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Abstract We present a statistical analysis of >2,100 bipolar electrostatic solitary waves (ESWs) collected from 10 quasi‐perpendicular Earth's bow shock crossings by Magnetospheric Multiscale spacecraft. We developed and implemented a correction procedure for reconstruction of actual electric fields, velocities, and other properties of ESW, whose spatial scales are typically comparable with or smaller than spatial distance between voltage‐sensitive probes. We found that more than 95% of the ESW are of negative polarity with amplitudes typically below a few Volts and 0.1Te(5–30 V or 0.1–0.3Tefor a few percent of ESW), spatial scales of 10–100 m orλD–10λD, and velocities from a few tens to a few hundred km/s that is on the order of local ion‐acoustic speed. The spatial scales of ESW are correlated with local Debye lengthλD. The ESW have electric fields generally oblique to magnetic field and they propagate highly oblique to shock normalN; more than 80% of ESW propagate within 30° of the shock planeLM. In the shock plane, ESW typically propagates within a few tens of degrees of local magnetic field projectionBLMand preferentially opposite toN × BLM. We argue that the ESW of negative polarity are ion holes produced by ion‐ion streaming instabilities. We estimate ion hole lifetimes to be 10–100 ms, or 1–10 km in terms of traveling distance. The revealed statistical properties will be useful for quantitative studies of electron thermalization in the Earth's bow shock.
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Long-term Evolution of Relativistic Unmagnetized Collisionless Shocks
Abstract We study a relativistic collisionless electron–positron shock propagating into an unmagnetized ambient medium using 2D particle-in-cell simulations of unprecedented duration and size. The shock generates intermittent magnetic structures of increasingly larger size as the simulation progresses. Toward the end of our simulation, at around 26,000 plasma times, the magnetic coherence scale approachesλ∼ 100 plasma skin depths, both ahead and behind the shock front. We anticipate a continued growth ofλbeyond the time span of our simulation, as long as the shock accelerates particles to increasingly higher energies. The post-shock field is concentrated in localized patches, which maintain a local magnetic energy fractionεB∼ 0.1. Particles randomly sampling the downstream fields spend most of their time in low field regions (εB≪ 0.1) but emit a large fraction of the synchrotron power in the localized patches with strong fields (εB∼ 0.1). Our results have important implications for models of gamma-ray burst afterglows.
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- PAR ID:
- 10494965
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 963
- Issue:
- 2
- ISSN:
- 2041-8205
- Format(s):
- Medium: X Size: Article No. L44
- Size(s):
- Article No. L44
- Sponsoring Org:
- National Science Foundation
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