Prof Dmitri Uzdensky: Publications

Bright Gamma-Ray Flares Powered by Magnetic Reconnection in QED-strength Magnetic Fields

The Astrophysical Journal American Astronomical Society 870:1 (2019) 49-49

Authors:

KM Schoeffler, T Grismayer, D Uzdensky, RA Fonseca, LO Silva

Abstract:

Abstract Strong magnetic fields in the magnetospheres of neutron stars (NSs) (especially magnetars) and other astrophysical objects may release their energy in violent, intense episodes of magnetic reconnection. While reconnection has been studied extensively, the extreme field strength near NSs introduces new effects: radiation cooling and electron–positron pair production. Using massively parallel particle-in-cell simulations that self-consistently incorporate these new radiation and quantum-electrodynamic effects, we investigate relativistic magnetic reconnection in the strong-field regime. We show that reconnection in this regime can efficiently convert magnetic energy to X-ray and gamma-ray radiation and thus power bright, high-energy astrophysical flares. Rapid radiative cooling causes strong plasma and magnetic field compression in compact plasmoids. In the most extreme cases, the field can approach the quantum limit, leading to copious pair production.

System-size Convergence of Nonthermal Particle Acceleration in Relativistic Plasma Turbulence

The Astrophysical Journal Letters American Astronomical Society 867:1 (2018) L18-L18

Authors:

Vladimir Zhdankin, Dmitri A Uzdensky, Gregory R Werner, Mitchell C Begelman

Abstract:

Abstract We apply collisionless particle-in-cell simulations of relativistic pair plasmas to explore whether driven turbulence is a viable high-energy astrophysical particle accelerator. We characterize nonthermal particle distributions for varying system sizes up to L/2π�� e0 = 163, where L/2π is the driving scale and �� e0 is the initial characteristic Larmor radius. We show that turbulent particle acceleration produces power-law energy distributions that, when compared at a fixed number of large-scale dynamical times, slowly steepen with increasing system size. We demonstrate, however, that convergence is obtained by comparing the distributions at different times that increase with system size (approximately logarithmically). We suggest that the system-size dependence arises from the time required for particles to reach the highest accessible energies via Fermi acceleration. The converged power-law index of the energy distribution, α ≈ 3.0 for magnetization σ = 3/8, makes turbulence a possible explanation for nonthermal spectra observed in systems such as the Crab Nebula.

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