Highly magnetized region in pulsar wind nebulae and origin of the Crab gamma-ray flares

摘要

The recently discovered gamma-ray flares from the Crab nebula are generallyattributed to the magnetic energy release in a highly magnetized region withinthe nebula. I argue that such a region naturally arises in the polar region ofthe inner nebula. In pulsar winds, efficient dissipation of the Poynting fluxinto the plasma energy occur only in the equatorial belt where the energy ispredominantly transferred by alternating fields. At high latitudes, the pulsarwind remains highly magnetized therefore the termination shock in the polarregion is weak and the postshock flow remains relativistic. I study thestructure of this flow and show that the flow at first expands and deceleratesand then it converges and accelerates. In the converging part of the flow, thekink instability triggers the magnetic dissipation. The energy release zoneoccurs at the base of the observed jet. A specific turbulence ofrelativistically shrinking magnetic loops efficiently accelerates particles sothat the synchrotron emission in the hundreds MeV band, both persistent andflaring, comes from this site.