2013MNRAS.431.2645T

We discuss a possible scenario for radiation mechanism of pulsed GeV γ-rays from magnetars. The magnetars have shown frequent X-ray bursts, which would be triggered by crust fractures and could release the energy of order of Etot ∼ 1041-42erg. If the location of the crust cracking of the magnetic field is close to the magnetic pole, part of the released energy may excite the Alfven wave that can propagate into outer magnetosphere. The oscillation of the magnetic field induces the available potential drop δΦp ∼ 1015 V, which can accelerate the electrons and/or positrons to the Lorentz factor Γ ∼ 107 in the outer magnetosphere. The curvature radiation process at outer magnetosphere can produce GeV γ-rays. If the radiation process is occurred above r ∼ 5x107 cm from the stellar surface, the emitted GeV γ-rays can escape from the pair-creation process with the X-rays and/or the magnetic field. The expected luminosity of the GeV emissions is order of Lγ ≤ 1035ergs-1, and the radiation process will last for a temporal scale of years. The expected pulse profiles have a broad shape with sometimes sharp peaks. We apply the model to anomalous X-ray pulsar 1E 2259+586.