Focusing of alfvénic wave power in the context of gamma-ray burst emissivity

Highly dynamic magnetospheric perturbations in neutron star environments can naturally account for the features observed in gamma-ray burst spectra. The source distribution, however, appears to be extragalactic. Although noncatastrophic isotropic emission mechanisms may be ruled out on energetic and timing arguments, MHD processes can produce strongly anisotropic γ-rays with an observable flux out to distances of ∼1-2 Gpc. Here we show that sheared Alfvén waves propagating along open magnetospheric field lines at the poles of magnetized neutron stars transfer their energy dissipationally to the current sustaining the field misalignment and thereby focus their power into a spatial region ∼1000 times smaller than that of the crustal disturbance. This produces a strong (observable) flux enhancement along certain directions. We apply this model to a source population of "turned-off" pulsars that have nonetheless retained their strong magnetic fields and have achieved alignment at a period of ≳5 seconds.