Studying the Fermi GeV light curve of Vela with the two-pole caustic model

Abstract

An observation of the Vela pulsar with the Fermi Large Area Telescope has been recently reported and the GeV light curve shows two main peaks with a phase separation of ∼ 0.43. We study the GeV light curve using the two-pole caustic model in which the peaks of the light curves of the pulsar result from caustic effects. The results show that the two-pole caustic model can reproduce the observed emission pattern of the two peaks and the bridge emission between them well, but overestimates the flux outside the two peaks. After taking account of the pair production effect on the azimuthal angle, we find that the resulting light curve is more consistent with the observation. We excluded the emissions from the field lines for which the distance from the null charge surface, where the pairs can be significantly produced, is larger than the radius of the light cylinder.