diffuse spectrum above the prediction based on experimental pp->pi^0 cross-sections and the Feynman scaling hypothesis. We show, in this work, that the diffractive process makes the gamma-ray spectrum harder than the incident proton spectrum by ~0.05 in power-law index, and, that the scaling violation produces 30-80% more pi^0 than the scaling model for incident proton energies above 100GeV. Combination of the two can explain about a half of the "GeV Excess" with the local cosmic proton (power-law index ~2.7). The excess can be fully explained if the proton spectral index in the Galactic ridge is a little harder (~0.2 in power-law index) than the local spectrum. Given also in the paper is that the diffractive process enhances e^+ over e^- and the scaling violation gives 50-100% higher p-bar yield than without the violation, both in the multi-GeV range.Comment: 35 pages, 11 figures, to appear in Astrophysical Journa

    EGRET Observations of the Diffuse Gamma-Ray Emission in Orion: Analysis Through Cycle 6

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    We present a study of the high-energy diffuse emission observed toward Orion by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory. The total exposure by EGRET in this region has increased by more than a factor of two since a previous study. A simple model for the diffuse emission adequately fits the data; no significant point sources are detected in the region studied (l=195∘l = 195^\circ to 220∘220^\circ and b=−25∘to−10∘b = -25^\circ to -10^\circ) in either the composite dataset or in two separate groups of EGRET viewing periods considered. The gamma-ray emissivity in Orion is found to be (1.65±0.11)×10−26ssr−1(1.65 \pm 0.11) \times 10^{-26} {s sr}^{-1} for E > 100 MeV, and the differential emissivity is well-described as a combination of contributions from cosmic-ray electrons and protons with approximately the local density. The molecular mass calibrating ratio is N(H2)/WCO=(1.35±0.15)×1020cm−2(Kkm/s)−1N(H_2)/W_{CO} = (1.35 \pm 0.15) \times 10^{20} cm^{-2} (K km/s)^{-1}.Comment: 16 pages, including 5 figures. 3 Tables as three separate files. Latex document, needs AASTEX style files. Accepted for publication in Ap

    Caring for our country: wind erosion extent and severity maps for Australia, final report

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    The Wind Erosion Extent and Severity Maps (WEESMAP) project for Australia has been completed. As a result of the project significant improvements were made to both the soil and vegetation input data. These improvements include: • A new dynamic erodibility mask was created for the model,based on Fractional Cover Index (FCI) of Guerschman et al. (2009). • Increasing the soil descriptions available from 12 to 29 soils. • Replacing LAI GIS layer with the MODIS LAI layer, which no longer uses empirical relationships developed for AVHRR NDVI product. • The model was extend to a 10km resolution for the whole of the continent. Statistical comparison of the CEMSYS model before (Version 5) and after the soil/vegetation improvements (Version 6) shows that the model over estimated daily dust concentrations at 26 of the DustWatch nodes in 2009 by approximately 3 fold for V5 and underestimated it by 0.6 for V6. The mean error between modelled and observed dust levels was reduced for V6 (0.0227 to 0.0084). Finally V6 explained twice the level of variability in the observed data compared to V5 (0.2292 to 0.3956). Given the result was comparing 26 stations over 365 days, V6 appears extremely robust over the yearly period. In addition, the time series of available data was extended significantly. At the end of the project data the following data is available: • Version 650 km data is available from March2000–June2012. • Version 510 km dat is available for NSW/Victoria from February2000–June2012. • Version 610 km data is available nationally for 2002,2008,and 2009. Finally several other coding improvements were made to the model to increase performance. Consequently, it is now possible to produce 50 km and 10 km maps within 10 days of the external MODIS and Atmospheric data becoming available. This means it is now possible to use the CEMSYS in monthly reporting products

    SPI Measurements of Galactic 26Al

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    The precision measurement of the 1809 keV gamma-ray line from Galactic 26^{26}Al is one of the goals of the SPI spectrometer on INTEGRAL with its Ge detector camera. We aim for determination of the detailed shape of this gamma-ray line, and its variation for different source regions along the plane of the Galaxy. Data from the first part of the core program observations of the first mission year have been inspected. A clear detection of the \Al line at about 5--7 σ\sigma significance demonstrates that SPI will deepen \Al studies. The line intensity is consistent with expectations from previous experiments, and the line appears narrower than the 5.4 keV FWHM reported by GRIS, more consistent with RHESSI's recent value. Only preliminary statements can be made at this time, however, due to the multi-component background underlying the signal at \about 40 times higher intensity than the signal from Galactic 26^{26}Al.Comment: 5 pages, 8 figures; accepted for publication in A&A (special INTEGRAL volume

    Development of a theory of the spectral reflectance of minerals, part 2

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    Theory of diffuse reflectance of particulate media including garnet, glass, corundum powders, and mixture
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