THE MAXIMUM ENERGY OF ACCELERATED PARTICLES IN RELATIVISTIC COLLISIONLESS SHOCKS

By L. Sironi, A. Spitkovsky, J. Arons. 2013

235 citations recorded by the source corpus.

The afterglow emission from gamma-ray bursts (GRBs) is usually interpreted as synchrotron radiation from electrons accelerated at the GRB external shock that propagates with relativistic velocities into the magnetized interstellar medium. By means of multi-dimensional particle-in-cell simulations, we investigate the acceleration performance of weakly magnetized relativistic shocks, in the magnetization range 0 ≲ σ ≲ 10−1. The pre-shock magnetic field is orthogonal to the flow, as generically expected for relativistic shocks. We find that relativistic perpendicular shocks propagating in electron–positron plasmas are efficient particle accelerators if the magnetization is σ ≲ 10−3. For electron–ion plasmas, the transition to efficient acceleration occurs for σ ≲ 3 × 10−5. Here, the acceleration process proceeds similarly for the two species, since the electrons enter the shock nearly in equipartition with the ions, as a result of strong pre-heating in the self-generated upstream turbulence. In both electron–positron and electron–ion shocks, we find that the maximum energy of the accelerated particles scales in time as εmax∝t1/2. This scaling is shallower than the so-called (and commonly assumed) Bohm limit εmax∝t, and it naturally results from the small-scale nature of the Weibel turbulence generated in the shock layer. In magnetized plasmas, the energy of the accelerated particles increases until it reaches a saturation value εsat/γ0mic2 ∼ σ−1/4, where γ0mic2 is the mean energy per particle in the upstream bulk flow. Further energization is prevented by the fact that the self-generated turbulence is confined within a finite region of thickness ∝σ−1/2 around the shock. Our results can provide physically grounded inputs for models of non-thermal emission from a variety of astrophysical sources, with particular relevance to GRB afterglows.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/3b8e47f2f0b9e76d431c336ac0a2e6717d6dfca2

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. B. Metzger
2. E. Berger
3. L. Sironi
4. D. Giannios
5. Bing Zhang
6. M. Petropoulou
7. W. Fong
8. Raffaella Margutti

In Nuclear and High Energy Physics

1. L. Sironi
2. M. Petropoulou
3. D. Giannios
4. A. Spitkovsky
5. U. Keshet
6. M. Lemoine
7. B. Metzger
8. E. Berger

Citations in the corpus

• Smilei : A collaborative, open-source, multi-purpose particle-in-cell code for plasma simulation (2017, methodology): “The long-standing problem of describing collisionless shock formation has gained renewed interest as PIC simulations provide insight into the micro-physics of these non-linear structures [68, 69, 70].”
• The Binary Neutron Star Event LIGO/Virgo GW170817 160 Days after Merger: Synchrotron Emission across the Electromagnetic Spectrum (2018, background): “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).”
• Relativistic Shocks: Particle Acceleration and Magnetization (2015, methodology): “In contrast, superluminal shocks (θ & θcrit) show negligible particle acceleration (Gallant et al. 1992; Hoshino 2008; Sironi and Spitkovsky 2009a, 2011b; Sironi et al. 2013).”
• Plasmoids in relativistic reconnection, from birth to adulthood: first they grow, then they go (2016, methodology): “…inflow, we employ two moving injectors (receding fromy = 0 at the speed of light along±ŷ) and an expanding simulation box, a technique that we have extensively employed in our studies of relativistic shocks (Sironi & Spitkovsky 2009, 2011b; Sironi et al. 2013) and relativistic reconnection (SS14).”
• Relativistic Jets Shine through Shocks or Magnetic Reconnection (2015, methodology): “…of shock compression(as opposed to fields generated via plasma instabilities at the shock front) and that the upstream region is sufficiently magnetized for the superluminal constraint to hold, i.e.,σ & 10−3 in electron-positron shocks andσ & 10−4 in electron-proton shocks (Sironi et al. 2013).”
• RELATIVISTIC RECONNECTION: AN EFFICIENT SOURCE OF NON-THERMAL PARTICLES (2014, background): “2, harder than in relativistic shocks (Sironi & Spitkovsky 2011b; Sironi et al. 2013).”