Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session CO06: Astrophysical Jets and FlaresOn Demand
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Chair: Seth Dorfman, Space Science Institute Room: Rooms 310-311 |
Monday, November 8, 2021 2:00PM - 2:12PM |
CO06.00001: First-principles simulations of collisionless accretion onto black holes: dynamics and flares Alexander A Philippov Accretion flows onto primary targets of the Event Horizon Telescope, M87* and SgrA*, consist of collisionless plasmas. It is yet unknown how microphysical instabilities in these plasmas affect the dynamics of the flow, and how non-thermal particles are produced during observed spectacular multi-wavelength flares. In this talk I will show results of first-principles two-dimensional general-relativistic particle-in-cell simulations which address these fundamental questions. Large separation of microscopic (ion gyroradius) and macroscopic (black hole event horizon) scales in the simulation allows to probe the importance of mirror and firehose instabilities during the quiescent accretion, as well as the dynamics of magnetic reconnection and creation of electron-positron pair plasma in the flaring state. |
Monday, November 8, 2021 2:12PM - 2:24PM |
CO06.00002: Magnetic Energy Release, Plasma Dynamics and Particle Acceleration in Relativistic Turbulent Magnetic Reconnection Fan Guo, Xiaocan Li, William S Daughton, Hui Li, Patrick F Kilian, Yi-Hsin Liu, Qile Zhang, Haocheng Zhang Relativistic magnetic reconnection is thought to be a primary process for explosive energy release and particle acceleration. A less explored issue is the consequence of 3D dynamics, where turbulent structures are generated as various types of instabilities develop. We present 3D fully-kinetic simulations of relativistic turbulent magnetic reconnection (RTMR) in positron-electron plasmas with system domains much larger than kinetic scales. Our simulations start from a force-free current sheet with several modes of long wavelength magnetic perturbations, which drive additional turbulence in the reconnection region. The current layer breaks up and the reconnection region quickly evolves into a turbulent layer filled with coherent structures like flux ropes and current sheets. We find that plasma dynamics in RTMR is vastly different from their 2D counterparts. The flux ropes evolve rapidly after their generation, and can be disrupted due to the secondary kink instability. We present analysis on reconnection generated turbulence. Meanwhile, nonthermal particle acceleration and energy-release time scale are fast and do not strongly depend on the turbulence amplitude. The main acceleration mechanism is a Fermi-like acceleration process supported by the motional electric field. |
Monday, November 8, 2021 2:24PM - 2:36PM |
CO06.00003: Black hole flares: ejection of accreted magnetic flux regulated by plasmoid-dominated reconnection Bart Ripperda Magnetic reconnection is conjectured to power bright and rapid flares originating from the inner magnetospheres in accreting black holes. We conduct extreme resolution three-dimensional general relativistic magnetohydrodynamics simulations of a magnetically arrested black hole accretion disk showing that a transient, non-axisymmetric, highly magnetized magnetosphere can form in the inner 10 Schwarzschild radii accompanied by a drop in mass accretion rate. A macroscopic equatorial current sheet establishes in the magnetosphere, extending from the event horizon to the accretion disk. Magnetic flux is expelled from the horizon through magnetic reconnection in this current sheet fed by the highly magnetized surrounding plasma in the black hole jet. Reconnection heats plasmoids, or flux tubes, to temperatures proportional to the magnetization in the jet. The hot flux tubes that are expelled from the exhaust of the reconnection layer can power bright TeV flares as observed from M87. The timescales of the flare are directly determined by the reconnection rate in the plasmoid-dominated regime. The flux tubes can orbit in the disk for an orbital period, as low-density hot spots. |
Monday, November 8, 2021 2:36PM - 2:48PM |
CO06.00004: Relativistic reconnection-powered high-energy astrophysical flares: strong magnetization dependence and applications to X-ray flares in Sgr A* Dmitri A Uzdensky Relativistic collisionless magnetic reconnection is an attractive candidate for explaining nonthermal particle acceleration powering intense high-energy flares in a variety of astrophysical objects. Fully kinetic numerical simulations indicate that the nonthermal power-law index of the reconnection-generated relativistic particle spectrum f(γ) depends on the ambient plasma’s (hot) magnetization σ-parameter (the ratio of magnetic and relativistic plasma enthalpies), with higher σ resulting in harder spectra. In particular, there is a critical value of σ, of order of a few, above which the spectrum becomes harder than f(γ)~γ-2, so that most of the released energy goes to the most energetic particles near the power law’s high-energy cutoff. We show that below this σ threshold, the energy share of the most energetic nonthermal particles --- and hence the brightness of the high-energy flares they emit, especially within a fixed observed spectral band --- becomes a very strong function of σ and hence of the reconnecting magnetic field strength. This strong sensitivity to the ambient magnetization conditions has important implications for assessing the viability of the synchrotron scenario for the X-ray flares observed from our Galactic Center black hole Sgr-A*. |
Monday, November 8, 2021 2:48PM - 3:00PM |
CO06.00005: Time-dependent screening of the electric field in pulsar discharges and its implications for coherent radio emission Elizabeth A Tolman, Alexander A Philippov, Andrey Timokhin Pulsars produce coherent radio emission, the source of which has remained enigmatic. Recent computational work suggests this emission may be produced in nonstationary pair plasma discharges in the pulsar polar cap, where the pulsar electric field is screened by newly-produced electron-positron pairs, leading to the production of plasma waves which escape from the magnetosphere as radio emission (Philippov et al., Physical Review Letters 2020). In this talk, we present the physical principles governing the evolution of wave energy in the polar cap's time-dependent, relativistic, collisionless pair plasma, for both linear waves and nonlinear waves. These principles are then used to analytically determine the change in the pulsar polar cap electric field amplitude as it is screened. Finally, we discuss the implications of this model for coherent radio emission and the interpretation of pulsar observations. |
Monday, November 8, 2021 3:00PM - 3:12PM |
CO06.00006: Relativistic Shear Flows and the Gamma-Ray Emission of GW170817 Edison P Liang, jacob spisak, wen fu, markus boettcher We present an analysis of the radiation characteristics of kinetic shear boundary layers created by relativistic |
Monday, November 8, 2021 3:12PM - 3:24PM |
CO06.00007: Intrinsic Gravitational Modes Sustained by (GR) Gravitational Wave Emitters Renato Spigler, Bruno Coppi, Bamandas Basu Black holes resulting from stellar collapse had been conjectured [1] to be imbedded in plasma structures since early systematic theory efforts were undertaken. The conjecture has been confirmed later by the observations on both galactic and (extra galactic) massive black holes. (GR) Gravitational Wave emitters that include BH binaries imbedded in plasma disks are shown to sustain the parallel emergence of Intrinsic Gravitational Modes [2] that rotate (toroidally) with the same frequency as the rotation frequency Ωob of the binary with which they are associated. For binaries with equal mass BH’s the mode frequencies are equal to a multiple of 2Ωob. The lowest frequency (2Ωob) modes are ballooning (standing) in the vertical direction and can be driven linearly, albeit with relatively low amplitudes, by the force associated with the time-dependent component of the gravitational potential. The higher frequency modes can be represented as a combination of ballooning structures and a helical (vertically) propagating wave with a frequency close to the ion-sound frequency, referring to plasmas with electron temperatures considerably higher than those of the nuclei. |
Monday, November 8, 2021 3:24PM - 3:36PM |
CO06.00008: Ejected Beamed Pairs of "Gravitational Phonons" from Gravitational Waves Emitters Bruno Coppi Beam ejected pairs of “Gravitational Phonons” are found as double helix plasma structures emerging from disks in which (GR) gravitational wave emitters (e.g., black hole binaries before their collapse) can be expected to be imbedded. The pair components [1] are a combination of ballooning modes and vertically propagating ion sound helical waves considering disk electron temperatures well in excess of those of the nuclei. The toroidal rotation frequency is, for both modes, equal to the rotating frequency Ωob of binaries involving, for simplicity, two equal BH masses. Then, the modes’ frequencies are multiple of 2Ωob, and differ by 2Ωob, both waves propagating in the same vertical direction with equal wave numbers. The nonlinear coupling of the pair constituents is driven by the periodic vertical force associated with the time-dependent tridimensional component of the relevant gravitational potential. Clearly, the collimation of the ejected double helix can be undermined by encounters with regions of rarefied plasma turbulence. |
Monday, November 8, 2021 3:36PM - 3:48PM |
CO06.00009: Nonlinear instability in relativistic pair beams: magnetic field amplification and electron-positron asymmetry John R Peterson, Siegfried Glenzer, Frederico Fiuza Relativistic electron-positron pair beams are often produced in gamma-ray bursts and blazar jets through photon-photon collisions. These beams can become unstable to plasma microinstabilities, however when the beam is less dense than the ambient medium, these instabilities saturate at small spatial scales and only a small fraction of the beam kinetic energy is converted to magnetic fields. We present a new nonlinear instability which can grow after saturation of the Weibel instability and increases the magnetic field strength and spatial scale by orders of magnitude, allowing magnetic fields to reach near-equipartition levels even at very low beam densities. In addition, the instability leads to an energy asymmetry between the beam species; the beam electrons drive the formation of magnetic-field-filled cavities in which they are inductively decelerated, while the positrons are repelled and flow through the cavity walls. This preferential deceleration of electrons can have important consequences for matter-antimatter asymmetries in astrophysical sources. In addition, in GRBs, the nonlinear instability may dominate magnetic field amplification upstream of relativistic shocks with important consequences for particle acceleration and radiation emission. |
Monday, November 8, 2021 3:48PM - 4:00PM |
CO06.00010: PIC simulations and spectral analysis of plasma with interpenetrating beams Michael C Sitarz, Mikhail V Medvedev, Alexander A Philippov Plasma with interpenetrating beams is known to exhibit instabilities such as the filamentation and two-stream instabilities. Beam-plasma systems are ubiquitous in high-energy-density environments, e.g., in laser-produced plasmas and astrophysical sources, such as in collisionless shocks of cosmic explosions -- gamma-ray bursts and supernovae. Here we investigate the case of a collisionless, unmagnetized system with relativistic counter-streaming beams with PIC simulations. We present the spectral analysis of the system as it evolves. We discuss the spectrum, temporal and angular distribution of the generated plasma modes. |
Monday, November 8, 2021 4:00PM - 4:12PM |
CO06.00011: New Results for Collisionless Damping in Relativistic Plasmas Jeff W Banks, Richard L Berger, Thomas D Chapman, William Arrighi, Jennifer K Gorman New theoretical and computational results for Landau damping are presented. The plasma dispersion function is solved to machine precision using direct line integration in the complex plane, in combination with an analytic evaluation of the residue to account for the deformation along the Landau contour. The approach is generic in that it applies to arbitrary distribution functions, and here we focus on Langmuir waves. As is well-known, we confirm that the Landau root becomes increasingly undamped as the plasma becomes hotter, and furthermore show that the Landau root ceases to exist for sufficiently relativistic plasmas. We also confirm past findings of undamped modes with superluminal phase velocities, unique to a relativistic treatment of the dispersion function, and offer new insights into their properties. |
Monday, November 8, 2021 4:12PM - 4:24PM |
CO06.00012: Dissipative Magnetohydrodynamics for Non-Resistive Relativistic Plasmas: A flux-conservative formulation with stiff relaxation Elias R Most, Jorge Noronha Based on a 14-moment closure for non-resistive viscous plasmas, we |
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