  The ~400 MeV flaring emission from the Crab Nebula is naturally explained as
the result of an abrupt reduction in the mass-loading of the pulsar wind. Very
few particles are then available to carry the current required to maintain wave
activity, causing them to achieve high Lorentz factors. When they penetrate the
Nebula, a tightly beamed, high luminosity burst of hard gamma-rays results,
with characteristics similar to the observed flares. This mechanism may operate
in other powerful pulsars, such as J0537-6910 (PWN N 157B), B0540-69, B1957+20
and J0205+6449 (3C 58).
