Pitch-Angle Anisotropy Imprinted by Relativistic Magnetic Reconnection

Abstract

Radiation emitted by nonthermal particles accelerated during relativistic magnetic reconnection is critical for understanding the nonthermal emission in a variety of astrophysical systems, including blazar jets, black hole coronae, pulsars, and magnetars. By means of fully kinetic Particle-in-Cell (PIC) simulations, we demonstrate that reconnection-driven particle acceleration imprints an energy-dependent pitch-angle anisotropy and gives rise to broken power laws in both the particle energy spectrum and the pitch-angle anisotropy. The particle distributions depend on the relative strength of the non-reconnecting (guide field) versus the reconnecting component of the magnetic field ($B_g/B_0$) and the lepton magnetization (${\sigma }_0$). Below the break Lorentz factor ${\gamma }_0$ (injection), the particle energy spectrum is ultra-hard ($p_{<}<1$), while above ${\gamma }_0$, the spectral index $p_{>}$ is highly sensitive to $B_g/B_0$. Particles' velocities align with the magnetic field, reaching minimum pitch angles $\alpha$ at a Lorentz factor ${\gamma }_{\min \alpha }$ controlled by $B_g/B_0$ and ${\sigma }_0$. The energy-dependent pitch-angle anisotropy, evaluated through the mean of ${\sin }^2\alpha$ of particles at a given energy, exhibits power-law ranges with negative ($m_{<}$) and positive ($m_{>}$) slopes below and above ${\gamma }_{\min \alpha }$, becoming steeper as $B_g/B_0$ increases. The generation of anisotropic pitch angle distributions has important astrophysical implications. We address their effects on regulating synchrotron luminosity, spectral energy distribution, polarization, particle cooling, the synchrotron burnoff limit, emission beaming, and temperature anisotropy.

To appear in The Astrophysical Journal

References in corpus (31)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
• Fast TeV variability in blazars: jets in a jet
• Formation of Hard Power-laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection
• Simulations of relativistic collisionless shocks: shock structure and particle acceleration
• Blazar flares powered by plasmoids in relativistic reconnection
• General Theory of the Plasmoid Instability
• A Review of the 0.1 Reconnection Rate Problem
• Magnetic reconnection in the era of exascale computing and multiscale experiments
• Parallel electric fields are inefficient drivers of energetic electrons in magnetic reconnection
• Particle acceleration in the driven relativistic reconnection
• Fast particle acceleration in three-dimensional relativistic reconnection
• A Turbulent Model of Gamma-Ray Burst Variability
• Detection of Low-energy Breaks in Gamma-Ray Burst Prompt Emission Spectra
• Evidence of two spectral breaks in the prompt emission of gamma ray bursts
• Plasmoid Instability in Forming Current Sheets
• On the Value of the Reconnection Rate
• Pulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths
• Did Swift measure GRB prompt emission radii?
• Ion and Electron Acceleration in Fully Kinetic Plasma Turbulence
• The energetics of relativistic magnetic reconnection: ion-electron repartition and particle distribution hardness
• Particle Injection and Nonthermal Particle Acceleration in Relativistic Magnetic Reconnection
• Magnetic energy dissipation and gamma-ray emission in energetic pulsars
• Pitch Angle Anisotropy Controls Particle Acceleration and Cooling in Radiative Relativistic Plasma Turbulence
• Hard Synchrotron Spectra from Magnetically Dominated Plasma Turbulence
• Observations and modeling of the onset of fast reconnection in the solar transition region
• Optical/$\gamma$-ray blazar flare correlations: understanding the high-energy emission process using ASAS-SN and Fermi light curves
• A fully-kinetic model for orphan gamma-ray flares in blazars
• Synchrotron-Self-Compton radiation from magnetically-dominated turbulent plasmas in relativistic jets
• A Model for Nonthermal Particle Acceleration in Relativistic Magnetic Reconnection
• Ultrafast Variability in AGN Jets: Intermittency and Lighthouse Effect

Cited by in corpus (10)

• TeV neutrinos and hard X-rays from relativistic reconnection in the corona of NGC 1068
• Relativistic Magnetic Reconnection in Astrophysical Plasmas: A Powerful Mechanism of Nonthermal Emission
• Concurrent Particle Acceleration and Pitch-Angle Anisotropy Driven by Magnetic Reconnection: Ion-Electron Plasmas
• Intermittency and Dissipative Structures Arising from Relativistic Magnetized Turbulence
• Diffuse neutrino flux from relativistic reconnection in AGN coronae
• Scale Statistics of Current Sheets in Relativistic Collisionless Plasma Turbulence
• Non-thermal Synchrotron Emission and Polarization Signatures during Black Hole Flux Eruptions
• Spectropolarimetry of synchrotron radiation from relativistic electrons with anisotropic pitch-angle and various energy distributions
• Driven Collisionless Reconnection of Force-free Flux Tubes: From Onset to Coalescence
• Anisotropy and energy distribution of leptons and photons in radiative relativistic Alfvénic turbulence