Because conical segments of quasispherical ultrarelativistic blastwaves arecausally disconnected on angular scales larger than the blastwave inverseLorentz factor, astrophysical blastwaves can sustain initial anisotropy,imprinted by the process that drives the explosion, while they remainrelativistic. We show that initial angular energy fluctuations inultrarelativistic blastwaves imply a production of vorticity in the blastwave,and calculate the vortical energy production rate. In gamma-ray burst (GRB)afterglows, the number of vortical eddy turnovers as the shocked fluid crossesthe blastwave shell is about unity for marginally nonlinear anisotropy. Thusthe anisotropy must be nonlinear to explain the magnetic energy densityinferred in measured GRB spectra.
展开▼
