Turbulent Amplification of a Magnetic Field Driven by the Dynamo Effect at Rippled Shocks

Fraschetti, Federico

doi:10.1088/0004-637x/770/2/84

Cited by 59 publications

(68 citation statements)

References 54 publications

(87 reference statements)

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“…In this paper we show for the first time that the overdensity clumps within the expanding plasma of Cassiopeia A, once crossed by the reflection inward shock, lead to the [4.2 − 6] keV flux increase via magnetic field amplification through vorticity generation, as calculated in Fraschetti [7]. Such a process was first identified via two-dimensional magnetohydrodynamic (MHD) numerical simulations in Giacalone and Jokipii [8] and also investigated by several teams, including Inoue et al [9].…”

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confidence: 55%

Vortical Amplification of the Magnetic Field at an Inward Shock of Supernova Remnant Cassiopeia A

et al. 2018

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We present an interpretation of the time variability of the x-ray flux recently reported from a multiepoch campaign of 15 years of observations of the supernova remnant Cassiopeia A by Chandra. We show for the first time quantitatively that the [4.2-6] keV nonthermal flux increase up to 50% traces the growth of the magnetic field due to a vortical amplification mechanism at a reflection inward shock colliding with inner overdensities. The fast synchrotron cooling as compared with shock-acceleration time scale qualitatively supports the flux decrease.

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confidence: 55%

Vortical Amplification of the Magnetic Field at an Inward Shock of Supernova Remnant Cassiopeia A

et al. 2018

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“…More generally, turbulence is believed to be an efficient agent to amplify magnetic fields via the turbulent dynamo (Kazantsev 1968;Kulsrud & Anderson 1992), which has also been invoked for explaining both the preshock (Beresnyak, Jones, & Lazarian 2009, hereafter BJL09;Drury & Downes 2012;del Valle et al 2016) and postshock (Balsara et al 2001;Giacalone & Jokipii 2007;Inoue et al 2009;Guo et al 2012;Fraschetti 2013;Ji et al 2016) magnetic fields. As turbulence is induced by the interaction between SNR shocks and interstellar turbulent density fluctuations, the turbulent dynamo is inevitable in SNRs with the turbulent kinetic energy dominating over the pre-existing magnetic energy.…”

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confidence: 99%

Magnetic Field Amplification in Supernova Remnants

Lazarían¹

2017

ApJ

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Based on the new findings on the turbulent dynamo in , we examine the magnetic field amplification in the context of supernova remnants. Due to the strong ion-neutral collisional damping in the weakly ionized interstellar medium, the dynamo in the preshock turbulence remains in the damping kinematic regime, which leads to a linear-in-time growth of the magnetic field strength. The resultant magnetic field structure enables effective diffusion upstream and shock acceleration of cosmic rays to energies above the "knee". Differently, the nonlinear dynamo in the postshock turbulence leads to a linear-in-time growth of the magnetic energy due to the turbulent magnetic diffusion. Given a weak initial field strength in the postshock region, the magnetic field saturates at a significant distance from the shock front as a result of the inefficiency of the nonlinear dynamo. This result is in a good agreement with existing numerical simulations and well explains the X-ray spots detected far behind the shock front.

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“…As a turbulent dynamo effect, it is known that magnetic field can be amplified by astrophysical shocks beyond simple shock compression. This has been proved both numerically [7] and analytically [8], and has been applied to explain observations of supernovae remnants (SNRs) [9] and γ-ray bursts (GRBs) [10]. If this kind of amplification is also at work in the shocks in the relativistic jets which presumably cause the blazar flares, it can be expected to explain the orphan optical flares.…”

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confidence: 88%

Magnetic Field Amplification and Blazar Flares

Chen

Chatterjee

Fossati

et al. 2013

EPJ Web of Conferences

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Abstract. Recent multiwavelength observations of PKS 0208-512 by SMARTS, Fermi, and Swift revealed that γ-ray and optical light curves of this flat spectrum radio quasars are highly correlated, but with an exception of one large optical flare having no corresponding gamma-ray activity or even detection. On the other hand, recent advances in SNRs observations and plasma simulations both reveal that magnetic field downstream of astrophysical shocks can be largely amplified beyond simple shock compression. These amplifications, along with their associated particle acceleration, might contribute to blazar flares, including the peculiar flare of PKS 0208-512. Using our time dependent multizone blazar emission code, we evaluate several scenarios that may represent such phenomena. This code combines Monte Carlo method that tracks the radiative processes including inverse Compton scattering, and Fokker-Planck equation that follows the cooling and acceleration of particles. It is a comprehensive time dependent code that fully takes into account the light travel time effects. In this study, both the changes of the magnetic field and acceleration efficiency are explored as the cause of blazar flares. Under these assumption, synchrotron self-Compton and external Compton scenarios produce distinct features that favor the external Compton scenario. The optical flares with/without gamma-ray counterparts can be explained by different allocations of energy between the magnetization and particle acceleration, which in turn can be affected by the relative orientation between the magnetic field and the shock flow. We compare the details of the observations and simulation, and highlight what implications this study has on our understanding of relativistic jets.

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Turbulent Amplification of a Magnetic Field Driven by the Dynamo Effect at Rippled Shocks

Cited by 59 publications

References 54 publications

Vortical Amplification of the Magnetic Field at an Inward Shock of Supernova Remnant Cassiopeia A

Vortical Amplification of the Magnetic Field at an Inward Shock of Supernova Remnant Cassiopeia A

Magnetic Field Amplification in Supernova Remnants

Magnetic Field Amplification and Blazar Flares

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