Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session NM09: Mini-Conference on Reconnection: AstrophysicsLive
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Chair: Adam Stanier, LANL |
Wednesday, November 11, 2020 9:30AM - 10:00AM Live |
NM09.00001: Relativistic magnetic reconnection in plasmas around black holes and neutron stars Alexander Philippov In this talk I will review the growing evidence of the importance of relativistic magnetic reconnection in powering observed emission from black holes and neutron stars. I will focus on the role of reconnection in accretion flows and jets from black holes and in magnetospheres of pulsars, magnetars and binary neutron stars before the merger. [Preview Abstract] |
Wednesday, November 11, 2020 10:00AM - 10:25AM Live |
NM09.00002: Magnetic reconnection in pulsar magnetospheres, winds and nebulae Benoit Cerutti Pulsars blow ultra-magnetized relativistic winds loaded with electron-positron pairs created and launched in the magnetospheric regions. A generic feature of pulsar winds is a large-scale oscillating current sheet, or striped wind, forming where the magnetic field polarity reverses, thus providing an ideal environment to study magnetic reconnection in the relativistic, collisionless and radiative regime. Reconnection in the innermost parts of the wind is thought to power the observed high-energy pulsed emission from pulsars. Recent global particle-in-cell simulations suggest that reconnection proceeds in the plasmoid-dominated regime and consumes the field until the complete dissipation of the striped wind. At the wind termination shock, the remaining magnetic energy may be dissipated via turbulent reconnection, which may power the bright synchrotron nebula surrounding pulsars. [Preview Abstract] |
Wednesday, November 11, 2020 10:25AM - 10:50AM Live |
NM09.00003: Magnetic Reconnection under Extreme Astrophysical Plasma Conditions Dmitri Uzdensky, John Mehlhaff, Gregory Werner, Mitchell Begelman Magnetic reconnection is a key fundamental plasma-physical process operating in many astrophysical systems and responsible for sudden and often violent release of accumulated magnetic energy, powering spectacular X-ray and gamma-ray flares. In many of the most enigmatic relativistic high-energy astrophysical systems (those associated with neutron stars and black holes) the plasma conditions are so extreme that exotic physics effects --- e.g., strong interaction of plasma with radiation and QED processes such as pair creation --- need to be included self-consistently in the plasma description. These effects modify reconnection dynamics, energetics, nonthermal particle acceleration, and observable radiative signatures. They thus necessitate the exploration of a new frontier in plasma astrophysics --- radiative magnetic reconnection. In this talk I will present a systematic overview of extreme radiative magnetic reconnection, with a focus on an orderly classification of the different physical parameter regimes. I will also discuss astrophysical applications of radiative reconnection with concrete examples drawn from modern high-energy astrophysics research.\\In collaboration with: John Mehlhaff, University of Colorado, Boulder; Gregory Werner, University of Colorado, Boulder; Mitchell Begelman, JILA and University of Colorado, Boulder [Preview Abstract] |
Wednesday, November 11, 2020 10:50AM - 11:15AM Live |
NM09.00004: The Dominant Acceleration Mechanism and Formation of Power-law Particle Energy Spectra in Spontaneous, Turbulent and Forced Relativistic Magnetic Reconnection Fan Guo, Xiaocan Li, Yingchao Lu, Hui Li, William Daughton, Patrick Kilian, Yi-Hsin Liu While a growing body of research indicates that relativistic magnetic reconnection is a prodigious source of particle acceleration in high-energy astrophysical systems, the primary acceleration mechanism and formation of power-law energy spectra remain controversial. We have developed a series of fully kinetic simulations and theoretical analysis for discerning the primary acceleration mechanism. Our analysis statistically evaluates the acceleration of a large number of particles, and therefore can distinguish contributions of different acceleration mechanisms without bias. We apply these analyses to several applications including spontaneous reconnection, 3D relativistic turbulent magnetic reconnection, and forced reconnection when current sheets cross a shock. We show consistently that relativistic magnetic reconnection in the low guide field regime accelerates particles to high energy via Fermi acceleration in relativistic flows generated during reconnection. We further provide analytical derivations for the development of power-law energy spectra. The analysis shows the critical roles of particle injection and Fermi acceleration. The escape term does not lead to power-laws, but it is important in determining the eventual shape of the spectrum.\\In collaboration with: Xiaocan Li, Dartmouth College; Yingchao Lu, Los Alamos Natl Lab; Hui Li, William Daughton, Los Alamos Natl Lab; Patrick Kilian, Los Alamos Natl Lab; Yi-Hsin Liu Dartmouth College [Preview Abstract] |
Wednesday, November 11, 2020 11:15AM - 11:40AM Live |
NM09.00005: Radiative Relativistic Reconnection Lorenzo Sironi Relativistic jets of blazars and magnetized coronae of highly accreting black holes routinely display non-thermal emission signatures, including fast and bright flares of high-energy emission. Yet, the “engine” responsible for accelerating the emitting particles to ultra-relativistic energies is still unknown. With fully-kinetic particle-in-cell (PIC) simulations, we study the physics of relativistic magnetic reconnection — where the magnetic energy of annihilating field lines is even larger than the particle rest mass energy — in the radiative regime where the particle cooling time is shorter than the lifetime of the system. We show that radiative relativistic reconnection offers an intriguing explanation for (1) high-energy flares in blazar jets, and associated rotations in the optical polarization vector; and (2) the hard-state spectra of black hole X-ray binaries and Active Galactic Nuclei. [Preview Abstract] |
Wednesday, November 11, 2020 11:40AM - 11:58AM Live |
NM09.00006: Role of magnetic reconnection in accelerating particles in magnetically dominated turbulent plasmas Luca Comisso, Lorenzo Sironi Magnetic reconnection and magnetized turbulence are often invoked to explain the nonthermal emission observed from a wide variety of astrophysical sources. By means of fully-kinetic particle-in-cell simulations of magnetically dominated pair plasmas, we investigate the interplay between magnetic reconnection and turbulence in generating nonthermal particle distributions with a power-law high energy range. Plasmoid-mediated reconnection, which self-consistently occurs in the turbulent plasma, controls the initial stage of particle acceleration. Then, particles are further accelerated by stochastic scattering off large-scale turbulent fluctuations. The work done by parallel electric fields associated with magnetic reconnection layers is responsible for most of the initial energy increase, and is proportional to the magnetization 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 energy diffusion coefficient of stochastic acceleration scales as the second power of the particle Lorentz factor and linearly with respect to the magnetization parameter. The resulting acceleration timescale is very fast for highly magnetized systems. [Preview Abstract] |
Wednesday, November 11, 2020 11:58AM - 12:16PM Live |
NM09.00007: Power-law index of energy spectrum in magnetically dominated systems Xiaocan Li, Fan Guo, Yi-Hsin Liu, Patrick Kilian, Hui Li Fermi mechanisms accelerate particles to develop power-law energy spectra when the system is sufficiently large for the regions of particle injection, acceleration, and escape to be well separated from each other. This model has successfully explained the power-law formation in diffusive shock acceleration. Using a series of kinetic simulations, we demonstrate that this model can also explain the power-law spectra formed during magnetic energy dissipation by magnetic reconnection or turbulence in magnetically dominated plasmas. The simulations use periodic domains but particles can still escape from the acceleration regions, which only occupies a fraction of a large system. Using tracer particles, particle acceleration and escape rates are accurately calculated. The modeled power-law index obtained from a transport equation in energy matches well with the simulation results. This shows that the classical Fermi-type acceleration theory is still providing new insights into the results of kinetic simulations. [Preview Abstract] |
Wednesday, November 11, 2020 12:16PM - 12:34PM Live |
NM09.00008: Nature of Fluctuations and Turbulence in 3D Reconnection Hui Li, Liping Yang, Senbei Du, Xiaocan Li, Fan Guo Recent 3D magnetic reconnection simulations have revealed the critical role of fluctuations and turbulence in regulating the reconnection process as well as their influence on particle transport. The origin of these fluctuations can be both externally driven and self-generated. The self-generated fluctuations can be from instabilities such as tearing and Kelvin-Helmholtz, and collisions of outflows from 3D reconnection. Such processes tend to drive fluctuations on small or intermediate scales, from which both forward and inverse cascade can produce a broad turbulence like spectrum. We will describe these processes using both 3D MHD and PIC simulations and quantify the nature of such fluctuations. Implications for particle transport will be discussed as well. [Preview Abstract] |
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