Particle Acceleration in Relativistic Plasma Turbulence

Comisso, Luca; Sironi, Lorenzo

doi:10.1103/physrevlett.121.255101

Cited by 179 publications

(225 citation statements)

References 75 publications

Supporting

Mentioning

202

Contrasting

Order By: Relevance

“…An animation showing the current density Jz in different xy slices can be found at https://doi.org/10.7916/d8-prt9-kn88. vidio et al 2009;Wan et al 2013;Franci et al 2017;Haggerty et al 2017;Dong et al 2018;Comisso & Sironi 2018;Papini et al 2019), play an important role for particle injection into the acceleration process (Comisso & Sironi 2018). Finally, we also point out that in the strongly magnetized regime of plasma turbulence investigated here, the plasma bulk speed can reach very high values.…”

Section: Plasma Turbulencesupporting

confidence: 56%

“…To identify this moment, that we call injection time t inj , we evaluate when the rate of increase of the particle Lorentz factor (averaged over c∆t/d e0 = 45) satisfies ∆γ/∆t ≥γ thr , and prior to this time the particle Lorentz factor was γ ≤ 4γ th0 ∼ 6. We take the thresholdγ thr 0.01 √ σ 0 γ th0 ω p0 , but we have verified that our identification of t inj is nearly the same when varyingγ thr around this value by up to a factor of three (the factor 0.01 is much lower than the typical collisionless reconnection rate [∼ 0.1, in units of the Alfvén speed], which is the appropriate reference scaling here, as showed in Comisso & Sironi (2018) and below). Once t inj is determined for the population of particles at hand, it is possible to explore the properties of the electromagnetic fields at the injection location.…”

Section: Particle Injection At Reconnecting Current Sheetsmentioning

confidence: 92%

“…Indeed, they showed that nonthermal energy distributions produced by driven turbulence converge to a system-sizeindependent power-law slope for sufficiently large domains. In order to explain the formation of nonthermal particle populations in magnetically-dominated turbulence, in Comisso & Sironi (2018) we analyzed selfconsistent particle trajectories from one of the PIC simulations, finding that most of the particles enter into the acceleration process through an injection phase that occurs at reconnecting current sheets which form selfconsistently in the turbulent system. However, we also found that this initial energy gain, mediated by reconnection, is relatively small.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The Interplay of Magnetically Dominated Turbulence and Magnetic Reconnection in Producing Nonthermal Particles

Comisso

Sironi

2019

ApJ

Self Cite

146

132

View full text Add to dashboard Cite

Magnetized turbulence and magnetic reconnection are often invoked to explain the nonthermal emission observed from a wide variety of astrophysical sources. By means of fully-kinetic 2D and 3D particle-in-cell simulations, we investigate the interplay between turbulence and reconnection in generating nonthermal particles in magnetically-dominated (or, equivalently, "relativistic") pair plasmas. A generic by-product of the turbulence evolution is the generation of a nonthermal particle spectrum with a power-law energy range. The power-law slope p is harder for larger magnetizations and stronger turbulence fluctuations, and it can be as hard as p 2. The Larmor radius of particles at the high-energy cutoff is comparable to the size l of the largest turbulent eddies. Plasmoid-mediated reconnection, which self-consistently occurs in the turbulent plasma, controls the physics of particle injection. Then, particles are further accelerated by stochastic scattering off turbulent fluctuations. The work done by parallel electric fields -naturally expected in reconnection layers -is responsible for most of the initial energy increase, and is proportional to the magnetization σ of the system, while the subsequent energy gain, which dominates the overall energization of high-energy particles, is powered by the perpendicular electric fields of turbulent fluctuations. The two-stage acceleration process leaves an imprint in the particle pitch-angle distribution: low-energy particles are aligned with the field, while the highest energy particles move preferentially orthogonal to it. The energy diffusion coefficient of stochastic acceleration scales as D γ ∼ 0.1σ(c/l)γ 2 , where γ is the particle Lorentz factor. This results in fast acceleration timescales t acc ∼ (3/σ) l/c. Our findings have important implications for understanding the generation of nonthermal particles in high-energy astrophysical sources.

show abstract

Section: Plasma Turbulencesupporting

confidence: 56%

Section: Particle Injection At Reconnecting Current Sheetsmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Interplay of Magnetically Dominated Turbulence and Magnetic Reconnection in Producing Nonthermal Particles

Comisso

Sironi

2019

ApJ

Self Cite

146

132

View full text Add to dashboard Cite

show abstract

“…As discussed in the Introduction (for more details, see also Appendix A), pairs are heated by an electric field E aligned with the local magnetic field, arising as the plasma becomes starved of free charges in intermittently formed current sheets. If the velocity of the plasma flowing into the reconnection layer is at least mildly relativistic, one expects the electric field to be of the same order of magnitude of the magnetic field, namely E ∼ B (in their PIC simulations, Comisso & Sironi (2018 found a typical E ∼ 0.1 × B). Pairs are therefore heated on a time scale…”

Section: Heating Ratementioning

confidence: 99%

Magnetic energy dissipation and origin of non-thermal spectra in radiatively efficient relativistic sources

Sobacchi

Lyubarsky

2019

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

The dissipation of turbulent magnetic fields is an appealing scenario to explain the origin of non-thermal particles in high-energy astrophysical sources. However, it has been suggested that the particle distribution may effectively thermalise when the radiative (synchrotron and/or Inverse Compton) losses are severe. Inspired by recent PIC simulations of relativistic turbulence, which show that electrons are impulsively heated in intermittent current sheets by a strong electric field aligned with the local magnetic field, we instead argue that in plasmas where the particle number density is dominated by the pairs (electron-positron and electronpositron-ion plasmas): (i) as an effect of fast cooling and of different injection times, the electron energy distribution is dn e /dγ ∝ γ −2 for γ γ heat (the Lorentz factor γ heat being close to the equipartition value), while the distribution steepens at higher energies; (ii) since the time scales for the turbulent fields to decay and for the photons to escape are of the same order, the magnetic and the radiation energy densities in the dissipation region are comparable; (iii) if the mass energy of the plasma is dominated by the ion component, the pairs with a Lorentz factor smaller than a critical one (of the order of the proton-to-electron mass ratio) become isotropic, while the pitch angle remains small otherwise. The outlined scenario is consistent with the typical conditions required to reproduce the Spectral Energy Distribution of blazars, and allows one to estimate the magnetisation of the emission site. Finally, we show that turbulence within the Crab Nebula may power the observed gamma-ray flares if the pulsar wind is nearly charge-separated at high latitudes.

show abstract

“…Strongly turbulent plasmas combine all the well known accelerators studied separately in the past (second order Fermi, unstable current sheets and turbulent shocks; see Karimabadi et al (2013Karimabadi et al ( , 2014. A systematic study of the transport properties of high energy particles in these mixed environments has only recently been started (see Vlahos et al (2004); Zank et al (2015); Matsumoto et al (2015); Vlahos et al (2016); Pisokas et al (2018); Garrel et al (2018); Comisso & Sironi (2018).…”

Section: Discussion and Summarymentioning

confidence: 99%

Superdiffusive stochastic Fermi acceleration in space and energy

Sioulas

Isliker

Vlahos

et al. 2019

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We analyze the transport properties of charged particles (ions and electrons) interacting with randomly formed magnetic scatterers (e.g. large scale local "magnetic fluctuations" or "coherent magnetic irregularities" usually present in strongly turbulent plasmas), using the energization processes proposed initially by Fermi in 1949. The scatterers are formed by large scale local fluctuations (δB/B ≈ 1) and are randomly distributed inside the unstable magnetic topology. We construct a 3D grid on which a small fraction of randomly chosen grid points are acting as scatterers. In particular, we study how a large number of test particles are accelerated and transported inside a collection of scatterers in a finite volume. Our main results are: (1) The spatial meansquare displacement < (∆r) 2 > inside the stochastic Fermi accelerator is superdiffusive, < (∆r) 2 >∼ t a r , with a r ∼ 1.2 − 1.6, for the high energy electrons with kinetic energy (W) larger than 1MeV, and it is normal (a r = 1) for the heated low energy (W < 10keV) electrons.(2) The transport properties of the high energy particles are closely related with the mean-free path that the particles travel in-between the scatterers (λ sc ). The smaller λ sc is, the faster the electrons and ions escape from the acceleration volume.(3) The mean displacement in energy < ∆W >∼ t a W is strongly enhanced inside the acceleration volume (a W = 1.5−2.5) for the high energy particles compared to the thermal low energy particles (a W = 0.4), i.e. high energy particles undergo an enhanced systematic gain in energy. (4) The mean-square displacement in energy < W 2 > is superdiffusive for the high energy particles and normal for the low energy, heated particles. (5) The acceleration time is also related with λ sc . (6) Electrons and ions have similar transport properties inside the stochastic Fermi accelerator.

show abstract

Particle Acceleration in Relativistic Plasma Turbulence

Cited by 179 publications

References 75 publications

The Interplay of Magnetically Dominated Turbulence and Magnetic Reconnection in Producing Nonthermal Particles

The Interplay of Magnetically Dominated Turbulence and Magnetic Reconnection in Producing Nonthermal Particles

Magnetic energy dissipation and origin of non-thermal spectra in radiatively efficient relativistic sources

Superdiffusive stochastic Fermi acceleration in space and energy

Contact Info

Product

Resources

About