Iron K photons from weakly magnetized neutron stars in X-ray binaries

The emission of iron K photons by the continuum X-ray source and the neutron star surface is considered. It is shown that the continuum sources of X-ray binaries produce negligible amounts of iron K photons because nearly all iron atoms in the continuum source are fully stripped due to the intense X-ray fluxes. In contrast, the atmosphere of the neutron star in an X-ray binary might be an important source of iron K photons (photon energy about 6.5 keV) because it is bombarded by a large number of hard X-rays capable of photo-ejecting K-shell electrons from iron atoms. Information is discussed concerning the magnetic field strength, the gravitational potential at the neutron star surface, and the direction of the magnetic dipole axis which are obtainable from the observations of K photons of the neutron star atmosphere.