Magnetic acceleration of ultra-relativistic GRB and AGN jets

Abstract

We present numerical simulations of cold, axisymmetric, magnetically driven relativistic outflows. The outflows are initially sub-Alfvénic and Poynting flux-dominated, with total--to--rest-mass energy flux ratio up to $\mu \sim 620$. To study the magnetic acceleration of jets we simulate flows confined within a funnel with rigid wall of prescribed shape, which we take to be $z\propto r^a$ (in cylindrical coordinates, with $a$ ranging from 1 to 2). This allows us to eliminate the numerical dissipative effects induced by a free boundary with an ambient medium. We find that in all cases they converge to a steady state characterized by a spatially extended acceleration region. For the jet solutions the acceleration process is very efficient - on the outermost scale of the simulation more than half of the Poynting flux has been converted into kinetic energy flux, and the terminal Lorentz factor approached its maximum possible value (${\Gamma }_{\infty }\simeq \mu$). The acceleration is accompanied by the collimation of magnetic field lines in excess of that dictated by the funnel shape. The numerical solutions are generally consistent with the semi-analytic self-similar jets solutions and the spatially extended acceleration observed in some astrophysical relativistic jets. In agreement with previous studies we also find that the acceleration is significantly less effective for wind solutions suggesting that pulsar winds may remain Poynting dominated when they reach the termination shock.

arXiv comment4 pages, 3 figures, HEPRO-2007 Dublin

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• Gamma-ray flares from red giant/jet interactions in AGN
• Magnetohydrodynamic models of astrophysical jets
• Interpretation of the flares of M87 at TeV energies in the cloud-jet interaction scenario
• Star-Jet Interactions and Gamma-Ray Outbursts from 3C454.3
• Radio precursors to neutron star binary mergings
• Accretion of a massive magnetized torus on a rotating black hole
• On the central core in MHD winds and jets
• The Evolution of Gamma-ray Burst Jet Opening Angle through Cosmic Time
• From young to old: the evolutionary path of Pulsar Wind Nebulae
• Radio Loud vs. Radio Quiet Gamma-ray Bursts: the Role of Binary Progenitors
• A MAD Explanation for the Correlation between Bulk Lorentz Factor and Minimum Variability Timescale