Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session L08: Astrophysical Particle Acceleration
3:30 PM–5:06 PM,
Sunday, April 14, 2019
Sheraton
Room: Governor's Square 10
Sponsoring
Unit:
DAP
Chair: Louis Strigari, Texas A&M University
Abstract: L08.00004 : Direct Numerical Demonstration of Diffusive Nonthermal Particle Acceleration in Particle-in-Cell Simulations of Kinetic Turbulence in Relativistic Pair Plasmas*
4:06 PM–4:18 PM
View Presentation Abstract
Presenter:
Kai W Wong
(University of Colorado, Boulder)
Authors:
Kai W Wong
(University of Colorado, Boulder)
Vladimir V Zhdankin
(Princeton University)
Dmitri A Uzdensky
(University of Colorado, Boulder)
Gregory R Werner
(University of Colorado, Boulder)
Mitchell Begelman
(JILA)
Nonthermal particle acceleration (NTPA) is ubiquitous in high-energy astrophysics, as evidenced by cosmic rays and the emission spectra of pulsar wind nebulae and active galactic nuclei. Most analytical models of NTPA posit diffusive Fermi acceleration described by a Fokker-Planck (FP) advection-diffusion equation in momentum space. We test the applicability of the FP framework directly in kinetic particle-in-cell simulations of driven magnetized turbulence in relativistic pair plasma. By statistically analyzing the motion of almost a million tracked particles, we confirm the diffusive nature of turbulent NTPA and measure the FP energy diffusion (D) and advection (A) coefficients as functions of particle energy γmec2. We find that D(γ) is proportional to γ2 in the high-energy nonthermal tail, in line with 2nd-order Fermi acceleration theory, but has a much shallower scaling of about γ2/3 at lower energies, while A tends to pull particles towards the peak of the distribution. We also explore the effects of magnetization. Our results provide strong support for the FP picture of turbulent NTPA, thereby enhancing our understanding of space, solar, and astrophysical plasmas.
*Work supported by NASA and NSF.
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