EFFICIENCY OF MAGNETIC TO KINETIC ENERGY CONVERSION IN A MONOPOLE MAGNETOSPHERE

By A. Tchekhovskoy, J. McKinney, Ramesh Narayan. 2009

141 citations recorded by the source corpus.

Unconfined relativistic outflows from rotating, magnetized compact objects are often well modeled by assuming that the field geometry is approximately a split-monopole at large radii. Earlier work has indicated that such an unconfined flow has an inefficient conversion of magnetic energy to kinetic energy. This has led to the conclusion that ideal magnetohydrodynamical (MHD) processes fail to explain observations of, e.g., the Crab pulsar wind at large radii where energy conversion appears efficient. In addition, as a model for astrophysical jets, the monopole field geometry has been abandoned in favor of externally confined jets since the latter appeared to be generically more efficient jet accelerators. We perform time-dependent axisymmetric relativistic MHD simulations in order to find steady-state solutions for a wind from a compact object endowed with a monopole field geometry. Our simulations follow the outflow for 10 orders of magnitude in distance from the compact object, which is large enough to study both the initial “acceleration zone” of the magnetized wind as well as the asymptotic “coasting zone.” We obtain the surprising result that acceleration is actually efficient in the polar region, which develops a jet despite not being confined by an external medium. Our models contain jets that have sufficient energy to account for moderately energetic long and short gamma-ray burst (GRB) events (∼1051–1052 erg), collimate into narrow opening angles (opening half-angle θj ≈ 0.03 rad), become matter-dominated at large radii (electromagnetic energy flux per unit matter energy flux σ < 1), and move at ultrarelativistic Lorentz factors (γj ∼ 200 for our fiducial model). The simulated jets have γjθj ∼ 5–15, so they are in principle capable of generating “achromatic jet breaks” in GRB afterglow light curves. By defining a “causality surface” beyond which the jet cannot communicate with a generalized “magnetic nozzle” near the axis of rotation, we obtain approximate analytical solutions for the Lorentz factor that fit the numerical solutions well. This allows us to extend our results to monopole wind models with arbitrary magnetization. Overall, our results demonstrate that the production of ultrarelativistic jets is a more robust process than previously thought.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/dd0803820307687cdd6168c9f6474b7fae1a623d

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Citations in the corpus

General relativistic magnetohydrodynamic simulations of magnetically choked accretion flows around black holes (2012, background): “…flux comes from large radii, as implicit in outflow models (Blandford 1976; Blandford & Znajek 1977; Blandford & Payne 1982; Narayan et al. 2007; Tchekhovskoy et al. 2009, 2010a,b), but transport of flux from large radii may be inefficient (Lubow et al. 1994; Spruit & Uzdensky 2005; Rothstein &…”
BLACK HOLE SPIN AND THE RADIO LOUD/QUIET DICHOTOMY OF ACTIVE GALACTIC NUCLEI (2009, methodology): “At the wall, we outflow (copy) the components of velocity and magnetic field that are parallel to the wall, and mirror the perpendicular components (Tchekhovskoy et al. 2009a).”
A Reconnection Switch to Trigger gamma-Ray Burst Jet Dissipation (2010, methodology): “…generalized axisymmetric steady-state jet solution is presented as based upon approximate analytical solutions that have been confirmed numerically (Tchekhovskoy et al. 2008, 2009, 2010b) using the HARM code (Gammie, McKinney & Tóth 2003; Noble et al. 2006; Mignone & McKinney 2007; Tchekhovskoy,…”
Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program (2017, background): “Such a connection is in fact expected in standard theories of the formation, acceleration, and collimation of relativistic jets (e.g., Blandford & Königl 1979; Tchekhovskoy et al. 2009).”
Relativistic MHD simulations of core-collapse GRB jets: 3D instabilities and magnetic dissipation (2015, methodology): “We carry out our simulations using the HARM code (Gammie et al 2003), with recent improvements (McKinney 2006; Tchekhovskoy et al. 2007, 2009; McKinney & Blandford 2009, Tchekhovskoy et al. 2011).”
AFTERGLOW OBSERVATIONS OF FERMI LARGE AREA TELESCOPE GAMMA-RAY BURSTS AND THE EMERGING CLASS OF HYPER-ENERGETIC EVENTS (2010, background): “Tchekhovskoy et al. (2009b) have recently conducted fully relativistic MHD simulations in which a mildly magnetized (magnetization parameter σ .”
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’.”
RESISTIVE SOLUTIONS FOR PULSAR MAGNETOSPHERES (2011, background): “If particles start out on the stellar surface with non-relativistic Resistive Pulsar Magnetospheres 3 velocity, then the fluid essentially satisfies this condition in the high conductivity limit (see e.g., Contopoulos & Kazanas 2002; Tchekhovskoy et al. 2009; Beskin 2010).”
Prograde and retrograde black holes: whose jet is more powerful? (2012, methodology): “We carried out time-dependent 3D general relativistic non-radiative MHD simulations using a high-order version of Godunov-type shock-capturing code HARM (Gammie et al. 2003; McKinney & Gammie 2004; Tchekhovskoy et al. 2007, 2009; McKinney & Blandford 2009) in modified spherical polar coordinates.”
The physics of gamma-ray bursts & relativistic jets (2014, background): “The hot cocoon surrounding the jet also helps in its collimation and acceleration, and magnetic jets require less expenditure of energy to punch through the star than baryonic jets of same luminosity and cross-section at the launching site [626,627, 721,722].”
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).”