Oscillation-induced gamma-ray emission from dead pulsars: a model for the delayed GeV emission in gamma-ray bursts
A sudden release of the internal energy of a neutron star can cause the oscillation of crustal platelets, which will result in a high potential drop between the magnetic field lines. This potential drop accelerates e^+/- pairs in the magnetosphere and results in the emission of high-energy curvature radiation photons with energies of up to a few tens of GeV. We consider the radiation processes that take place in the stellar magnetosphere and compute the energy spectrum of particles escaping the magnetosphere. The oscillation amplitude decreases as the star radiates. Thus, the emission spectrum changes with time. In most of the `life' of the burst, the escaping photons have energies of up to 10-100 MeV. In the late stage of the emission, photons with energies of 1-100 GeV can escape photon-photon pair creation. The cut-off energies and the time-scales of emission in these two stages depend on the magnetic field, the rotation period and the available strain energy of the neutron star. If some gamma-ray bursts do come from the galactic neutron stars, our model provides an explanation of the spectral features observed.