Radiation reflection from star surface reveals the mystery of interpulse shift and appearance of high frequency components in the Crab pulsar

Abstract

Abstract.A new mechanism of radiation emission in the polar gap of a pulsar is discussed. It is based on the curvature radiation which is emitted by positrons moving towards the surface of neutron star along field lines of the inclined magnetic field and reflects from the surface. This mechanism explains the mystery of the interpulse shift and appearance of additional components in the emission of Crab pulsar at high frequencies discovered by Moffett and Hankins twenty years ago. We discuss coherence, energy flux and spectrum of the reflected radiation, appearance and disappearance of the interpulse position shift with the frequency increase. It is also possible that a nonlinear reflection (stimulated scattering) from the star surface is observed in the form of HF components. The frequency drift of these components, discovered by Hankins, Jones and Eilek, is discussed. The nonlinear reflection is associated with "Wood's anomaly" at the diffracted waves grazing along the star surface. Two components can arise due to slow and fast waves which are present in the magnetospheric plasma. The possible scheme of their appearance due to birefringence at the reflection is also proposed. IntroductionTwenty years later after the discovery of interpulse shift and detection of the high frequency (HF) components in the radiation of the Crab pulsar by D Moffet and T Hankins [1], T Hankins, G Jones and J Eilek returned to observation of these phenomena at even higher frequencies [2]. As one of the results, a frequency drift of HF components has been discovered. The detailed analysis of physical results and problems is discussed in the authors' review [3]. The problems of interpulse shift and HF components appearance are marked there as unresolved.The figure (figure 1) from the paper [1] by Moffett and Hankins, 1996 shows that at around 3 GHz there appears a phase shift δ of interpulse (IP) of about 7 degrees comparing to the initial IP positon at lower frequencies. Moreover, two more distinct pulses -high-frequency components [2] -appear at the same frequencies [1,2]. In our preprint [4] (and subsequent papers [5,6]) and in the current work we propose the explanation of these phenomena applying the idea of the radiation reflection from the neutron star surface by returning positrons moving in the polar gap region toward the surface of the star in the inclined magnetic field (figure 2).Presently we consider in detail the curvature radiation (CR) reflected from the pulsar surface.