Non-thermal origin of X-rays from rotation-powered neutron stars

The X-ray emission from 27 rotation powered pulsars have been detected so far by ROSAT and ASCA. The observed emission properties in the soft X-ray band have been recently reviewed by Becker & Trumper (1997). The most remarkable effect reported in this review is an apparently linear relationship between the X-ray luminosity Lx for all rotation-powered pulsars detected by ROSAT and the spin-down luminosity Lsd A very narrow distribution of Lx around 10(-3) L-sd extends over eight orders of magnitude. In this paper we propose a model which explains the linear relationship L-x approximate to 10(-3) L-sd by means of magnetospheric synchrotron radiation of secondary ei pairs produced by high energy curvature photons in the strong pulsar magnetic field near the neutron star surface.