Author : 楊健恒
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Page : pages
File Size : 41,66 MB
Release : 2017
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Page : 34 pages
File Size : 38,50 MB
Release : 2011
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We present an analysis of the gamma-ray measurements by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region of the supernova remnant (SNR) Cygnus Loop (G74.0-8.5). We detect significant gamma-ray emission associated with the SNR in the energy band 0.2-100 GeV. The gamma-ray spectrum shows a break in the range 2-3 GeV. The gamma-ray luminosity is ≈ 1 x 1033 erg s−1 between 1-100 GeV, much lower than those of other GeV-emitting SNRs. The morphology is best represented by a ring shape, with inner/outer radii 0{sup o}.7 ± 0{sup o}.1 and 1{sup o}.6 ± 0{sup o}.1. Given the association among X-ray rims, H[alpha] filaments and gamma-ray emission, we argue that gamma rays originate in interactions between particles accelerated in the SNR and interstellar gas or radiation fields adjacent to the shock regions. The decay of neutral pions produced in nucleon-nucleon interactions between accelerated hadrons and interstellar gas provides a reasonable explanation for the gamma-ray spectrum.
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Page : 42 pages
File Size : 19,95 MB
Release : 2012
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We present a detailed analysis of the GeV gamma-ray emission toward the supernova remnant (SNR) G8.7-0.1 with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. An investigation of the relationship between G8.7-0.1 and the TeV unidentified source HESS J1804-216 provides us with an important clue on diffusion process of cosmic rays if particle acceleration operates in the SNR. The GeV gamma-ray emission is extended with most of the emission in positional coincidence with the SNR G8.7-0.1 and a lesser part located outside the western boundary of G8.7-0.1. The region of the gamma-ray emission overlaps spatially connected molecular clouds, implying a physical connection for the gamma-ray structure. The total gamma-ray spectrum measured with LAT from 200 MeV-100 GeV can be described by a broken power-law function with a break of 2.4 ± 0.6 (stat) ± 1.2 (sys) GeV, and photon indices of 2.10 ± 0.06 (stat) ± 0.10 (sys) below the break and 2.70 ± 0.12 (stat) ± 0.14 (sys) above the break. Given the spatial association among the gamma rays, the radio emission of G8.7-0.1, and the molecular clouds, the decay of p0s produced by particles accelerated in the SNR and hitting the molecular clouds naturally explains the GeV gamma-ray spectrum. We also find that the GeV morphology is not well represented by the TeV emission from HESS J1804-216 and that the spectrum in the GeV band is not consistent with the extrapolation of the TeV gamma-ray spectrum. The spectral index of the TeV emission is consistent with the particle spectral index predicted by a theory that assumes energy-dependent diffusion of particles accelerated in an SNR. We discuss the possibility that the TeV spectrum originates from the interaction of particles accelerated in G8.7-0.1 with molecular clouds, and we constrain the diffusion coefficient of the particles.
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Page : 5 pages
File Size : 40,17 MB
Release : 2011
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We report on gamma-ray observations of the supernova remnant (SNR) RX J0852.0-4622 with the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope. In the Fermi LAT data, we find a spatially extended source at the location of the SNR. The extension is consistent with the SNR size seen in other wavelengths such as X-rays and TeV gamma rays, leading to the identification of the gamma-ray source with the SNR. The spectrum is well described as a power law with a photon index of [Lambda] = 1.85 ± 0.06 (stat){sub -0.19}{sup +0.18} (sys), which smoothly connects to the H.E.S.S. spectrum in the TeV energy band. We discuss the gamma-ray emission mechanism based on multiwavelength data. The broadband data can be fit well by a model in which the gamma rays are of hadronic origin. We also consider a scenario with inverse Compton scattering of electrons as the emission mechanism of the gamma rays. Although the leptonic model predicts a harder spectrum in the Fermi LAT energy range, the model can fit the data considering the statistical and systematic errors.
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Page : 12 pages
File Size : 39,37 MB
Release : 2012
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We present an analysis of gamma-ray data obtained with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region around SNR S147 (G180.0-1.7). A spatially extended gamma-ray source detected in an energy range of 0.2-10 GeV is found to coincide with SNR S147. We confirm its spatial extension at>5? confidence level. The gamma-ray flux is (3.8 ± 0.6) x 10−8 photons cm−2 s−1, corresponding to a luminosity of 1.3 x 1034 (d/1.3 kpc)2 erg s−1 in this energy range. The gamma-ray emission exhibits a possible spatial correlation with prominent H? filaments of S147. There is no indication that the gamma-ray emission comes from the associated pulsar PSR J0538+2817. The gamma-ray spectrum integrated over the remnant is likely dominated by the decay of neutral? mesons produced through the proton-proton collisions in the filaments. Reacceleration of pre-existing CRs and subsequent adiabatic compression in the filaments is sufficient to provide the required energy density of high-energy protons.
Author : Kurt Weiler
Publisher : Springer
Page : 470 pages
File Size : 28,7 MB
Release : 2008-01-11
Category : Science
ISBN : 3540458638
Since the dawn of mankind, observers of the sky have wondered at the sudden appearance of new stars on the seemingly unchanging heavens and, for at least 2000 years, have recorded these phenomena in their annals and archives. Even in more modern times, since the discovery of SN1885A in S Andromeda which ?gured in the important “island universe” discussions of the 1920’s, the puzzle of supernovae (SNe) has played an important role in astrophysics. Only with the seminal work of Fritz Zwicky and Walter Baade in the 1930’s did we begin to understand the di?erences between novae and SNe and the importance of SNe as the fonts of energy for the interstellar medium and as drivers of chemical evolution in galaxies. As recently as the 1940’s and 1950’s the early days of radio astronomy were heavily in?uenced by the familiar names of Cassiopeia A and Taurus A, two young supernova remnants, and two Nobel prizes have been awarded for discovery and study of a related phenomenon, pulsars. In spite of the great age of the study of SNe, since at least the Chinese records of SN185and probably earlier, the ?eld is, in fact, very young having only attracted a large devoted following since the spectacular Type II SN1987A in the Large Magellanic Cloud, the ?rst naked-eye SN in more than 400 years.
Author : John Danziger
Publisher : Springer Science & Business Media
Page : 597 pages
File Size : 21,69 MB
Release : 2012-12-06
Category : Science
ISBN : 9400972318
IAU Symposium 101, Supernova Remnants and Their X-ray Emission, was held on the Island of San Giorgio, Venice, 30 August - 2 September 1982. It was co-sponsored by the National Research Council, Italy, the University of Padua, the Observatory of Padua, and the International Astronomical Union, and was hosted by the Cini Foundation. The contents of this volume show the wide range of disciplines that are involved in supernova remnant research. Many new results were presented, not only from the X-ray observations from the Einstein Observatory but also from observations at optical and radio wavelengths. This has led to the stimulation of theoretical work, much of which attempts to accommodate in a more unified way all of these observations. Research on supernova remnants of all ages was reported. Perhaps the most impressive part of all this work is the way in which observations at all wavelengths have extended well outside the Galaxy to other members of the Local Group and beyond. The Symposium was attended by scientists from 15 countries. Twenty five invited papers and sixty-eight shorter contributions were presented during the 4-day meeting. Thirty-three of these shorter contributions were presented in poster sessions. This volume contains almost all (89) of those contributions. They are followed by discussions which took place after each verbal presentation. Since the availability of the discussions was left to the individual contributors, they are not complete, but those contained in this volume convey some idea of the nature of the exchanges.
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Page : 17 pages
File Size : 19,36 MB
Release : 2011
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Author : Aurélien Philippe Bouvier
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Page : pages
File Size : 15,52 MB
Release : 2011
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The Fermi Gamma-ray Space Telescope recently celebrated its two-years anniversary in space. With the Large Area Telescope (LAT), its main instrument onboard, Fermi opened a new era in high-energy astrophysics and in particular for the study of Gamma-Ray Bursts (GRBs), which are short flashes of -rays associated with the brightest and most distant events ever observed in our universe after the Big Bang. My thesis work focused primarily on the observations of this phenomenon with the LAT (20 MeV - 300 GeV) and the Gamma-ray Burst Monitor (10 keV - 40 MeV) onboard the Fermi satellite. After describing the procedure used for detection and analysis of LAT GRBs, I will provide an overview of the temporal and spectral features observed during the prompt emission of these events after one year and a half of operation for Fermi. GRBs can also be used as a tool to probe interesting physics. My focus will be on the detection of very high energy photons (typically above 10 GeV) associated with LAT GRBs and which were used to set significant constraints both on a possible violation of Lorentz invariance - which postulates that all observers measure exactly the same speed of light in vacuum, independently of photon energy - and on the Optical-Ultraviolet extragalactic background light in the Universe.
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Page : 27 pages
File Size : 34,14 MB
Release : 2012
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