Mirror Acceleration of Cosmic Rays in a High-β Medium

Lazarian, Alex; Xu, Siyao

doi:10.3847/1538-4357/acea5c

Cited by 6 publications

(1 citation statement)

References 67 publications

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“…A fraction of the turbulent energy can be converted into nonthermal components such as cosmic rays and the magnetic field through stochastic acceleration and a turbulent dynamo. Turbulence in astrophysical environments may accelerate particles via different mechanisms, including resonant and nonresonant ones (e.g., Ptuskin 1988;Schlickeiser & Miller 1998;Cho & Lazarian 2006;Brunetti & Lazarian 2007;Lynn et al 2014;Lemoine 2021;Bustard & Oh 2022;Lazarian & Xu 2023). Recent MHD simulations of galaxy clusters suggested that the turbulence in the ICM is dominated by the solenoidal (incompressible) mode (e.g., Miniati 2015;Vazza et al 2017).…”

Section: Cr Reacceleration and Field Amplification By Solenoidal Turb...mentioning

confidence: 99%

Efficiency of Turbulent Reacceleration by Solenoidal Turbulence and Its Application to the Origin of Radio Megahalos in Cluster Outskirts

Nishiwaki,

Brunetti,

Vazza

et al. 2024

ApJ

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Recent radio observations with the Low Frequency Array (LOFAR) discovered diffuse emission extending beyond the scale of classical radio halos. The presence of such megahalos indicates that the amplification of the magnetic field and acceleration of relativistic particles are working in the cluster outskirts, presumably due to the combination of shocks and turbulence that dissipate energy in these regions. Cosmological magnetohydrodynamical (MHD) simulations of galaxy clusters suggest that solenoidal turbulence has a significant energy budget in the outskirts of galaxy clusters. In this paper, we explore the possibility that this turbulence contributes to the emission observed in megahalos through second-order Fermi acceleration of relativistic particles and magnetic field amplification by the dynamo. We focus on the case of A2255 and find that this scenario can explain the basic properties of the diffuse emission component that is observed under assumptions that are used in previous literature. More specifically, we conduct a numerical follow-up, solving the Fokker–Planck equation by using a snapshot of an MHD simulation and deducing the synchrotron brightness integrated along the lines of sight. We find that a volume-filling emission, ranging between 30% and almost 100% of the projected area, depending on our assumptions on the particle diffusion and transport, can be detected at LOFAR sensitivities. Assuming a magnetic field B ∼ 0.2 μG, as derived from a dynamo model applied to the emitting region, we find that the observed brightness can be matched when ∼1% of the solenoidal turbulent energy flux is channeled into particle acceleration.

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Section: Cr Reacceleration and Field Amplification By Solenoidal Turb...mentioning

confidence: 99%

Efficiency of Turbulent Reacceleration by Solenoidal Turbulence and Its Application to the Origin of Radio Megahalos in Cluster Outskirts

Nishiwaki,

Brunetti,

Vazza

et al. 2024

ApJ

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A fluid approach to cosmic-ray modified shocks

Ramzan,

Qazi,

Salarzai

et al. 2024

Advances in Space Research

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Strong turbulence and magnetic coherent structures in the interstellar medium

Ntormousi,

Vlahos,

Konstantinou

et al. 2024

A&A

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Magnetic turbulence is classified as weak or strong based on the relative amplitude of the magnetic field fluctuations compared to the mean field. These two classes have different energy transport properties. The purpose of this study is to analyze turbulence in the interstellar medium (ISM) based on this classification. Specifically, we examined the ISM of simulated galaxies to detect evidence of strong magnetic turbulence and provide statistics on the associated magnetic coherent structures (MCoSs), such as current sheets, that arise in this context. We analyzed magnetohydrodynamic galaxy simulations with different initial magnetic field structures (either completely ordered or completely random) and recorded statistics on the magnetic field fluctuations ($ B/B_0$) and the MCoSs, which are defined here as regions where the current density surpasses a certain threshold. We also studied the MCoS sizes and kinematics. The magnetic field disturbances in both models follow a log-normal distribution, peaking at values close to unity; this distribution turns into a power law at large values ($ B/B_0 > 1$), which is consistent with strong magnetic turbulence The current densities are widely distributed, with non-power-law deviations from a log-normal at the largest values. These deviating values of the current density define MCoSs. We find that, in both models, MCoSs are fractally distributed in space, with a typical volume-filling factor of about 10 percent, and tend to coincide with peaks of star formation density. Their fractal dimension is close to unity on sub-kiloparsec scales, and between 2 and 3 on larger scales. These values are consistent with MCoSs having a sheet-like or filament-like morphology. Our work challenges the prevailing paradigm of weak magnetic turbulence in the ISM by demonstrating that strong magnetic disturbances can occur even when the initial magnetic field is completely ordered. This strong magnetic turbulence arises self-consistently from differential rotation and supernova feedback. Our findings provide a foundation for a magnetic turbulence description of the galactic ISM that includes strong fluctuations of the magnetic field.

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Mirror Acceleration of Cosmic Rays in a High-β Medium

Cited by 6 publications

References 67 publications

Efficiency of Turbulent Reacceleration by Solenoidal Turbulence and Its Application to the Origin of Radio Megahalos in Cluster Outskirts

Efficiency of Turbulent Reacceleration by Solenoidal Turbulence and Its Application to the Origin of Radio Megahalos in Cluster Outskirts

A fluid approach to cosmic-ray modified shocks

Strong turbulence and magnetic coherent structures in the interstellar medium

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