Intermittent mildly magnetized jets as the source of GRBs

Abstract

Gamma-ray bursts (GRBs) are powered by relativistic jets that exhibit intermittency over a broad range of timescales - from $\sim$ ms to seconds. Previous numerical studies have shown that hydrodynamic (i.e., unmagnetized) jets that are expelled from a variable engine are subject to strong mixing of jet and cocoon material, which strongly inhibits the GRB emission. In this paper we conduct 3D RMHD simulations of mildly magnetized jets with power modulation over durations of 0.1 s and 1 s, and a steady magnetic field at injection. We find that when the jet magnetization at the launching site is $\sigma \sim 0.1$, the initial magnetization is amplified by shocks formed in the flow to the point where it strongly suppresses baryon loading. We estimate that a significant contamination can be avoided if the magnetic energy at injection constitutes at least a few percent of the jet energy. The variability timescales of the jet after it breaks out of the star are then governed by the injection cycles rather than by the mixing process, suggesting that in practice jet injection should fluctuate on timescales as short as $\sim 10$ ms in order to account for the observed light curves. Better stability is found for jets with shorter modulations. We conclude that for sufficiently hot jets, the Lorentz factor near the photosphere can be high enough to allow efficient photospheric emission. Our results imply that jets with $10^{-2}<\sigma <1$ injected by a variable engine with $\sim 10$ ms duty cycle are plausible sources of long GRBs.

References in corpus (9)

• PLUTO: a Numerical Code for Computational Astrophysics
• GRB Radiative Efficiencies Derived from the Swift Data: GRBs vs. XRFs, Long vs. Short
• 3D Relativistic Magnetohydrodynamic Simulations of Current-Driven Instability. I. Instability of a static column
• The structure of weakly-magnetized $\gamma$-ray burst jets
• High efficiency photospheric emission entailed by formation of a collimation shock in gamma-ray bursts
• Propagation, cocoon formation, and resultant destabilization of relativistic jets
• Linear Theory of the Rayleigh-Taylor Instability at a Discontinuous Surface of a Relativistic Flow
• Magnetic inhibition of the recollimation instability in relativistic jets
• Rotation and toroidal magnetic field effects on the stability of two-component jets

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