Magnetic acceleration of ultrarelativistic jets in gamma-ray burst sources

By Serguei Komissarov, Nektarios Vlahakis, A. Königl, M. Barkov. 2008

286 citations recorded by the source corpus.

We present numerical simulations of axi symmetric, magnetically driven outflows that reproduce the inferred properties of ultrarelativistic gamma-ray burst (GRB) jets. These results extend our previous simulations of outflows accelerated to moderately relativistic speeds, which are applicable to jets of active galactic nuclei. In contrast to several recent investigations, which have employed the magnetodynamics approximation, our numerical scheme solves the full set of equations of special relativistic, ideal magnetohydrodynamics, which enables us to explicitly calculate the jet velocity and magnetic-to-kinetic energy conversion efficiency - key parameters of interest for astrophysical applications. We confirm that the magnetic acceleration scheme remains robust into the ultrarelativistic regime, as previously indicated by semi-analytic self-similar solutions. We find that all current-carrying outflows exhibit self-collimation and consequent acceleration near the rotation axis, but that unconfined outflows lose causal connectivity across the jet and therefore do not collimate or accelerate efficiently in their outer regions. We show that magnetically accelerated jets confined by an external pressure that varies as z -α (0 1), and we obtain analytic expressions for the one-to-one correspondence between the pressure distribution and the asymptotic jet shape. We demonstrate that the acceleration efficiency of jets with paraboloidal streamlines is ≥50 per cent, with the numerical value being higher the lower the initial magnetization. We derive asymptotic analytic expressions for the acceleration of initially cold outflows along paraboloidal streamlines and verify that they provide good descriptions of the simulated flows. Our modelled jets (corresponding to 3/2 < a < 3) attain Lorentz factors Γ ≥ 10 2 on scales ∼ 10 10 -10 12 cm, consistent with the possibility that long/soft GRB jets are accelerated within envelopes of collapsing massive stars, and r ≥ 30 on scales ∼9 x 10 8 -3 x 10 10 cm, consistent with the possibility that short/hard GRB jets are accelerated on scales where they can be confined by moderately relativistic winds from accretion discs. We also find that Γθ v ∼ 1 for outflows that undergo an efficient magnetic-to-kinetic energy conversion, where θ v is the opening half-angle of the poloidal streamlines. This relation implies that the γ-ray emitting components of GRB outflows accelerated in this way are very narrow, with θ v ≤ 1° in regions where Γ ≥ 100, and that the afterglow light curves of these components would either exhibit a very early jet break or show no jet break at all.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/0aa1d27cf0bafff3d05658322f121ea412cd4997

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Citations in the corpus

Gamma-ray bursts in the comoving frame (2011, background): “Some numerical simulations (Komissarov et al., 2009) of jet acceleration have shown that a magnetic dominated jet confined by an external medium should haveθjΓ06 1.”
THE INTERNAL-COLLISION-INDUCED MAGNETIC RECONNECTION AND TURBULENCE (ICMART) MODEL OF GAMMA-RAY BURSTS (2010, background): “Second, the Poynting flux may be directly converted to kinetic energy without dissipation (e.g. Vlahakis and Königl 2003; Komissarov et al. 2009) under the pressure gradient of magnetic fields in an MHD flow.”
A Reconnection Switch to Trigger gamma-Ray Burst Jet Dissipation (2010, background): “…2006, 2007), only recently have self-consistent MHD simulations been able to model the formation and large-scale axisymmetric structure of such jets (Komissarov et al. 2009; Lyubarsky 2010a), including what happens beyond a stellar envelope in the collapsar model (Tchekhovskoy, Narayan & McKinney…”
The birth of black holes: neutron star collapse times, gamma-ray bursts and fast radio bursts (2014, background): “Jet launching through magnetic acceleration requires a short-lived (∼0.1–1 s) accretion disc, and toroidal and small-opening-angle poloidal magnetic fields that are both ∼1015 G (e.g. Komissarov et al. 2009).”
Three-dimensional magnetohydrodynamic simulations of the Crab nebula (2013, background): “Although claims have been made that ideal MHD acceleration mechanisms can provide the required energy conversion (e.g. Vlahakis 2004), it has now become clear that this is not the case (e.g. Komissarov et al. 2009; Lyubarsky 2009, 2010).”
ASYMPTOTIC STRUCTURE OF POYNTING-DOMINATED JETS (2009, methodology): “Both an analytical solution for the paraboloidal flux surfaces (Blandford 1976; Beskin & Nokhrina 2006) and numerical simulations (Komissarov et al. 2007, 2009; Tchekhovskoy et al. 2008) show that this is a good approximation for such jets.”
The physics of gamma-ray bursts & relativistic jets (2014, background): “If the pressure of the ambient medium decreases as p ∝ R−a, then the transverse size of the jet and the jet Lorentz factor both increase as Ra/4 for a ≤ 2 (Komissarov et al., 2009) 50 .”
EFFICIENCY OF MAGNETIC TO KINETIC ENERGY CONVERSION IN A MONOPOLE MAGNETOSPHERE (2009, background): “We remark that while preparing this paper for publication, Komissarov et al. (2009) posted a paper describing ideal MHD simulations of confined and unconfined winds.”
Relativistic Jets Shine through Shocks or Magnetic Reconnection (2015, background): “…flow to relativistic speeds but, generally, magnetohydrodynamic (MHD) models predict that the largest fraction of the energy remains locked in the magnetic field, i.e., the jet arrives Poynting-dominated atthe dissipation distance (Tchekhovskoy et al. 2009; Komissarov et al. 2009; Lyubarsky 2009).”
The Proto-Magnetar Model for Gamma-Ray Bursts (2010, background): “Analytic (e.g. Vlahakis & Königl 2001; Narayan et al. 2007) and numerical (Komissarov et al. 2007, 2009; Tchekhovskoy et al. 2009, 2010) calculations show that if the jet is confined into a parabolic shape, additional acceleration is possible due to ‘equilibrium collimation’.”
EARLY X-RAY AND OPTICAL AFTERGLOW OF GRAVITATIONAL WAVE BURSTS FROM MERGERS OF BINARY NEUTRON STARS (2012, unknown): “A magnetized flow can be quickly accelerated to Γ ∼ σ 1/3 0 ∼ 10 3 at R0 ∼ 10 7 cm, where σ ∼ σ 2/3 0 ∼ 10 6 (Komissarov et al. 2009).”
THE MISSING LINK: MERGING NEUTRON STARS NATURALLY PRODUCE JET-LIKE STRUCTURES AND CAN POWER SHORT GAMMA-RAY BURSTS (2011, methodology): “This regime, which was not accessible to previous simulations (Price & Rosswog 2006; Anderson et al. 2008; Liu et al. 2008), is essential for the jet formation (Aloy et al. 2005; Komissarov et al. 2009).”
THE STRUCTURE OF THE M87 JET: A TRANSITION FROM PARABOLIC TO CONICAL STREAMLINES (2011, background): “For a general (non-self-similar) case,b > 2 is allowed in 1 The original value is replaced by taking into account of the mass difference of SMBH. analytical and numerical models (Tchekhovskoy et al. 2008; Lyubarsky 2009; Komissarov et al. 2009).”
BLACK HOLE SPIN AND THE RADIO LOUD/QUIET DICHOTOMY OF ACTIVE GALACTIC NUCLEI (2009, background): “The ratio of magnetic to kinetic energy flux at the base of the jet determines the asymptotic Lorentz factor (Begelman & Li 1994; Komissarov et al. 2009; Tchekhovskoy et al. 2009a, 2009b).”