Pulsar Wind Nebulae as Cosmic Pevatrons: A Current Sheet's Tale

Abstract

I outline, from a theoretical and somewhat personal perspective, significant features of Pulsar Wind Nebulae as Cosmic Accelerators. I discuss recent studies of Pulsar Wind Nebulae (PWNe). I pay special attention to the recently discovered gamma ray flares in the Crab Nebula's emission, focusing on the possibility, raised by the observations, that the accelerating electric field exceeds the magnetic field, suggesting that reconnection in the persistent current layer (a current sheet) plays a significant role in the behavior of this well studied Pevatron. I address the present status of the termination shock model for the particle accelerator that converts the wind flow energy to the observed non thermal particle spectra, concluding that it has a number of major difficulties related to the transverse magnetic geometry of the shock wave. I discuss recent work on the inferred pair outflow rates, which are in excess of those predicted by existing theories of pair creation, and use those results to point out that the consequent mass loading of the wind reduces the wind's bulk flow 4-velocity to the point that dissipation of the magnetic field in a pulsar's wind upstream of the termination shock is restored to life as a viable model for the solution of the "sigma problem". I discuss some suggestions that current starvation in the current flow supporting the structured ("striped") upstream magnetic field induces a transition to superluminal wave propagation. I show that current starvation probably does not occur, because those currents are carried in the current sheet separating there stripes rather than in the stripes themselves.

33 pages, 10 figures, 127 references. Based on a presentation at Workshop on Particle Acceleration in Cosmic Plasmas, May 16-20, 2011, Bern, Switzerland. In press in Space Science Reviews. Online publication available at http://www.springerlink.com/content/h625x370m373737u/

References in corpus (72)

• Time-dependent force-free pulsar magnetospheres: axisymmetric and oblique rotators
• The Evolution and Structure of Pulsar Wind Nebulae
• Switched magnetospheric regulation of pulsar spin-down
• Gamma-Ray Observations of a Giant Flare from The Magnetar SGR 1806-20
• The Axisymmetric Pulsar Magnetosphere
• The First Fermi Large Area Telescope Catalog of Gamma-ray Pulsars
• Particle Acceleration in Relativistic Magnetized Collisionless Electron-Ion Shocks
• Reconnection in a striped pulsar wind
• Discovery of Spatial and Spectral Structure in the X-Ray Emission from the Crab Nebula
• Gamma-ray flares from the Crab Nebula
• Dynamics of Earthquake Faults
• Discovery of Powerful Gamma-Ray Flares from the Crab Nebula
• The characteristics of millisecond pulsar emission: I. Spectra, pulse shapes and the beaming fraction
• Particle Acceleration in Relativistic Magnetized Collisionless Pair Shocks: Dependence of Shock Acceleration on Magnetic Obliquity
• Dissipation in Poynting-flux Dominated Flows: the Sigma-Problem of the Crab Pulsar Wind
• Modeling of Gamma-Ray Pulsar Light Curves with Force-Free Magnetic Field
• On the force-free magnetosphere of aligned rotator
• Fitting Pulsar Wind Tori
• Modeling the spectral evolution of PWNe inside SNRs
• Pulsar Polar Cap Heating and Surface Thermal X-Ray Emission II. Inverse Compton Radiation Pair Fronts
• Grand Unification in Neutron Stars
• Particle Acceleration and Magnetic Dissipation in Relativistic Current Sheet of Pair Plasmas
• Simulations of Axisymmetric Magnetospheres of Neutron Stars
• Axially symmetric relativistic MHD simulations of Pulsar Wind Nebulae in Supernova Remnants - On the origin of torus and jet-like features
• Gamma-ray Activity in the Crab Nebula: The Exceptional Flare of April 2011
• Detection of Pulsed Gamma Rays Above 100 GeV from the Crab Pulsar
• The termination shock in a striped pulsar wind
• Extreme particle acceleration in magnetic reconnection layers. Application to the gamma-ray flares in the Crab Nebula
• The Power of Axisymmetric Pulsar
• Reconnection-Powered Linear Accelerator and Gamma-Ray Flares in the Crab Nebula
• Three-dimensional numerical simulations of the pulsar magentoshere: Preliminary results
• Pulsar Wind Nebulae as Cosmic Pevatrons: A Current Sheet's Tale
• Revised Pulsar Spindown
• Pair Multiplicities and Pulsar Death
• Relativistic MHD Winds from Rotating Neutron Stars
• Simulated synchrotron emission from Pulsar Wind Nebulae
• The origin of peculiar jet-torus structure in the Crab nebula
• Observations of "wisps" in magnetohydrodynamic simulations of the Crab Nebula
• Constraints on Neutron Star Properties from X-ray Observations of Millisecond Pulsars
• Lepton Acceleration by Relativistic Collisionless Magnetic Reconnection
• Pulsed radiation from neutron star winds
• New Phase-coherent Measurements of Pulsar Braking Indices
• Polarization of high-energy pulsar radiation in the striped wind model
• On the efficiency of Fermi acceleration at relativistic shocks
• Polarization Changes of Pulsars due to Wave Propagation Through Magnetospheres
• A new mechanism for dissipation of alternating fields in Poynting dominated outflows
• Observations of the Crab pulsar between 25 GeV and 100 GeV with the MAGIC I telescope
• On the origin of variable gamma-ray emission from the Crab Nebula
• Very-high-energy gamma radiation associated with the unshocked wind of the Crab pulsar
• Pair cascades in the magnetospheres of strongly-magnetized neutron stars
• The Crab Nebula's Wisps in Radio and Optical
• Pulsar Pair Cascades in Magnetic Fields with Offset Polar Caps
• Time-dependence in Relativistic Collisionless Shocks: Theory of the Variable "Wisps" in the Crab Nebula
• An unified polar cap/striped wind model for pulsed radio and gamma-ray emission in pulsars
• On Fermi acceleration and MHD-instabilities at ultra-relativistic magnetized shock waves
• The Crab Nebula's Moving Wisps in Radio
• Twinkling pulsar wind nebulae in the synchrotron cut-off regime and the gamma-ray flares in the Crab Nebula
• Fermi Detection of the Pulsar Wind Nebula HESS J1640-465
• Pulsar Pair Cascades in a Distorted Magnetic Dipole Field
• Twelve-hour spikes from the Crab Pevatron
• On the physics of cold MHD winds from oblique rotators
• Characterization of the Crab Pulsar's Timing Noise
• VLBI imaging of a flare in the Crab Nebula: More than just a spot
• Particle acceleration in supernova-remnant shocks
• Dissipative Pulsar Magnetosphere
• High-energy pulses and phase-resolved spectra by inverse Compton emission in the pulsar striped wind - Application to Geminga
• Particle-In-Cell Simulations of a Nonlinear Transverse Electromagnetic Wave in a Pulsar Wind Termination Shock
• Superluminal waves in pulsar winds
• Stokes tomography of radio pulsar magnetospheres. I. Linear polarization
• A Tale of Two Current Sheets
• Soft X-rays from polar caps of the millisecond pulsar J0437--4715
• Pulsar Results with the Fermi Large Area Telescope

Cited by in corpus (83)

• Formation of Hard Power-laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection
• The surprising Crab pulsar and its nebula: A review
• Relativistic Shocks: Particle Acceleration and Magnetization
• Three-Dimensional Magnetohydrodynamic Simulations of the Crab Nebula
• Particle acceleration in axisymmetric pulsar current sheets
• Ab-Initio Pulsar Magnetosphere: Particle acceleration in Oblique Rotators and High-energy Emission Modeling
• Pulsar Wind Nebulae as Cosmic Pevatrons: A Current Sheet's Tale
• On the radiation mechanism of repeating fast radio bursts
• Physical Conditions in the Reconnection Layer in Pulsar Magnetospheres
• Solution to the Sigma-Problem of Pulsar Wind Nebulae
• Pulsar-Wind Nebulae: Recent Progress in Observations and Theory
• Pulsar wind nebulae with bow shocks: non-thermal radiation and cosmic ray leptons
• Electrodynamics of pulsar magnetospheres
• Progress in unveiling extreme particle acceleration in persistent astrophysical jets
• Gamma-ray flares in the Crab Nebula: A case of relativistic reconnection?
• Scaling of magnetic reconnection in relativistic collisionless plasmas
• Gamma-Ray and Hard X-Ray Emission from Pulsar-Aided Supernovae as a Probe of Particle Acceleration in Embryonic Pulsar Wind Nebulae
• Recent Progress on Particle Acceleration and Reconnection Physics during Magnetic Reconnectionin the Magnetically-dominated Relativistic Regime
• The Hunt for Pevatrons: The Case of Supernova Remnants
• Determining the Dominant Acceleration Mechanism during Relativistic Magnetic Reconnection in Large-scale Systems
• Effects of synchrotron cooling and pair production on collisionless relativistic reconnection
• Dissipation of the striped pulsar wind
• Magnetic Energy Release, Plasma Dynamics, and Particle Acceleration during Relativistic Turbulent Magnetic Reconnection
• Coherent emission in pulsars, magnetars and Fast Radio Bursts: reconnection-driven free electron laser
• Inclined Pulsar Magnetospheres in General Relativity: Polar Caps for the Dipole, Quadrudipole and Beyond
• Dissipation, Energy Transfer, and Spindown Luminosity in 2.5D PIC Simulations of the Pulsar Magnetosphere
• Magnetoluminescence
• Constraints on particle acceleration sites in the Crab Nebula from relativistic MHD simulations
• On the MHD modeling of the Crab Nebula radio emission
• Kinetic study of radiation-reaction-limited particle acceleration during the relaxation of unstable force-free equilibria
• Cosmic Ray Origins: An Introduction
• ASTRI Mini-Array Core Science at the Observatorio del Teide
• Pulsar Magnetospheres: Beyond the Flat Spacetime Dipole
• GeV-TeV Cosmic Ray Leptons in the Solar System from the Bow Shock Wind Nebula of the Nearest Millisecond Pulsar J0437-4715
• The imprint of pulsar parameters on the morphology of Pulsar Wind Nebulae
• Variable thermal energy injection from magnetar spin down as a possible cause of stripped-envelope supernova light-curve bumps
• Particle Acceleration during Magnetic Reconnection in a Low-beta Pair Plasma
• Origin of very high and ultra high energy cosmic rays
• Modelling Jets, Tori and Flares in Pulsar Wind Nebulae
• On the Radio Emitting Particles of the Crab Nebula: Stochastic Acceleration Model
• ALMA and NOEMA constraints on synchrotron nebular emission from embryonic superluminous supernova remnants and radio-gamma-ray connection
• PeV photon and neutrino flares from galactic gamma-ray binaries
• Modeling the γ-ray Pulsar Wind Nebulae population in our Galaxy
• Revised predictions of neutrino fluxes from Pulsar Wind Nebulae
• Intrabinary Shock Emission from Black Widows and Redbacks
• Reverberation of pulsar wind nebulae (II): Anatomy of the "thin-shell'' evolution
• Spatial Distribution of Pair Production over the Pulsar Polar Cap
• Relativistic Turbulence with Strong Synchrotron and Synchrotron-Self-Compton Cooling
• The variability of the Crab Nebula in radio: No radio counterpart to gamma-ray flares
• From young to old: the evolutionary path of Pulsar Wind Nebulae
• Relativistic Asymmetric Reconnection
• Probing the Birth of Post-merger Millisecond Magnetars by X-ray and Gamma-ray Emission
• A corrugated termination shock in pulsar wind nebulae?
• Detection of Small Flares from the Crab Nebula with Fermi-LAT
• Turbulent model of Crab nebula radiation
• The Critical Role of Collisionless Plasma Energization on the Structure of Relativistic Magnetic Reconnection
• On the Implications of Recent Observations of the Inner Knot in the Crab Nebula
• Solar wind discontinuity transformation at the bow shock
• Particle Acceleration in Pulsar Wind Nebulae: PIC modelling
• A Search for TeV Gamma-ray Emission from Pulsar Tails by VERITAS
• A fast current-driven instability in relativistic collisionless shocks
• Gamma-ray flux depressions of the Crab nebula in the high-energy range
• PeV proton acceleration in Gamma-ray Binaries
• Broad-Band High-Energy Emission of the Gamma-ray Binary System LS 5039: Spectral and Temporal Features using NuSTAR and Fermi Observations
• A Broadband Emission Model of Magnetar Wind Nebulae
• Rapid X-ray variations of the Geminga pulsar wind nebula
• Testing Models for the Shallow Decay Phase of Gamma-Ray Burst Afterglows with Polarization Observations
• Pulsar Wind Nebulae
• X-Ray and Optical Properties of Black Widows and Redbacks
• Introducing the HD+B model for pulsar wind nebulae: a hybrid hydrodynamics/radiative approach
• Electron acceleration at pulsar wind termination shocks
• Conditions for Relativistic Magnetic Reconnection under the Presence of Shear Flow and Guide Field
• Modeling Radio Circular Polarization in the Crab Nebula
• Test particles in relativistic resistive magnetohydrodynamics
• Relativistic astrospheres of gamma-ray binaries: modeling of non-thermal processes
• Enhanced particle acceleration in a pulsar wind interacting with a companion
• An extreme particle accelerator powered by pulsar PSR J1849-0001
• Scaling of Magnetic Dissipation and Particle Acceleration in ABC Fields
• The Eel Pulsar Wind Nebula: a PeVatron-Candidate Origin for HAWC J1826-128 and HESS J1826-130
• Particle dynamics governed by radiation losses in extreme-field current sheets
• How many VHE gamma-ray binaries with young pulsars can be observed?
• On the internal structure of the current sheet in the pulsar wind
• The Potential for Hadronic Particle Acceleration in Galactic Pulsar Wind Nebulae