Crab Flares Due to Turbulent Dissipation of the Pulsar Striped Wind

Zrake, Jonathan

doi:10.3847/0004-637x/823/1/39

Cited by 34 publications

(25 citation statements)

References 62 publications

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“…Our model is similar to the "blob" picture proposed by Zrake (2016). In this scenario, the GeV synchrotron emission observed during the flares is produced by magnetically-confined populations of relativistic electrons that are processed via particle acceleration, losses, and escape occurring in the active reconnection region surrounding the pulsar-wind termination shock.…”

Section: Particle Transport Formalismsupporting

confidence: 78%

Time-dependent Electron Acceleration in Pulsar Wind Termination Shocks: Application to the 2007 September Crab Nebula Gamma-Ray Flare

Kroon

Becker

Finke

2019

ApJ

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In 2007 September, the Crab Nebula exhibited a bright γ-ray flare in the GeV energy range that was detected by AGILE. The observed emission at 160 MeV indicates that the radiating electrons had energies above the classical synchrotron radiation-reaction limit, thus presenting a serious challenge to classical models for electron acceleration in astrophysical environments. In this paper, we apply our recently developed time-dependent self-similar analytical model describing electrostatic acceleration in the explosive reconnection region around the pulsar wind termination shock to the 2007 September flare. This event was unique in that it displayed both long-duration "wave" and short-duration "sub-flare" features. The unusual temporal variation makes this flare an especially interesting test for our model. We demonstrate that our model can reproduce the time-dependent γ-ray spectrum for this event, as well as the associated γ-ray light curve, obtained by integrating the spectrum for photon energies ≥ 100 MeV. This establishes that our time-dependent electrostatic acceleration model can explain both wave and sub-flare transients, which lends further support to the theoretical framework we have developed. We also further examine the validity of the self-similar electric and magnetic field evolution implied by our model. We conclude that strong electrostatic acceleration driven by shock-induced magnetic reconnection is able to power the Crab Nebula γ-ray flares by energizing the electrons on sub-Larmor timescales.

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Section: Particle Transport Formalismsupporting

confidence: 78%

Time-dependent Electron Acceleration in Pulsar Wind Termination Shocks: Application to the 2007 September Crab Nebula Gamma-Ray Flare

Kroon

Becker

Finke

2019

ApJ

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“…The second possibility is that, the pulsar wind is initially striped with a wavelength λ w much shorter than the termination shock radius r s , e.g., λ w =10 9 cm while r s =3×10 17 cm for the Crab. These stripes-small scale fluctuations-continue to go through inverse cascade, forming larger and larger flux ropes, eventually reaching a large enough scale that is relevant for the acceleration of PeV particles (Zrake 2016). Another possibility involves the polar jet, which has relatively high magnetization and is kink unstablesuggesting that it possesses free magnetic energy.…”

Section: Discussionmentioning

confidence: 99%

Kinetic Study of Radiation-Reaction-Limited Particle Acceleration During the Relaxation of Unstable Force-Free Equilibria

Yuan

Nalewajko

Zrake

et al. 2016

ApJ

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Many powerful and variable gamma-ray sources, including pulsar wind nebulae, active galactic nuclei and gammaray bursts, seem capable of accelerating particles to gamma-ray emitting energies efficiently over very short timescales. These are likely due to the rapid dissipation of electromagnetic energy in a highly magnetized, relativistic plasma. In order to understand the generic features of such processes, we have investigated simple models based on the relaxation of unstable force-free magnetostatic equilibria. In this work, we make the connection between the corresponding plasma dynamics and the expected radiation signal, using 2D particle-incell simulations that self-consistently include synchrotron radiation reactions. We focus on the lowest order unstable force-free equilibrium in a 2D periodic box. We find that rapid variability, with modest apparent radiation efficiency as perceived by a fixed observer, can be produced during the evolution of the instability. The "flares" are accompanied by an increased polarization degree in the high energy band, with rapid variation in the polarization angle. Furthermore, the separation between the acceleration sites and the synchrotron radiation sites for the highest energy particles facilitates acceleration beyond the synchrotron radiation reaction limit. We also discuss the dynamical consequences of theradiation reaction, and some astrophysical applications of this model. Our current simulations with numerically tractable parameters are not yet able to reproduce the most dramatic gamma-ray flares, e.g., from theCrab Nebula. Higher magnetization studies are promising and will be carried out in the future.

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“…the Crab Nebula (Tavani et al 2011;Abdo et al 2011). The development of both turbulence and turbulent reconnection of magnetic fields have been observed in numerical simulations of the pulsar striped wind, e.g., Zrake (2016).…”

Section: Physical Origin Of a Broken Power-lawmentioning

confidence: 99%

On the Broadband Synchrotron Spectra of Pulsar Wind Nebulae

Klingler

Kargaltsev

Zhang

2019

ApJ

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As shown by broad-band observations, pulsar wind nebulae (PWNe) are characterized by a broken power-law spectrum of synchrotron emission. Based on the modern magnetohydrodynamic (MHD) turbulence theories, we investigate the re-acceleration of electrons in the PWN through the adiabatic stochastic acceleration (ASA), which arises from fundamental dynamics of MHD turbulence. The ASA acts to flatten the injected energy spectrum of electrons at low energies, while synchrotron cooling results in a steep spectrum of electrons at high energies. Their dominance in different energy ranges leads to a flat radio spectrum (F ν ) and a steep X-ray spectrum. Our analytical spectral shapes generally agree well with the observed synchrotron spectra of radioand X-ray-bright PWNe. The spectral break corresponding to the balance between the ASA and synchrotron losses provides a constraint on the acceleration timescale of the ASA and the magnetic field strength in the PWN.

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Crab Flares Due to Turbulent Dissipation of the Pulsar Striped Wind

Cited by 34 publications

References 62 publications

Time-dependent Electron Acceleration in Pulsar Wind Termination Shocks: Application to the 2007 September Crab Nebula Gamma-Ray Flare

Time-dependent Electron Acceleration in Pulsar Wind Termination Shocks: Application to the 2007 September Crab Nebula Gamma-Ray Flare

Kinetic Study of Radiation-Reaction-Limited Particle Acceleration During the Relaxation of Unstable Force-Free Equilibria

On the Broadband Synchrotron Spectra of Pulsar Wind Nebulae

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