Focusing of Alfvénic power in neutron star magnetospheres

Abstract

Highly dynamic magnetospheric perturbations in neutron star environments can naturally account for the features observed in gamma‐ray burst spectra. However, if GRB’s have an extragalactic origin, as is implied by the uniform yet spatially truncated distribution observed by the BATSE experiment, then noncatastrophic isotropic emission mechanisms may be ruled out on energetic and timing arguments. As such, we consider MHD processes which can produce strongly anisotropic γ‐rays with an observable flux out to distances of ∼1–2 Gpc. In particular, 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 charges generating the current which sustains the field misalignment, and thereby focus their power into a spatial region (i.e., the shear) that can be many times smaller than that of the crustal disturbance. This produces a strong (observable) flux enhancement along certain directions. © 1994 American Institute of Physics.