The effects of sub-shells in highly magnetized relativistic flows

Abstract

Astrophysical sources of relativistic jets or outflows, such as gamma-ray bursts (GRBs), active galactic nuclei (AGN) or micro-quasars, often show strong time variability. Despite such impulsive behavior, most models of these sources assume a steady state for simplicity. Here I consider a time-dependent outflow that is initially highly magnetized and divided into many well-separated sub-shells, as it experiences impulsive magnetic acceleration and interacts with the external medium. In AGN the deceleration by the external medium is usually unimportant and most of the initial magnetic energy is naturally converted into kinetic energy, leading to efficient dissipation in internal shocks as the sub-shells collide. Such efficient low-magnetization internal shocks can also naturally occur in GRBs, where the deceleration by the external medium can be important. A strong low-magnetization reverse shock can develop, and the initial division into sub-shells allows it to be relativistic and its emission to peak on the timescale of the prompt GRB duration (which is not possible for a single shell). Sub-shells also enable the outflow to reach much higher Lorentz factors that help satisfy existing constraints on GRBs from intrinsic pair opacity and from the afterglow onset time.

22 pages, 2 figures, accepted to MNRAS (the abstract and introduction are now easier to follow)

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• GRBs from Magnetic Reconnection: Variability and Robustness of Lightcurves
• GRB Spectrum from Gradual Dissipation in a Magnetized Outflow
• 2D Relativistic MHD Simulations of the Kruskal-Schwarzschild Instability in a Relativistic Striped Wind
• Supersonic turbulence in 3D isothermal flow collision
• Ambient magnetic field amplification in shock fronts of relativistic jets: an application to GRB afterglows
• Constraining Magnetization of Gamma-Ray Bursts Outflows using Prompt Emission Fluence
• Internal shocks in microquasar jets with a continuous Lorentz factor modulation
• Shock corrugation to the rescue of the internal shock model in microquasars: The single-scale MHD view