1996A&AS..120C.111H

Magnetic photon splitting is an exotic QED process which becomes important in fields approaching the quantum critical value of 4.41x10¹³Gauss. Its principal effect is to degrade photon energies below the threshold for magnetic single photon pair production. In this paper, we consider the importance of photon splitting in γ-ray pulsars, specifically focusing on PSR 1509-58, because of its large spin-down field (B=3x10¹³Gauss). We present calculations of the splitting attenuation length, including the influence of the dipole field and curved spacetime geometry of a neutron star magnetosphere. Test photons originate at different locations on the neutron star surface, initially propagating parallel to the field lines. It is found that splitting prevents γ-rays emitted from a polar cap of 5°-10° from escaping the magnetosphere when their energy exceeds about 30-50MeV in fields ∼10¹³Gauss. Comparison with attenuation lengths for pair creation indicates that splitting is more important in polar cap models for PSR 1509-58 in the 10-200MeV range: splitting suppresses the creation of pairs and inhibits escape of any near-surface emission above about 10-20MeV, depending on polar cap size. General relativistic effects on photon trajectories and on the magnetic field decrease the escape energies significantly.