Some effects of nonlinear vacuum electrodynamics in strong magnetic and   gravitational fields of the pulsar
  We consider the propagation of X-ray and gamma ray emissions in strong magnetic and gravitational fields of the pulsar in nonlinear vacuum electrodynamics. We show that the radiation will spread from the pulsar to the detecting device in the form of two normal modes polarized in mutually orthogonal planes, and having different velocities. We have calculated the delay between the two modes, as they propagate from the pulsar to the detecting device. 
Medeu Abishev, Yerlan Aimuratov, Yermek Aldabergenov, Nurzada Beissen   and Meruert Takibayeva
gr-qc