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          Institute: MPI für Kernphysik     Collection: Theoretical Astrophysics     Display Documents

ID: 201651.0, MPI für Kernphysik / Theoretical Astrophysics
Magnetic Field Amplification in Tycho and other Shell-type Supernova Remnants
Authors:Völk, Heinrich J.; Berezhko, Evgeny G.; Ksenofontov, Leonid T.
Date of Publication (YYYY-MM-DD):2005-04
Title of Journal:Astronomy & Astrophysics
Journal Abbrev.:A & A
Issue / Number:1
Start Page:229
End Page:240
Review Status:not specified
Audience:Experts Only
Abstract / Description:It is shown that amplification of the magnetic field in supernova remnants (SNRs) occurs in all six objects where morphological measurements are presently available in the hard X-ray continuum at several keV. For the three archetypical objects (SN 1006, Cas A and Tycho's SNR) to which nonlinear time-dependent acceleration theory has been successfully applied up to now, the global theoretical and the local observational field strengths agree very well, suggesting in addition that all young SNRs exhibit the amplification effect as a result of very efficient acceleration of nuclear cosmic rays (CRs) at the outer shock. Since this appears to be empirically the case, we may reverse the argument and consider field amplification as a measure of nuclear CR acceleration and it has indeed been argued that acceleration in the amplified fields allows the CR spectrum from SNRs to reach the knee in the spectrum or, in special objects, even beyond. The above results are furthermore used to investigate the time evolution of field amplification in young SNRs. Although the uncertainties in the data do not allow precise conclusions regarding this point, they rather clearly show that the ratio of the magnetic field energy density and the kinetic energy density of gas flow into the shock is of the order of a few percent if the shock speed is high enough V_s > 10^3 km/s, and this ratio remains nearly constant during the SNR evolution. The escape of the highest energy nuclear particles from their sources becomes progressively important with age, reducing also the cutoff in the \pi^0 -decay gamma-ray emission spectrum with time after the end of the sweep-up phase. Simultaneously the leptonic gamma-ray channels will gain in relative importance with increasing age of the sources.
External Publication Status:published
Document Type:Article
Affiliations:MPI für Kernphysik/Group H. J. Völk/Theoretical Astrophysics (F. Aharonian, J. Kirk)
External Affiliations:Institute of Cosmophysical Research and Aeronomy, 31 Lenin Ave., 677891 Yakutsk, Russia
Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan
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