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RISS 인기검색어
- 검색키워드
- 저자 : Edmon, Paul P. (검색결과 3 건)
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Non‐thermal radiation from Type Ia supernova remnants
Edmon, Paul P.,Kang, Hyesung,Jones, T. W.,Ma, Renyi Blackwell Publishing Ltd 2011 Monthly notices of the Royal Astronomical Society Vol.414 No.4
<P><B>ABSTRACT</B></P><P>We present calculations of expected continuum emissions from Sedov–Taylor phase Type Ia supernova remnants (SNRs), using the energy spectra of cosmic ray (CR) electrons and protons from non‐linear diffusive shock acceleration simulations. A new, general‐purpose radiative process code, <SMALL>cosmicp</SMALL>, was employed to calculate the radiation expected from CR electrons and protons and their secondary products. These radio, X‐ray and gamma‐ray emissions are generally consistent with current observations of Type Ia SNRs. The emissions from electrons in these models dominate the radio through X‐ray bands. Decays of π<SUP>0</SUP>s from p–p collisions mostly dominate the gamma‐ray range, although for a hot, low‐density ISM case (<I>n</I><SUB>ISM</SUB>= 0.003 cm<SUP>−3</SUP>), the pion decay contribution is reduced sufficiently to reveal the inverse Compton contribution to TeV gamma‐rays. In addition, we present simple scalings for the contributing emission processes to allow a crude exploration of model parameter space, enabling these results to be used more broadly. We also discuss the radial surface brightness profiles expected for these model SNRs in the X‐ray and gamma‐ray bands.</P>
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NONTHERMAL RADIATION FROM COSMIC-RAY MODIFIED SHOCKS
Kang, Hyesung,Edmon, Paul P.,Jones, T. W. IOP Publishing 2012 The Astrophysical journal Vol.745 No.2
<P>We calculate nonthermal radiation from cosmic-ray (CR) protons and electrons accelerated at CR modified plane and spherical shocks, using time-dependent, diffusive shock acceleration (DSA) simulations that include radiative losses of CR electrons. Strong non-relativistic shocks with physical parameters relevant for young supernova remnants (SNRs) are considered in both the plane-parallel and spherically symmetric geometries, and compared at times when their dynamical and CR properties are concordant. A thermal leakage injection model and a Bohm-like diffusion coefficient are adopted. After DSA energy gains balance radiative losses, the electron spectrum at the plane shock approaches a time-asymptotic spectrum with a super-exponential cutoff above the equilibrium momentum. The postshock electron spectrum cuts off at a progressively lower momentum downstream from the shock due to the energy losses. That results in the steepening of the volume integrated electron energy spectrum by one power of the particle energy. These features evolve toward lower energies in the spherical, SNR shocks. In a CR modified shock, pion decay gamma-ray emission reveals distinct signatures of nonlinear DSA due to the concave proton momentum spectrum. Although the electron momentum spectrum has a much weaker concavity, the synchrotron spectral slope at the shock may flatten by about 0.1-0.3 between radio and X-ray bands. The slope of the volume integrated emission spectrum behaves nonlinearly around the break frequency.</P>
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Kang, Hyesung,Jones, T. W.,Edmon, Paul P. IOP Publishing 2013 The Astrophysical journal Vol.777 No.1
<P>We explore nonlinear effects of wave-particle interactions on the diffusive shock acceleration (DSA) process in Type Ia-like supernova remnant (SNR) blast waves by implementing phenomenological models for magnetic field amplification (MFA), Alfvenic drift, and particle escape in time-dependent numerical simulations of nonlinear DSA. For typical SNR parameters, the cosmic-ray (CR) protons can be accelerated to PeV energies only if the region of amplified field ahead of the shock is extensive enough to contain the diffusion lengths of the particles of interest. Even with the help of Alfvenic drift, it remains somewhat challenging to construct a nonlinear DSA model for SNRs in which of the order of 10% of the supernova explosion energy is converted into CR energy and the magnetic field is amplified by a factor of 10 or so in the shock precursor, while, at the same time, the energy spectrum of PeV protons is steeper than E-2. To explore the influence of these physical effects on observed SNR emission, we also compute the resulting radio-to-gamma-ray spectra. Nonthermal emission spectra, especially in X-ray and gamma-ray bands, depend on the time-dependent evolution of the CR injection process, MFA, and particle escape, as well as the shock dynamic evolution. This result comes from the fact that the high-energy end of the CR spectrum is composed of particles that are injected in the very early stages of the blast wave evolution. Thus, it is crucial to better understand the plasma wave-particle interactions associated with collisionless shocks in detailed modeling of nonthermal radiation from SNRs.</P>
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