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Abstract Relativistic magnetic turbulence has been proposed as a process for producing nonthermal particles in high-energy astrophysics. The particle energization may be contributed by both magnetic reconnection and turbulent fluctuations, but their interplay is poorly understood. It has been suggested that during magnetic reconnection the parallel electric field dominates the particle acceleration up to the lower bound of the power-law particle spectrum, but recent studies show that electric fields perpendicular to the magnetic field can play an important, if not dominant role. In this study, we carry out two-dimensional fully kinetic particle-in-cell simulations of magnetically dominated decaying turbulence in a relativistic pair plasma. For a fixed magnetization parameterσ0 = 20, we find that the injection energyεinjconverges with increasing domain size toεinj ≃ 10mec2. In contrast, the power-law index, the cut-off energy, and the power-law extent increase steadily with domain size. We trace a large number of particles and evaluate the contributions of the work done by the parallel (W∥) and perpendicular (W⊥) electric fields during both the injection phase and the postinjection phase. We find that during the injection phase, theW⊥contribution increases with domain size, suggesting that it may eventually dominate injection for a sufficiently large domain. In contrast, on average, both components contribute equally during the postinjection phase, insensitive to the domain size. For high energy (ε ≫ εinj) particles,W⊥dominates the subsequent energization. These findings may improve our understanding of nonthermal particles and their emissions in astrophysical plasmas.
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This content will become publicly available on May 6, 2027
The Effect of Inverse Compton Losses on Particle Acceleration in Three-dimensional Relativistic Reconnection
Abstract Relativistic magnetic reconnection is a key mechanism for dissipating magnetic energy and accelerating particles in astrophysics. In the absence of radiative cooling, recent particle-in-cell (PIC) simulations have shown that high-energy particles gain most of their energy in the upstream region, during a short-lived “free phase” where they meander between the two sides of the layer; when they get captured/trapped by the downstream flux ropes, they undergo a “trapped phase,” where no significant energization occurs. Here, we perform a suite of 3D PIC simulations of relativistic reconnection, including inverse Compton (IC) losses in the weakly cooled regime in which the radiation-reaction-limited Lorentz factorγradexceeds the magnetizationσ. We show that electron cooling losses do not appreciably alter the reconnection rate, the structure of the layer, and the physics of particle acceleration in the free phase, so the spectrum of free electrons isdNfree/dγ ∝ γ−1, as in the uncooled case. The spectrum of trapped electrons above the cooling breakγcool(in the rangeγcool < γ < γrad) isdN/dγ ∝ γ−3, steeper than the scalingdN/dγ ∝ γ−2of uncooled simulations. This confirms that no significant particle energization occurs during the trapped phase. Our results validate the model by Zhang et al. for particle acceleration in 3D relativistic reconnection, and imply that radiative emission models of reconnection-powered astrophysical sources should employ a two-zone structure that differentiates between free, rapidly accelerating particles and trapped, passively cooling particles.
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- PAR ID:
- 10695872
- Publisher / Repository:
- The Astrophysical Journal
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 1002
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 181
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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