code: def coreBurkAlpha(self, R, Rs, rho0, r_core, ax_x, ax_y):
          
          x = R * Rs ** -1
          p = Rs * r_core ** -1
  
          gx = self._G(x, p)
  
          a = 2 * rho0 * Rs ** 2 * gx / x
  
          return a * ax_x / R, a * ax_y / R
docs: deflection angle
  
          :param R:
          :param Rs:
          :param rho0:
          :param r_core:
          :param ax_x:
          :param ax_y:
          :return: