Observational Evidence of Magnetic Reconnection in the Terrestrial Foreshock Region

Abstract Electron heating/acceleration in the foreshock, by which electrons may be energized beyond thermal energies prior to encountering the bow shock, is very important for the bow shock dynamics. And then these electrons would be more easily injected into a process like diffusive shock acceleration. Many mechanisms have been proposed to explain electrons heating/acceleration in the foreshock. Magnetic reconnection is one possible candidate. Taking advantage of the Magnetospheric Multiscale mission, we present two magnetic reconnection events in the dawnside and duskside ion foreshock region, respectively. Super-Alfvénic electron outflow, demagnetization of the electrons and the ions, and crescent electron distributions in the plane perpendicular to the magnetic field are observed in the sub-ion-scale current sheets. Moreover, strong energy conversion from the fields to the plasmas and significant electron temperature enhancement are observed. Our observations provide direct evidence that magnetic reconnection could occur in the foreshock region and heat/accelerate the electrons therein.

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On the alignment of velocity and magnetic fields within magnetosheath jets

Annales Geophysicae ◽

10.5194/angeo-38-287-2020 ◽

2020 ◽

Vol 38 (2) ◽

pp. 287-296

Author(s):

Ferdinand Plaschke ◽

Maria Jernej ◽

Heli Hietala ◽

Laura Vuorinen

Keyword(s):

Magnetic Fields ◽

Entire Range ◽

Dynamic Pressure ◽

Bow Shock ◽

Superposed Epoch Analysis ◽

Magnetospheric Multiscale ◽

Study Results ◽

Epoch Analysis ◽

The Magnetic Field

Abstract. Jets in the subsolar magnetosheath are localized enhancements in dynamic pressure that are able to propagate all the way from the bow shock to the magnetopause. Due to their excess velocity with respect to their environment, they push slower ambient plasma out of their way, creating a vortical plasma motion in and around them. Simulations and case study results suggest that jets also modify the magnetic field in the magnetosheath on their passage, aligning it more with their velocity. Based on Magnetospheric Multiscale (MMS) jet observations and corresponding superposed epoch analyses of the angles ϕ between the velocity and magnetic fields, we can confirm that this suggestion is correct. However, while the alignment is more significant for faster than for slower jets, and for jets observed close to the bow shock, the overall effect is small: typically, reductions in ϕ of around 10∘ are observed at jet core regions, where the jets' velocities are largest. Furthermore, time series of ϕ pertaining to individual jets significantly deviate from the superposed epoch analysis results. They usually exhibit large variations over the entire range of ϕ: 0 to 90∘. This variability is commonly somewhat larger within jets than outside them, masking the systematic decrease in ϕ at core regions of individual jets.

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Electron energization in quasi-parallel shocks

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038915 ◽

2020 ◽

Vol 642 ◽

pp. A47

Author(s):

Adrian Hanusch ◽

Tatyana V. Liseykina ◽

Mikhail A. Malkov

Keyword(s):

Supernova Remnants ◽

Cosmic Ray ◽

Bow Shock ◽

Shock Acceleration ◽

Diffusive Shock Acceleration ◽

Proton Temperature ◽

Earth’S Bow Shock ◽

Long Time ◽

Spatial Dimensionality

Context. In situ observations of energetic particles at the Earth’s bow-shock that are attainable by the satellite missions have fostered the opinion for a long time that electrons are most efficiently accelerated in a quasi-perpendicular shock geometry. However, shocks that are deemed to be responsible for the production of cosmic ray electrons and their radiation from sources such as supernova remnants are much more powerful and larger than the Earth’s bow-shock. Their remote observations and also in situ measurements at Saturn’s bow shock, that is, the strongest shock in the Solar System, suggest that electrons are accelerated very efficiently in the quasi-parallel shocks as well. Aims. In this paper we investigate the possibility that protons that are accelerated to high energies create sufficient wave turbulence, which is necessary for the electron preheating and subsequent injection into the diffusive shock acceleration in a quasi-parallel shock geometry. Methods. An additional test-particle-electron population, which is meant to be a low-density addition to the electron core-distribution on which the hybrid simulation operates, is introduced. Our purpose is to investigate how these electrons are energized by the “hybrid” electromagnetic field. The reduced spatial dimensionality allowed us to dramatically increase the number of macro-ions per numerical cell and achieve the converged results for the velocity distributions of test electrons. Results. We discuss the electron preheating mechanisms, which can make a significant part of thermal electrons accessible to the ion-driven waves observed in hybrid simulations. We find that the precursor wave field supplied by ions has a considerable potential to preheat the electrons before they are shocked at the subshock. Our results indicate that a downstream thermal equilibration of the hot test electrons and protons does not occur. Instead, the resulting electron-to-proton temperature ratio is a decreasing function of the shock Mach number, MA, which has a tendency for a saturation at high MA.

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Diffusive shock acceleration - Comparison of a unified shock model to bow shock observations

The Astrophysical Journal ◽

10.1086/165384 ◽

1987 ◽

Vol 318 ◽

pp. 474 ◽

Cited By ~ 33

Author(s):

Donald C. Ellison ◽

Eberhard Moebius

Keyword(s):

Bow Shock ◽

Shock Acceleration ◽

Shock Model ◽

Diffusive Shock Acceleration

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On the influence of supra-thermal particle acceleration on the morphology of low-Mach, high-β shocks

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1771 ◽

2020 ◽

Vol 496 (3) ◽

pp. 3198-3208

Author(s):

Allard Jan van Marle

Keyword(s):

Mach Number ◽

Galaxy Cluster ◽

Cosmic Ray ◽

Shock Acceleration ◽

Diffusive Shock Acceleration ◽

Particle Injection ◽

Particle In Cell ◽

Injection Process ◽

The Magnetic Field ◽

High Computational Efficiency

ABSTRACT When two galaxy clusters encounter each other, the interaction results in a collisionless shock that is characterized by a low (1–4) sonic Mach number, and a high-Alfvénic Mach number. Our goal is to determine if, and to what extent, such shocks can accelerate particles to sufficient velocities that they can contribute to the cosmic ray spectrum. We combine two different computational methods, magnetohydrodynamics (MHD) and particle-in-cell (PIC) into a single code that allows us to take advantage of the high computational efficiency of MHD while maintaining the ability to model the behaviour of individual non-thermal particles. Using this method, we perform a series of simulations covering the expected parameter space of galaxy cluster collision shocks. Our results show that for shocks with a sonic Mach number below 2.25 no diffusive shock acceleration can take place because of a lack of instabilities in the magnetic field, whereas for shocks with a sonic Mach number $\ge \, 3$ the acceleration is efficient and can accelerate particles to relativistic speeds. In the regime between these two extremes, diffusive shock acceleration can occur but is relatively inefficient because of the time- and space-dependent nature of the instabilities. For those shocks that show efficient acceleration, the instabilities in the upstream gas increase to the point where they change the nature of the shock, which, in turn, will influence the particle injection process.

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Effects of nonlinear Alfvén wave interaction on particle diffusive shock acceleration. The Earth’s bow shock

Astronomy Letters ◽

10.1134/1.1505508 ◽

2002 ◽

Vol 28 (9) ◽

pp. 632-640 ◽

Cited By ~ 5

Author(s):

E. G. Berezhko ◽

S. I. Petukhov ◽

S. N. Taneev

Keyword(s):

Wave Interaction ◽

Bow Shock ◽

Alfven Wave ◽

Shock Acceleration ◽

Diffusive Shock Acceleration ◽

Earth’S Bow Shock

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Cosmic rays and stochastic magnetic reconnection in the heliotail

Nonlinear Processes in Geophysics ◽

10.5194/npg-19-351-2012 ◽

2012 ◽

Vol 19 (3) ◽

pp. 351-364 ◽

Cited By ~ 8

Author(s):

P. Desiati ◽

A. Lazarian

Keyword(s):

Magnetic Field ◽

Cosmic Rays ◽

Magnetic Reconnection ◽

Supernova Remnants ◽

Average Energy ◽

Cosmic Ray ◽

Galactic Cosmic Rays ◽

Shock Acceleration ◽

Diffusive Shock Acceleration ◽

The Galaxy

Abstract. Galactic cosmic rays are believed to be generated by diffusive shock acceleration processes in Supernova Remnants, and the arrival direction is likely determined by the distribution of their sources throughout the Galaxy, in particular by the nearest and youngest ones. Transport to Earth through the interstellar medium is expected to affect the cosmic ray properties as well. However, the observed anisotropy of TeV cosmic rays and its energy dependence cannot be explained with diffusion models of particle propagation in the Galaxy. Within a distance of a few parsec, diffusion regime is not valid and particles with energy below about 100 TeV must be influenced by the heliosphere and its elongated tail. The observation of a highly significant localized excess region of cosmic rays from the apparent direction of the downstream interstellar flow at 1–10 TeV energies might provide the first experimental evidence that the heliotail can affect the transport of energetic particles. In particular, TeV cosmic rays propagating through the heliotail interact with the 100–300 AU wide magnetic field polarity domains generated by the 11 yr cycles. Since the strength of non-linear convective processes is expected to be larger than viscous damping, the plasma in the heliotail is turbulent. Where magnetic field domains converge on each other due to solar wind gradient, stochastic magnetic reconnection likely occurs. Such processes may be efficient enough to re-accelerate a fraction of TeV particles as long as scattering processes are not strong. Therefore, the fractional excess of TeV cosmic rays from the narrow region toward the heliotail direction traces sightlines with the lowest smearing scattering effects, that can also explain the observation of a harder than average energy spectrum.

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Magnetic Curvature Analysis on Reconnection Related Structures at Earth’s Magnetopause

10.5194/egusphere-egu2020-3764 ◽

2020 ◽

Author(s):

Yi Qi ◽

Christopher T. Russell ◽

Robert J. Strangeway ◽

Yingdong Jia ◽

Roy B. Torbert ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Magnetic Reconnection ◽

Solar Wind Plasma ◽

Radius Of Curvature ◽

Plasma Properties ◽

Magnetospheric Multiscale ◽

Reconnection Site ◽

Field Lines ◽

The Magnetic Field

<p>Magnetic reconnection is a mechanism that allows rapid and explosive energy transfer from the magnetic field to the plasma. The magnetopause is the interface between the shocked solar wind plasma and Earth&#8217;s magnetosphere. Reconnection enables the transport of momentum from the solar wind into Earth&#8217;s magnetosphere. Because of its importance in this regard, magnetic reconnection has been extensively studied in the past and is the primary goal of the ongoing Magnetospheric Multiscale (MMS) mission. During magnetic reconnection, the originally anti-parallel fields annihilate and reconnect in a thinned current sheet. In the vicinity of a reconnection site, a prominently increased curvature of the magnetic field (and smaller radius of curvature) marks the region where the particles start to deviate from their regular gyro-motion and become available for energy conversion. Before MMS, there were no closely separated multi-spacecraft missions capable of resolving these micro-scale curvature features, nor examining particle dynamics with sufficiently fast cadence.</p><p>In this study, we use measurements from the four MMS spacecraft to determine the curvature of the field lines and the plasma properties near the reconnection site. We use this method to study FTEs (flux ropes) on the magnetopause, and the interaction between co-existing FTEs. Our study not only improves our understanding of magnetic reconnection, but also resolves the relationship between FTEs and structures on the magnetopause.</p>

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Oblique Shocks in Extragalactic Jets

Symposium - International Astronomical Union ◽

10.1017/s0074180900190746 ◽

1990 ◽

Vol 140 ◽

pp. 437-437

Author(s):

D. Fraix-Burnet

Keyword(s):

Magnetic Field ◽

High Resolution ◽

Shock Front ◽

Shock Acceleration ◽

Relativistic Electrons ◽

Optical Polarization ◽

Diffusive Shock Acceleration ◽

Extragalactic Jets ◽

The Magnetic Field ◽

Oblique Shocks

In the framework of the diffusive shock acceleration of relativistic electrons in extragalactic jets, we show that it is possible to derive the speed of the jet. For this purpose, we transform continuity relations through an oblique shock front into the reference frame of the observer. We apply these calculations to knot A of the M87 jet. Measuring the deviation of the fluid through the shock front from high-resolution radio maps and the deviation of the magnetic field from optical polarization maps (Fraix-Burnet et al., 1989), we derive speeds of about 0.01 c (Fraix-Burnet and Biermann, in preparation). The compression ratio is most probably 4 and the magnetic field is nearly parallel to the shock front both upstream and downstream.

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Interaction of Jets with Clouds in Extragalactic Radio Sources

Symposium - International Astronomical Union ◽

10.1017/s0074180900175473 ◽

1994 ◽

Vol 159 ◽

pp. 346-346

Author(s):

V. Fedorenko ◽

A. Zentsova ◽

T. J.-L. Courvoisier ◽

S. Paltani

Keyword(s):

Magnetic Field ◽

Supernova Remnants ◽

Shock Acceleration ◽

Stellar Winds ◽

Radio Sources ◽

Red Giants ◽

Diffusive Shock Acceleration ◽

Extragalactic Jets ◽

The Magnetic Field ◽

Very High

Several points indicate that extragalactic jets can interact with dense gaseous obstacles which occur on their ways. Examples of these interactions are the knotty structure of the radio and optical jet in M 87 and in other objects. These observations have been interpreted by Blandford & Königl in terms of collision of a jet with supernova remnants. We have reanalysed this idea taking into account new observations and improvements in the theory of diffusive shock acceleration. We find that the model requires a very high supernova birthrate (∼ 1 SN/year), which is not observed. It is more probable that the “obstacles” are formed by the stellar winds from the red giants. We estimate that the value of the magnetic field is ∼ 10−5 G in the interaction region (r=1kpc) (paper in preparation).

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