X-Ray and Gamma-Ray Emissions from the PSR 1259$-$63/Be Star System

Abstract

Abstract PSR1259$-$63 is a radio pulsar orbiting a Be star in a highly eccentric orbit. Soft and hard X-rays are observed from this binary system. We applied a shock-powered emission model to this system. The collision of the pulsar and Be star winds forms a shock, which accelerates electrons and positrons to relativistic energies. We derived the energy distribution of relativistic electrons and positrons as a function of the distance from the shock in the pulsar nebula. We calculated the X-rays and $\gamma$-rays emitted from the relativistic electrons and positrons in the nebula at various orbital phases, while fully taking into account the Klein–Nishina effect. The shock-powered emission model can explain the observed X-ray properties approximately. We obtained from comparisons with observations that a fraction of $\sim 0.1$ of the pulsar spin-down luminosity should be transformed into the relativistic electrons and positrons. We found that the magnetization parameter of the pulsar wind, the ratio of the Poynting flux to the kinetic energy flux, is $\sim 0.1$ immediately upstream of the termination shock of the pulsar wind, and may decrease with the distance from the pulsar. We predict a flux of 10 MeV–100 GeV $\gamma$–rays, which may be nearly equal to the detection threshold in the future projects.