Non-linear diffusive shock acceleration: A recipe for injection of electrons

Арбутина, Б.; Zeković, Vladimir

doi:10.1016/j.astropartphys.2020.102546

Cited by 18 publications

(30 citation statements)

References 81 publications

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“…The presence of high-energy protons or electrons is not only dependent on their maximum energies (see Section C.1). Differences in the injection process of electrons and hadrons into the acceleration mechanism (see [84] and references therein) can cause preferential dominant acceleration of one or the other type of particles.…”

Section: C6 Proton-lepton Modelmentioning

confidence: 99%

Proton acceleration in thermonuclear nova explosions revealed by gamma rays

et al. 2022

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Section: C6 Proton-lepton Modelmentioning

confidence: 99%

Proton acceleration in thermonuclear nova explosions revealed by gamma rays

et al. 2022

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“…(34) which requires 𝑞 𝑘 1 to explain the observed Δ𝑠 ep 0.3. In our opinion, however, results from Arbutina & Zeković (2021) deserve further investigations because their simulations are limited to high shock speed (∼ 𝑐/3) in a regime where thermal electrons are already relativistic, a condition far from being realized in typical SNR shocks.…”

Section: Results For Time Dependent Injectionmentioning

confidence: 97%

“…Now, if the electron injection into DSA were related to the same mechanism responsible for their heating, a direct consequence would be an electron injection efficiency inversely proportional to the shock speed. This scenario has been investigated by Arbutina & Zeković (2021) by means of PIC simulations. They found that both electrons and protons develop a non-thermal tail which starts at a momentum 𝑝 inj,i = 𝜉 i 𝑝 th,i where 𝑝 th,i is the thermal momentum of each species 𝑖.…”

Section: Results For Time Dependent Injectionmentioning

confidence: 99%

“…Their main finding is that 𝜉 i is roughly the same for both species, and that the slope of the electron spectrum above 𝑝 inj,e remains the same at all momenta, in spite of the fact that for 𝑝 inj,e < 𝑝 < 𝑝 inj,p electrons are pre-accelerated by a mechanism different than DSA. As a consequence, Arbutina & Zeković (2021) got the following approximate expression for the electron to proton ratio:…”

Section: Results For Time Dependent Injectionmentioning

confidence: 99%

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Cosmic-ray electrons released by supernova remnants

Morlino,

Celli

2021

Preprint

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The process that allows cosmic rays (CRs) to escape from their sources and be released into the Galaxy is still largely unknown. The comparison between CR electron and proton spectra measured at Earth suggests that electrons are released with a spectrum steeper than protons by Δ𝑠 ep ∼ 0.3 for energies above ∼ 10 GeV and by Δ𝑠 ep ∼ 1.2 above ∼ 1 TeV. Assuming that both species are accelerated at supernova remnant (SNR) shocks, we here explore two possible scenarios that can in principle justify steeper electron spectra: i) energy losses due to synchrotron radiation in an amplified magnetic field, and ii) time dependent acceleration efficiency. We account for magnetic field amplification (MFA) produced by either CR-induced instabilities or by magneto-hydrodynamics (MHD) instabilities using a parametric description. We show that both mechanisms are required to explain the electron spectrum. In particular synchrotron losses can produce a significant electron steepening only above ∼ 1 TeV, while a time dependent acceleration can explain the spectrum at lower energies if the electron injection into diffusive shock acceleration (DSA) is inversely proportional to the shock speed. We discuss observational and theoretical evidences supporting such a behavior. In addition, we predict two additional spectral features: a spectral break below ∼ few GeV (as required by existing observations) due to the acceleration efficiency drop during the adiabatic phase and a spectral hardening above ∼ 20 TeV (where no data are available yet) resulting from electrons escaping from the shock precursor.

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“…In particular, it has been shown that in the nonrelativistic flows the Weibel instability can amplify the magnetic field energy, up to ∼ 1% of the bulk kinetic energy (e.g., Kato & Takabe 2008;Huntington et al 2015). In addition, recent PIC simulations indicate the evidence of full DSA at Weibel-mediated shocks (Fiuza et al 2020;Arbutina & Zeković 2021). These previous studies focused on high-M A shocks in relatively low β 1 plasmas.…”

Section: Introductionmentioning

confidence: 99%

Cosmic Ray Acceleration and Nonthermal Radiation at Accretion Shocks in the Outer Regions of Galaxy Clusters

Ha¹,

Ryu²,

Kang³

2022

Preprint

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Cosmology models predict that external accretion shocks form in the outer region of galaxy clusters due to supersonic gas infall from filaments and voids in the cosmic web. They are characterized by high sonic and Alfvénic Mach numbers, M s ∼ 10 − 10 2 and M A ∼ 10 2 − 10 3 , and propagate into weakly magnetized plasmas of β ≡ P g /P B 10 2 . Although strong accretion shocks are expected to be efficient accelerators of cosmic rays (CRs), nonthermal signatures of shock-accelerated CRs around clusters have not been confirmed, and detailed acceleration physics at such shocks has yet to be understood. In this study, we first establish through two-dimensional particle-in-cell simulations that at strong high-β shocks electrons can be pre-energized via stochastic Fermi acceleration owing to the ion-Weibel instability in the shock transition region, possibly followed by injection into diffusive shock acceleration. Hence, we propose that the models derived from conventional thermal leakage injection may be employed for the acceleration of electrons and ions at accretion shocks as well. Applying these analytic models to numerical shock zones identified in structure formation simulations, we estimate nonthermal radiation, such as synchrotron and inverse-Compton (IC) emission due to CR electrons, and π 0 -decay γ-rays due to CR protons, around simulated clusters. Our models with the injection parameter, Q ≈ 3.5 − 3.8, predict synthetic synchrotron maps, which seem consistent with recent radio observations of the Coma cluster. However, the detection of nonthermal IC X-rays and γ-rays from accretion shocks would be quite challenging. We suggest that the proposed analytic models may be adopted as generic recipes for CR production at cosmological shocks.

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Non-linear diffusive shock acceleration: A recipe for injection of electrons

Cited by 18 publications

References 81 publications

Proton acceleration in thermonuclear nova explosions revealed by gamma rays

Proton acceleration in thermonuclear nova explosions revealed by gamma rays

Cosmic-ray electrons released by supernova remnants

Cosmic Ray Acceleration and Nonthermal Radiation at Accretion Shocks in the Outer Regions of Galaxy Clusters

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