Multi-wavelength pulse profiles from the force-free neutron star magnetosphere

Abstract

In this paper, we compute a full atlas of radio, X-ray and $\gamma$-ray pulse profiles relying on the force-free magnetosphere model. Our goal is to use such data bank of multi-wavelength profiles to fit a substantial number of radio-loud $\gamma$-ray pulsars also detected in non-thermal X-rays to decipher the X-ray radiation mechanism and sites. Using results from the third $\gamma$-ray pulsar catalogue (3PC), we investigate the statistical properties of this population. We assume that radio emission emanates from field lines rooted to the polar caps, at varying height above the surface, close to the surface, at an altitude about 5-10% of the light-cylinder radius $r_{\rm L}$. The X-ray photons are produced in the separatrix region within the magnetosphere, i.e. the current sheet formed by the jump from closed to open magnetic field lines. We allow for substantial variations in emission height. The $\gamma$-ray are produced within the current sheet of the striped wind, outside the light-cylinder. A comprehensive set of light-curves in radio, X-ray and $\gamma$-ray has been computed. Based on only geometric considerations about magnetic obliquity, line of sight inclination and radio beam cone opening angle, pulsars can be classified as radio-loud or quiet and $\gamma$-ray loud or quiet. We found that the 3PC sample is compatible with an isotropic distribution of obliquity and line of sight. The atlases constructed in this work are the fundamental tools to explore individual pulsars and fit their multi-wavelength pulse profiles in order to constrain their magnetic topology, the emission sites as well as the observer line of sight.