TY - GEN
T1 - Force-free simulations of ultra-relativistic jets
AU - Tchekhovskoy, Alexander
AU - McKinney, Jonathan C.
AU - Narayan, Ramesh
PY - 2008
Y1 - 2008
N2 - We describe time-dependent axisymmetric numerical simulations of ultrarelativistic highly-magnetized, force-free jets. The simulations follow the jet from the central engine to beyond six orders of magnitude in radius. The simulated jets are confined by an external pressure which we take to vary as a power-law with distance along the jet. We find that the radial distance over which the jet is pressure supported determines the terminal Lorentz factor. For the collapsar model of GRBs, this distance is set by the size of the progenitor star and is very large. At this distance our fiducial model generates a Lorentz factor γ∼400 and a half-opening angle θj∼2°, consistent with observations of many long GRBs. Other models with slightly different parameters give γ in the range 100 to 5000 and θj from 0.1° to 10°, thus reproducing the range of properties inferred for GRB jets. A potentially observable feature of some of our solutions is that both γ and the Poynting flux S are concentrated in hollow cones, with the half-opening angle of the γ-cone θγ≪θj and the half-opening angle of the S-cone θs=θj. In the case of systems such as AGN, XRBs, and short GRBs, we expect the confining medium, viz., the disk wind, to act over a shorter range of distance. This would explain the lower terminal Lorentz factor of these systems compared to long GRBs.
AB - We describe time-dependent axisymmetric numerical simulations of ultrarelativistic highly-magnetized, force-free jets. The simulations follow the jet from the central engine to beyond six orders of magnitude in radius. The simulated jets are confined by an external pressure which we take to vary as a power-law with distance along the jet. We find that the radial distance over which the jet is pressure supported determines the terminal Lorentz factor. For the collapsar model of GRBs, this distance is set by the size of the progenitor star and is very large. At this distance our fiducial model generates a Lorentz factor γ∼400 and a half-opening angle θj∼2°, consistent with observations of many long GRBs. Other models with slightly different parameters give γ in the range 100 to 5000 and θj from 0.1° to 10°, thus reproducing the range of properties inferred for GRB jets. A potentially observable feature of some of our solutions is that both γ and the Poynting flux S are concentrated in hollow cones, with the half-opening angle of the γ-cone θγ≪θj and the half-opening angle of the S-cone θs=θj. In the case of systems such as AGN, XRBs, and short GRBs, we expect the confining medium, viz., the disk wind, to act over a shorter range of distance. This would explain the lower terminal Lorentz factor of these systems compared to long GRBs.
KW - Astrophysical jets
KW - Black holes
KW - Gamma-ray bursts
KW - Plasma magnetohydrodynamics
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U2 - 10.1063/1.3002510
DO - 10.1063/1.3002510
M3 - Conference contribution
AN - SCOPUS:55549105460
SN - 9780735405844
T3 - AIP Conference Proceedings
SP - 71
EP - 77
BT - Cool Discs, Hot Flows
T2 - Cool Discs, Hot Flows: The Varying Faces of Accreting Compact Objects
Y2 - 25 March 2008 through 30 March 2008
ER -