High-energy gamma-ray emission from anomalous X-ray pulsars

We study the high-energy gamma-ray radiation from the outer magnetospheres of the anomalous X-ray pulsars. For pulsars with superstrong magnetic fields (B > 10(14) G), the magnetic field in the region far away from the neutron star surface drops below the quantum critical value, and high-energy gamma-ray emission can be emitted. The electrons/positrons produced by collisions between high-energy photons from the outer gap and the soft X-rays resulting from the stellar surface are accelerated inside the outer gap and emit the high-energy gamma rays through curvature radiation. The gamma-ray spectrum and luminosity in this model can be estimated once the pulsar parameters such as period, surface magnetic field, and surface temperature are given. We apply this model to some anomalous X-ray pulsars such as 4U 0142+615, 1E 1048.1-5937, RX J170849-4009, 1E 1841-045, and 1E 2259-586 and suggest that their gamma-ray fluxes could be detected by the Gamma-Ray Large-Area Space Telescope.