Magnetic field amplification in Tycho and other shell-type supernova remnants

By H. Völk, E. Berezhko, L. Ksenofontov. 2004

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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 Vs > 10 3 km s −1 , 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 π 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.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d33b7e802565ccfbf886cf65b65f424537e97b4a

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Citations in the corpus

Broad-band non-thermal emission from molecular clouds illuminated by cosmic rays from nearby supernova remnants (2009, background): “…for the gamma ray emission, comes from the observation of thin X-ray synchrotron filaments surrounding some SNRs (Bamba et al. 2003; Vink and Laming 2003; Völk et al. 2005) and of the rapid variability time scale of the synchrotron X–rays (Uchiyama et al. 2007; Uchiyama and Aharonian 2008).”
Strong evidence for hadron acceleration in Tycho’s supernova remnant (2011, background): “This interpretation allows us to estimate the magnetic field strength, which has to be as large as∼ 250µG inside the rim (Völk et al., 2005; Parizot et al., 2006).”
SPECTRUM OF GALACTIC COSMIC RAYS ACCELERATED IN SUPERNOVA REMNANTS (2010, methodology): “We employ results of Völk et al. (2005) in the analysis of Xray radiation from young SNRs and assume that magnetic energy density B2/8π downstream of the shock is 3.5 % of the ram pressure ρu2sh that determines the constant MA = 23.”
Cosmic ray acceleration and escape from supernova remnants (2013, background): “The fractional magnetic energy density can be chosen to match observation (Ptuskin et al 2010, Völk et al 2005).”
SIMULATIONS OF ION ACCELERATION AT NON-RELATIVISTIC SHOCKS. I. ACCELERATION EFFICIENCY (2013, background): “For instance, X-ray observations of young SNRs lead to inferred magnetic fields as large as a few hundreds µG, a factor of 50–100 larger than in the interstellar medium (see, e.g., Völk et al. 2005; Parizot et al. 2006, and references therein).”
A kinetic approach to cosmic-ray-induced streaming instability at supernova shocks (2008, background): “On the other hand, recent observations of the X-ray surface brightness of the rims of SNRs have shown thatδB/B ∼ 100− 1000 (see Völk et al. (2005) for a review of results), thereby renewing the interest in the mechanism of magnetic fild amplification and in establishing its saturation level.”
Analytical solutions for energy spectra of electrons accelerated by nonrelativistic shock-waves in shell type supernova remnants (2006, background): “This permits to explain the narrow X-ray filaments observed in SNRs and to estimate the magnetic field strength (see e.g. Berezhko et al. 2002, Völk et al. 2005).”
The origin of galactic cosmic rays (2013, unknown): “(2) X-ray spectrum and morphology strongly suggest that magnetic field amplification is taking place at SNR shocks (Völk et al. 2005), in virtually all young SNRs that we are aware of, with field strength of order few 100μG (Vink 2012).”
Cosmic-Ray Acceleration at the Forward Shock in Tycho’s Supernova Remnant: Evidence from Chandra X-Ray Observations (2005, background): “Völk et al. (2005) state that such amplification can happen if a significant portion of the cosmic rays are ions.”
NONTHERMAL RADIATION OF YOUNG SUPERNOVA REMNANTS: THE CASE OF RX J1713.7−3946 (2010, background): “For example, the energy of the magnetic field of about 3.5% of the dynamical pressure (Völk et al. 2005) and characteristic compression ratio of a modified shock σ = 6 correspond to MfA ≈ 23.”