Introduction

We are discussing the state of the art of X-ray polarization detection techniques in this conference, so that it is important to remind ourselves of the expected X-ray polarization properties of various astrophysical objects. In this paper, we give a brief overview of the expected X-ray polarization signatures of magnetic neutron stars found in diverse situations, e.g. in accretion-powered pulsars, low-mass X-ray binaries (LMXBs), recycled pulsars, isolated neutron stars and finally the fascinating magnetars. We concentrate here only on some aspects of the basic physics of radiation propagation around magnetized neutron stars which lead to some basic, expected polarization features in the X-rays which we consider relatively robust. Accordingly, our discussion here is qualitative. Quantitative aspects of a few of these features have been described by other participants of the conference, and detailed calculations on some other aspects will be reported elsewhere.

The X-ray emission we are concerned with here is basically thermal emission from the surface of the neutron star, powered by accretion or otherwise. This radiation propagates through the neutron-star atmosphere, then through the accretion columns over the magnetic poles of the neutron star if it is an accreting one, and finally through the neutron-star magnetosphere.