Bragg diffraction and the Iron crust of cold Neutron Stars

Abstract

If cooled-down neutron stars have a thin atomic crystalline-iron crust, they must diffract X-rays of appropriate wavelength. If the diffracted beam is to be visible from Earth, the illuminating source must be very intense and near the reflecting star. An example is a binary system composed of two neutron stars in close orbit, one of them inert, the other an X-ray pulsar (perhaps an "anomalous" X-ray pulsar or magnetar, not powered by gas absorption from the companion or surrounding space, would be the cleanest example). The observable to be searched for is a secondary peak added (quasi-) periodically to the main X-ray pulse. The distinguishing feature of this secondary peak is that it appears at wavelengths related by simple integer numbers, lambda, lambda/2, lambda/3... lambda/n because of Bragg's diffraction law.