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Abstract:
We examine the possible role of turbulence in feeding the emission of gamma-ray bursts (GRBs). Turbulence may
develop in a GRB jet as the result of hydrodynamic or current-driven instabilities. The jet carries dense radiation
and the turbulence cascade can be damped by Compton drag, passing kinetic fluid energy to photons through
scattering. We identify two regimes of turbulence dissipation: (1) “Viscous”—the turbulence cascade is Comptondamped
on a scale ℓdamp greater than the photon mean free path ℓ★. Then turbulence energy is passed to photons via
bulk Comptonization by smooth shear flows on scale ℓ★< ℓdamp. (2) “Collisionless”—the cascade avoids Compton
damping and extends to microscopic plasma scales much smaller than ℓ★. The collisionless dissipation energizes
plasma particles, which radiate the received energy; how the dissipated power is partitioned between particles
needs further investigation with kinetic simulations. We show that the dissipation regime switches from viscous to
collisionless during the jet expansion, at a critical value of the jet optical depth, which depends on the amplitude of
turbulence. Turbulent GRB jets are expected to emit nonthermal photospheric radiation. Our analysis also suggests
revisions of turbulent Comptonization in black hole accretion disks discussed in previous works.
