Nonlinear Diffusive Shock Acceleration with Magnetic Field Amplification

Vladimirov, Andrey; Ellison, Donald C.; Bykov, A. M.

doi:10.1086/508154

Cited by 124 publications

(165 citation statements)

References 53 publications

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“…A crucial ingredient is the velocity of the scattering centers, which is generally neglected with respect to the shock speed, but could be significantly enhanced when the magnetic field is amplified (Vladimirov et al 2006;Caprioli et al 2009a;Zirakasvhili & Ptuskin 2008). When this occurs, the total compression factor felt by accelerated particles may be reduced appreciably and, in turn, the spectra of accelerated particles may be considerably softer.…”

Section: Introductionmentioning

confidence: 99%

Strong evidence for hadron acceleration in Tycho’s supernova remnant

Morlino

Caprioli

2012

A&A

299

313

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Context. Very recent gamma-ray observations of G120.1+1.4 (Tycho's) supernova remnant (SNR) by Fermi-LAT and VERITAS have provided new fundamental pieces of information for understanding particle acceleration and nonthermal emission in SNRs. Aims. We want to outline a coherent description of Tycho's properties in terms of SNR evolution, shock hydrodynamics, and multiwavelength emission by accounting for particle acceleration at the forward shock via first-order Fermi mechanism. Methods. We adopt here a quick and reliable semi-analytical approach to nonlinear diffusive shock acceleration. It includes magnetic field amplification due to resonant streaming instability and the dynamical backreaction on the shock of both cosmic rays (CRs) and self-generated magnetic turbulence. Results. We find that Tycho's forward shock accelerates protons up to at least 500 TeV, channelling into CRs about 10% of its kinetic energy. Moreover, the CR-induced streaming instability is consistent with all the observational evidence of very efficient magnetic field amplification (up to ∼300 μG). In such a strong magnetic field, the velocity of the Alfvén waves scattering CRs in the upstream is expected to be enhanced and to make accelerated particles feel an effective compression factor lower than 4, in turn leading to an energy spectrum steeper than the standard prediction ∝E −2 . This effect is crucial for explaining GeV-to-TeV gamma-ray spectrum as the result of neutral pions decay produced in nuclear collisions between accelerated nuclei and the background gas. Conclusions. The self-consistency of such hadronic scenario, along with the inability of the concurrent leptonic mechanism (inverse Compton scattering of relativistic electrons on several photon backgrounds) to reproduce both the shape and the normalization of the detected gamma-ray emission, represents the first clear and direct radiative evidence that hadron acceleration occurs efficiently in young Galactic SNRs.

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Section: Introductionmentioning

confidence: 99%

Strong evidence for hadron acceleration in Tycho’s supernova remnant

Morlino

Caprioli

2012

A&A

299

313

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“…and how it evolves downstream (does it decrease and, if so, at what rate?). While theoretical studies suggest that the magnetic field (specifically its turbulent component) may be significantly amplified at the shock (Lucek & Bell 2000;Bell & Lucek 2001;Vladimirov et al 2006), it remains uncertain whether it is quickly damped on a timescale shorter than that of the energy losses of electrons (Pohl et al 2005) or is simply carried along by the plasma flow in the downstream region. As we show below, these two situations lead to different predictions about the spectral variations of the X-ray synchrotron emission and the relative radio and X-ray synchrotron morphology at the blast wave.…”

Section: Introductionmentioning

confidence: 99%

The Blast Wave of Tycho’s Supernova Remnant

Cassam-Chenaï

Hughes

Ballet

et al. 2007

ApJ

141

183

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We use the Chandra X-Ray Observatory to study the region in the Tycho supernova remnant between the blast wave and the shocked ejecta interface or contact discontinuity. This zone contains all the history of the shock-heated gas and cosmic-ray acceleration in the remnant. We present for the first time evidence for significant spatial variations of the X-ray synchrotron emission in the form of spectral steepening from a photon index of $2.6 right at the blast wave to a value of $3.0 several arcseconds behind. We interpret this result along with the profiles of radio and X-ray intensity using a self-similar hydrodynamical model including cosmic-ray back-reaction that accounts for the observed ratio of radii between the blast wave and contact discontinuity. Two different assumptions were made about the postshock magnetic field evolution: one where the magnetic field (amplified at the shock) is simply carried by the plasma flow and remains relatively high in the postshock region (synchrotron losses limited rim case), and another where the amplified magnetic field is rapidly damped behind the blast wave (magnetic damping case). Both cases fairly well describe the X-ray data; however, both fail to explain the observed radio profile. The projected synchrotron emission leaves little room for the presence of thermal emission from the shocked ambient medium. This can only be explained if the preshock ambient medium density in the vicinity of the Tycho supernova remnant is below 0.6 cm À3 .

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“…Baring et al (1995) also used the stationary Monte Carlo method for simulating the oblique interplanetary shocks, and the calculated results are a good fit to the observed data. There are many works that use the Monte Carlo method: Ellison et al (1996), Ellison & Double (2002), Vladimirov et al (2006Vladimirov et al ( , 2008, and others.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo simulations of a diffusive shock with multiple scattering angular distributions

Wang

Yan

2011

A&A

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Aims. We independently develop a simulation code following the previous dynamical Monte Carlo simulation of the diffusive shock acceleration under the isotropic scattering law during the scattering process, and the same results are obtained. Methods. Since the same results test the validity of the dynamical Monte Carlo method for simulating a collisionless shock, we extend the simulation toward including an anisotropic scattering law for further developing this dynamical Monte Carlo simulation. Under this extended anisotropic scattering law, a Gaussian distribution function is used to describe the variation of scattering angles in the particle's local frame. Results. As a result, we obtain a series of different shock structures and evolutions in terms of the standard deviation values of the given Gaussian scattering angular distributions. Conclusions. We find that the total energy spectral index increases as the standard deviation value of the scattering angular distribution increases, but the subshock's energy spectral index decreases as the standard deviation value of the scattering angular distribution increases.

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Nonlinear Diffusive Shock Acceleration with Magnetic Field Amplification

Cited by 124 publications

References 53 publications

Strong evidence for hadron acceleration in Tycho’s supernova remnant

Strong evidence for hadron acceleration in Tycho’s supernova remnant

The Blast Wave of Tycho’s Supernova Remnant

Monte Carlo simulations of a diffusive shock with multiple scattering angular distributions

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