The recently discovered gamma-ray flares from the Crab nebula are generally
attributed to the magnetic energy release in a highly magnetized region within
the nebula. I argue that such a region naturally arises in the polar region of
the inner nebula. In pulsar winds, efficient dissipation of the Poynting flux
into the plasma energy occur only in the equatorial belt where the energy is
predominantly transferred by alternating fields. At high latitudes, the pulsar
wind remains highly magnetized therefore the termination shock in the polar
region is weak and the postshock flow remains relativistic. I study the
structure of this flow and show that the flow at first expands and decelerates
and then it converges and accelerates. In the converging part of the flow, the
kink instability triggers the magnetic dissipation. The energy release zone
occurs at the base of the observed jet. A specific turbulence of
relativistically shrinking magnetic loops efficiently accelerates particles so
that the synchrotron emission in the hundreds MeV band, both persistent and
flaring, comes from this site.Comment: Submitted to MNRA