Interstellar Absorption and Dust Scattering

The study of the interstellar medium (ISM) in the X-rays has entered a golden age with the advent of the X-ray observatories XMM-Newton and Chandra. High-energy resolution allowed to study dust spectroscopic features with unprecedented detail. At the same time, the X-ray imaging capabilities offered a new perspective of dust scattering halos. Both spectroscopy and imaging rely on a simple geometry, where a distant X-ray source, usually a bright X-ray binary system, lies behind a multilayered ISM. X-ray binaries can be found in different regions in the Galaxy, providing the unique chance to study the ISM in distinct environments. In the following, we will describe how X-rays can be used as a tool to study gas and dust along the line of sight, revealing elemental abundances and depletion. The study of interstellar dust spectroscopic and imaging features can be used to extract the chemical and physical properties of the intervening dust, as well as its distribution along the line of sight.