Whistler critical Mach number and electron acceleration at the bow shock: Geotail observation

Oka, M.; Terasawa, T.; Seki, Yasushi; Fujimoto, M.; Kasaba, Yasumasa; Kojima, Hirotsugu; Shinohara, I.; Matsui, H.; Matsumoto, Hiroshi; Saito, Y.; Mukai, T.

doi:10.1029/2006gl028156

Cited by 73 publications

(94 citation statements)

References 18 publications

(20 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Images of supernova remnant SN1006 show that this emission is inhomogeneous and spatially limited, and so it is of interest to establish whether this emission occurs in the parallel or perpendicular shock regime. At low Mach number shocks at Earth, electron acceleration occurs for perpendicular geometry as seen in the previous section (e.g., Krimigis 1992;Oka et al 2006). More generally however, supernova remnant (SNR) Mach numbers are much higher.…”

Section: The Bow Shock/foreshock As a Site For Particle Accelerationmentioning

confidence: 85%

What Controls the Structure and Dynamics of Earth’s Magnetosphere?

et al. 2014

Self Cite

View full text Add to dashboard Cite

Unlike most cosmic plasma structures, planetary magnetospheres can be extensively studied in situ. In particular, studies of the Earth's magnetosphere over the past few decades have resulted in a relatively good experimental understanding of both its basic structural properties and its response to changes in the impinging solar wind. In this article we provide a broad overview, designed for researchers unfamiliar with magnetospheric physics, of the main processes and parameters that control the structure and dynamics of planetary magnetospheres, especially the Earth's. In particular, we concentrate on the structure and dynamics of three important regions: the bow shock, the magnetopause and the magnetotail. In the final part of this review we describe the current status of global magnetospheric modelling, which is crucial to placing in situ observations in the proper context and providing a better understanding of magnetospheric structure and dynamics under all possible input conditions. Although the parameter regime experienced in the solar system is limited, the plasma physics that is learned by studying planetary magnetospheres can, in principle, be translated to more general studies of cosmic plasma structures. Conversely, studies of cosmic plasma under a wide range of conditions should be used to understand Earth's

show abstract

Section: The Bow Shock/foreshock As a Site For Particle Accelerationmentioning

confidence: 85%

What Controls the Structure and Dynamics of Earth’s Magnetosphere?

et al. 2014

Self Cite

View full text Add to dashboard Cite

show abstract

“…The curved line gives the approximate electron injection threshold based on Oka et al (2006; similar to the threshold presented by Amano & Hoshino 2010). Below this curve the conditions at the shock are predicted to prohibit any efficient injection of electrons into the main acceleration process, whereas above the curve conditions are predicted to lead to efficient electron injection.…”

Section: Discussionmentioning

confidence: 99%

“…Common aspects of many of these proposed mechanisms are interactions between reflected thermal electrons and self-generated whistler waves just upstream of the shock. Oka et al (2006) and Amano & Hoshino (2010) derived similar conditions for the resulting efficient "injection" of electrons, dependent on both the shock angle and Alfvén Mach number.…”

Section: Discussionmentioning

confidence: 99%

“…The latter of these is most relevant for the cosmic ray source problem, despite the fact that maximum particle energies are limited by the far smaller scale of heliospheric shocks compared to their much larger young SNR shock counterparts. Until recently shock-acceleration of electrons had only been identified at quasi-perpendicular shocks (Sarris & Krimigis 1985;Gosling et al 1989;Krimigis 1992;Shimada et al 1999;Oka et al 2006), and the lack of evidence for electron acceleration under quasiparallel conditions has featured heavily in discussions of the "electron injection problem." This is the anticipated inefficiency of resonant interactions between thermal-pool electrons and magnetohydrodynamic (Alfvénic) turbulence, prohibiting any DSA at the shock front (e.g., Shimada et al 1999).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Suprathermal Electrons at Saturn's Bow Shock

Masters

Sulaiman

Sergis

et al. 2016

ApJ

Self Cite

View full text Add to dashboard Cite

The leading explanation for the origin of galactic cosmic rays is particle acceleration at the shocks surrounding young supernova remnants (SNRs), although crucial aspects of the acceleration process are unclear. The similar collisionless plasma shocks frequently encountered by spacecraft in the solar wind are generally far weaker (lower Mach number) than these SNR shocks. However, the Cassini spacecraft has shown that the shock standing in the solar wind sunward of Saturn (Saturnʼs bow shock) can occasionally reach this high-Mach number astrophysical regime. In this regime Cassini has provided the first in situ evidence for electron acceleration under quasi-parallel upstream magnetic conditions. Here we present the full picture of suprathermal electrons at Saturnʼs bow shock revealed by Cassini. The downstream thermal electron distribution is resolved in all data taken by the low-energy electron detector (CAPS-ELS, <28 keV) during shock crossings, but the higher energy channels were at (or close to) background. The high-energy electron detector (MIMI-LEMMS, >18 keV) measured a suprathermal electron signature at 31 of 508 crossings, where typically only the lowest energy channels (<100 keV) were above background. We show that these results are consistent with the theory in which the "injection" of thermal electrons into an acceleration process involves interaction with whistler waves at the shock front, and becomes possible for all upstream magnetic field orientations at high Mach numbers like those of the strong shocks around young SNRs.A future dedicated study will analyze the rare crossings with evidence for relativistic electrons (up to ∼1 MeV).

show abstract

“…• (Oka et al 2006;Gosling et al 1989). Also, radio and X-ray observations of supernova remnants (SNRs) show synchrotron radiation produced by relativistic, nonthermal electrons accelerated in their forward shocks (e.g.…”

Section: Introductionmentioning

confidence: 99%

Electron injection by whistler waves in non-relativistic shocks

Riquelme

Spitkovsky

2012

AIP Conference Proceedings

View full text Add to dashboard Cite

Electron acceleration to non-thermal, ultra-relativistic energies (∼ 10−100 TeV) is revealed by radio and X-ray observations of shocks in young supernova remnants (SNRs). The diffusive shock acceleration (DSA) mechanism is usually invoked to explain this acceleration, but the way in which electrons are initially energized or 'injected' into this acceleration process starting from thermal energies is an unresolved problem. In this paper we study the initial acceleration of electrons in non-relativistic shocks from first principles, using two-and three-dimensional particle-in-cell (PIC) plasma simulations. We systematically explore the space of shock parameters (the Alfvénic Mach number, M A , the shock velocity, v sh , the angle between the upstream magnetic field and the shock normal, θ Bn , and the ion to electron mass ratio, m i /m e ). We find that significant non-thermal acceleration occurs due to the growth of oblique whistler waves in the foot of quasi-perpendicular shocks. This acceleration strongly depends on using fairly large numerical mass ratios, m i /m e , which may explain why it had not been observed in previous PIC simulations of this problem. The obtained electron energy distributions show power law tails with spectral indices up to α ∼ 3 − 4. The maximum energies of the accelerated particles are consistent with the electron Larmor radii being comparable to that of the ions, indicating potential injection into the subsequent DSA process. This injection mechanism, however, requires the shock waves to have fairly low Alfénic Mach numbers, M A 20, which is consistent with the theoretical conditions for the growth of whistler waves in the shock foot (M A (m i /m e ) 1/2 ). Thus, if the whistler mechanism is the only robust electron injection process at work in SNR shocks, then SNRs that display non-thermal emission must have significantly amplified upstream magnetic fields. Such field amplification is likely achieved by the escaping cosmic rays, so electron and proton acceleration in SNR shocks must be interconnected.

show abstract

Whistler critical Mach number and electron acceleration at the bow shock: Geotail observation

Cited by 73 publications

References 18 publications

What Controls the Structure and Dynamics of Earth’s Magnetosphere?

What Controls the Structure and Dynamics of Earth’s Magnetosphere?

Suprathermal Electrons at Saturn's Bow Shock

Electron injection by whistler waves in non-relativistic shocks

Contact Info

Product

Resources

About