Ion Acceleration at the Quasi-Parallel Bow Shock: Decoding the Signature of Injection

Sundberg, T.; Haynes, Christopher T.; Burgess, David; Mazelle, C.

doi:10.3847/0004-637x/820/1/21

Cited by 31 publications

(46 citation statements)

References 49 publications

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“…Those suprathermal electrons are expected to be injected to the full Fermi I acceleration and eventually accelerated to highly relativistic energies. Such a hybrid process combining specular reflection with SDA and DSA between the shock ramp and upstream waves is found to be effective at both quasi-perpendicular and quasi-parallel collisionless shocks (Park et al 2015;Sundberg et al 2016). However, the injection momentum for electrons is not well constrained, since the development of the full DSA power-law spectrum extending to  p m c 1 e has not been established in the simulations due to severe computational requirements for these PIC plasma simulations.…”

Section: Dsa Solutions At the Shockmentioning

confidence: 99%

Shock Acceleration Model for the Toothbrush Radio Relic

Kang¹,

Ryu²,

Jones³

2017

ApJ

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Although many of the observed properties of giant radio relics detected in the outskirts of galaxy clusters can be explained by relativistic electrons accelerated at merger-driven shocks, significant puzzles remain. In the case of the so-called Toothbrush relic, the shock Mach number estimated from X-ray observations (is substantially weaker than that inferred from the radio spectral index (. Toward understanding such a discrepancy, we here consider the following diffusive shock acceleration (DSA) models: (1) weak-shock models with  M 2 s and a preexisting population of cosmic-ray electrons (CRe) with a flat energy spectrum, and (2) strong-shock models with » M 3 s and either shock-generated suprathermal electrons or preexisting fossil CRe. We calculate the synchrotron emission from the accelerated CRe, following the time evolution of the electron DSA, and the subsequent radiative cooling and postshock turbulent acceleration (TA). We find that both models could reproduce reasonably well the observed integrated radio spectrum of the Toothbrush relic, but the observed broad transverse profile requires the stochastic acceleration by downstream turbulence, which we label "turbulent acceleration" or TA to distinguish it from DSA. Moreover, to account for the almost uniform radio spectral index profile along the length of the relic, the weak-shock models require a preshock region over 400kpc with a uniform population of preexisting CRe with a high cutoff energy (40 GeV). Due to the short cooling time, it is challenging to explain the origin of such energetic electrons. Therefore, we suggest the strong-shock models with low-energy seed CRe (150 MeV) are preferred for the radio observations of this relic.

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Section: Dsa Solutions At the Shockmentioning

confidence: 99%

Shock Acceleration Model for the Toothbrush Radio Relic

Kang¹,

Ryu²,

Jones³

2017

ApJ

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“…We performed 2D hybrid simulations to investigate the influence of He ++ on shock dynamics and particle thermalization for different θ Bn initial values and different number content of He ++ particles. The two dimensional simulations were performed using the hybrid Particle‐In‐Cell (PIC) code HYPSI (Burgess et al, ; Sundberg et al, ), which is based on the CAM‐CL (see Matthews, for details) algorithm. Under this approach, protons and He ++ particles are treated kinetically and advanced using the standard PIC method.…”

Section: Simulation Setupmentioning

confidence: 99%

“…In quasi‐parallel shocks, the reflected ions can escape back to the upstream side along the magnetic field lines where their interaction with the solar wind (SW) particles can lead to excitation of upstream waves including ultra‐low‐frequency (ULF) waves, which can evolve into shocklets, and other large‐amplitude magnetic structures (Blanco‐Cano, ; Russell & Hoppe, ; Wilson, ). Consequently, the region upstream of a quasi‐parallel shock is intimately linked to the generation of high‐energy upstream ions and is in particular related to the extraction of thermal particles from the upstream side of the shock into the population of energetic ions (Burgess, ; Scholer & Burgess, , ; Su et al, , ; Sundberg et al, ).…”

Section: Introductionmentioning

confidence: 99%

Influence of He⁺⁺and Shock Geometry on Interplanetary Shocks in the Solar Wind: 2D Hybrid Simulations

et al. 2020

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After protons, alpha particles (He ++ ) are the most important ion species in the solar wind, constituting typically about 5% of the total ion number density. Due to their different charge-to-mass ratio, protons and He ++ particles are accelerated differently when they cross the electrostatic potential in a collisionless shock. This behavior can produce changes in the velocity distribution function (VDF) for both species generating anisotropy in the temperature, which is considered to be the energy source for various phenomena such as ion cyclotron and mirror mode waves. How these changes in temperature anisotropy and shock structure depend on the percentage of He ++ particles and the geometry of the shock is not completely understood. In this paper, we have performed various 2D local hybrid simulations (particle ions, massless fluid electrons) with similar characteristics (e.g., Mach number) to interplanetary shocks for both quasi-parallel and quasi-perpendicular geometries self-consistently including different percentages of He ++ particles. We have found changes in the shock transition behavior as well as in the temperature anisotropy as functions of both the shock geometry and He ++ particle abundance: The change of the initial Bn leads to variations of the efficiency with which particles can escape to the upstream region facilitating or not the formation of compressive structures in the magnetic field that will produce increments in perpendicular temperature. The regions where both temperature anisotropy and compressive fluctuations appear tend to be more extended and reach higher values as the He ++ content in the simulations increases.

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“…Maxwell's equations are solved in the low‐frequency Darwin limit using the CAM‐CL algorithm described by Matthews (). Here we use the hybrid code HYPSI, as utilized by previous shock studies (Burgess et al, ; Sundberg et al, ).…”

Section: Simulationsmentioning

confidence: 99%

MMS Observations and Hybrid Simulations of Surface Ripples at a Marginally Quasi‐Parallel Shock

et al. 2017

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Simulations and observations of collisionless shocks have shown that deviations of the nominal local shock normal orientation, that is, surface waves or ripples, are expected to propagate in the ramp and overshoot of quasi‐perpendicular shocks. Here we identify signatures of a surface ripple propagating during a crossing of Earth's marginally quasi‐parallel (θBn∼45∘) or quasi‐parallel bow shock on 27 November 2015 06:01:44 UTC by the Magnetospheric Multiscale (MMS) mission and determine the ripple's properties using multispacecraft methods. Using two‐dimensional hybrid simulations, we confirm that surface ripples are a feature of marginally quasi‐parallel and quasi‐parallel shocks under the observed solar wind conditions. In addition, since these marginally quasi‐parallel and quasi‐parallel shocks are expected to undergo a cyclic reformation of the shock front, we discuss the impact of multiple sources of nonstationarity on shock structure. Importantly, ripples are shown to be transient phenomena, developing faster than an ion gyroperiod and only during the period of the reformation cycle when a newly developed shock ramp is unaffected by turbulence in the foot. We conclude that the change in properties of the ripple observed by MMS is consistent with the reformation of the shock front over a time scale of an ion gyroperiod.

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Ion Acceleration at the Quasi-Parallel Bow Shock: Decoding the Signature of Injection

Cited by 31 publications

References 49 publications

Shock Acceleration Model for the Toothbrush Radio Relic

Shock Acceleration Model for the Toothbrush Radio Relic

Influence of He⁺⁺and Shock Geometry on Interplanetary Shocks in the Solar Wind: 2D Hybrid Simulations

MMS Observations and Hybrid Simulations of Surface Ripples at a Marginally Quasi‐Parallel Shock

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Ion Acceleration at the Quasi-Parallel Bow Shock: Decoding the Signature of Injection

Cited by 31 publications

References 49 publications

Shock Acceleration Model for the Toothbrush Radio Relic

Shock Acceleration Model for the Toothbrush Radio Relic

Influence of He++and Shock Geometry on Interplanetary Shocks in the Solar Wind: 2D Hybrid Simulations

MMS Observations and Hybrid Simulations of Surface Ripples at a Marginally Quasi‐Parallel Shock

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Influence of He⁺⁺and Shock Geometry on Interplanetary Shocks in the Solar Wind: 2D Hybrid Simulations