We show that the mysterious, rapidly variable emission at ~400 MeV observedfrom the Crab Nebula by the AGILE and Fermi experiments could be the result ofa sudden drop in the mass-loading of the pulsar wind. The current required tomaintain wave activity in the wind is then carried by very few particles ofhigh Lorentz factor. On impacting the Nebula, these particles produce a tightlybeamed, high luminosity burst of hard gamma-rays, similar to those observed.This implies (i) the emission is synchrotron radiation in the toroidal field ofthe Nebula, and, therefore, linearly polarized and (ii) this mechanismpotentially contributes to the gamma-ray emission from other powerful pulsars,such as the Magellanic Cloud objects J0537-6910 and B0540-69.
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