On the Structure of Relativistic Collisionless Shocks in Electron-Ion Plasmas

By A. Spitkovsky. 2007

298 citations recorded by the source corpus.

Relativistic collisionless shocks in electron-ion plasmas are thought to occur in the afterglow phase of gamma-ray bursts (GRBs) and in other environments where relativistic flows interact with the interstellar medium. A particular regime of shocks in an unmagnetized plasma has generated much interest for GRB applications. In this Letter, we present ab initio particle-in-cell simulations of unmagnetized relativistic electron-ion shocks. Using long-term 2.5-dimensional simulations with ion-electron mass ratios from 16 to 1000, we resolve the shock formation and reach a steady state shock structure beyond the initial transient. We find that even at high ion-electron mass ratios initially unmagnetized shocks can be effectively mediated by the ion Weibel instability with a typical shock thickness of ~20 ion skin depths. Upstream of the shock, the interaction with merging ion current filaments heats the electron component, so that the postshock flow achieves near-equipartition between the ions and electrons, with the electron temperature reaching 50% of the ion temperature. This energy exchange helps to explain the large electron energy fraction inferred from GRB afterglow observations.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/648cc9b7c79f657559f9123c00bf54a1d6944d3f

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In Astronomy and Astrophysics

1. Bing Zhang
2. B. Metzger
3. E. Berger
4. L. Sironi
5. D. Giannios
6. A. Spitkovsky
7. J. Arons
8. M. Petropoulou

In Atomic and Molecular Physics, and Optics

1. L. Sironi
2. D. Giannios
3. M. Petropoulou
4. U. Keshet
5. M. Lemoine
6. A. Bret
7. A. Spitkovsky
8. J. Arons

Citations in the corpus

• Relativistic Shocks: Particle Acceleration and Magnetization (2015, methodology): “The stream of shock-accelerated particles propagates ahead of the shock, triggering the Weibel instability.”
• FERMI OBSERVATIONS OF GRB 090510: A SHORT–HARD GAMMA-RAY BURST WITH AN ADDITIONAL, HARD POWER-LAW COMPONENT FROM 10 keV TO GeV ENERGIES (2010, background): “Recent particle in cell simulations of relativistic collisionless shocks (Spitkovsky 2008a,b; Martins et al. 2009) suggest that ξe is fairly small (of the order of a few percent), which may in our case allow hνm of several MeV even for low values of ǫB .”
• Nonrelativistic Collisionless Shocks in Unmagnetized Electron-Ion Plasmas (2008, background): “This structure would be formed through the Weibel-type instability like the relativistic shocks in unmagnetized plasmas (Kato 2007; Spitkovsky 2008).”
• PARTICLE ACCELERATION IN RELATIVISTIC MAGNETIZED COLLISIONLESS ELECTRON–ION SHOCKS (2010, background): “…the incoming plasma can filament, and the shock is mediated by the ion Weibel instability (Weibel 1959; Medvedev & Loeb 1999; Gruzinov & Waxman 1999), which ensures strong electron heating and efficient particle acceleration, for both ions and electrons (Spitkovsky 2008a; Martins et al. 2009).”
• Observation of magnetic field generation via the Weibel instability in interpenetrating plasma flows (2013, background): “At time scales longer than those addressed here, this can also lead to the formation of shock waves and to particle acceleration from these shocks [9, 11].”
• Particle Acceleration in Relativistic Collisionless Shocks: Fermi Process at Last? (2008, background): “…Nishikawa et al. 2003, 2005; Silva et al. 2003; Frederiksen et al. 2004; Hededal et al. 2004), and have been evolved through the shock formation stage in both 2D (Gruzinov 2001; Kato 2007; Spitkovsky 2008, hereafter S08; Chang et al. 2008, herefter CSA08) and 3D (Spitkovsky 2005, hereafter S05).”
• The origin of galactic cosmic rays (2013, unknown): “…(PIC) simulations have been instrumental in reaching a better understanding of the formation of collisionless shocks (both relativistic and non-relativistic) and the initial stages of the acceleration process (Spitkovsky 2008a, 2008b; Sironi and Spitkovsky 2011, Gargaté and Spitkovsky 2012).”
• The Binary Neutron Star Event LIGO/Virgo GW170817 160 Days after Merger: Synchrotron Emission across the Electromagnetic Spectrum (2018, result): “These findings are consistent with the picture favored by magnetic field self-generated by the shock is not uniform in the post-shock region, but decays away from the shock (e.g., Spitkovsky 2008; Chang et al. 2008; Keshet et al. 2009; Martins et al. 2009; Haugbølle 2011; Sironi et al. 2013).”
• PARTICLE ACCELERATION IN RELATIVISTIC MAGNETIZED COLLISIONLESS PAIR SHOCKS: DEPENDENCE OF SHOCK ACCELERATION ON MAGNETIC OBLIQUITY (2009, background): “PIC simulations of relativistic unmagnetized shocks have been presented by Spitkovsky (2005, 2008a), Chang et al. (2008) and Keshet et al. (2008); Spitkovsky (2008b) has shown that unmagnetized shocks naturally produce accelerated particles as part of the shock evolution.”
• Reconciling observed gamma-ray burst prompt spectra with synchrotron radiation? (2010, unknown): “More complex distributions showing several components (e.g. Maxwellian distribution+ non-thermal tail) are observed in some simulations of particle acceleration in ultra-relativistic shocks (Spitkovsky 2008b,a; Martins et al. 2009).”
• Relativistic Jets Shine through Shocks or Magnetic Reconnection (2015, methodology): “First-order Fermi acceleration in relativistic shocks has been demonstrated from first principles (Spitkovsky 2008a,b; Martins et al. 2009; Haugbølle 2011; Sironi et al. 2013).”
• THE MAXIMUM ENERGY OF ACCELERATED PARTICLES IN RELATIVISTIC COLLISIONLESS SHOCKS (2013, background): “Shock Structure The physics of electron-ion unmagnetized shocks has been investigated by Spitkovsky (2008a) and Martins et al. (2009) in 2D and by Haugbølle (2011) in 3D.”
• WEIBEL, TWO-STREAM, FILAMENTATION, OBLIQUE, BELL, BUNEMAN...WHICH ONE GROWS FASTER? (2009, background): “For such settings, filamentation instability has been found leading the linear phase, and the shock formation has so far been analyzed accordingly (Medvedev & Loeb 1999; Spitkovsky 2008a, 2008b).”
• ACCELERATION OF PARTICLES AT THE TERMINATION SHOCK OF A RELATIVISTIC STRIPED WIND (2011, background): “Their energization proceeds in the same way as for a strictly unmagnetized shock, which was discussed by Spitkovsky (2008).”