Physical properties of amorphous solid interstellar material from X-ray absorption spectroscopy of Sco X-1

Abstract

High quality, high resolution X-ray spectra were obtained of Sco X-1 with the Reflection Grating Spectrometer (RGS) on board the XMM-Newton satellite. The spectrum around the Oxygen K-edge is searched for signatures indicative for EXAFS. Analysis shows a clear indication for the existence of EXAFS with photo-electron scattering distances in the absorbing medium in a range which applies to many solids. When scattering of the photo-electron on Oxygen atoms is assumed, the Oxygen to Oxygen atom distances found are 2.75 Angstrom. This fits with distances as found in amorphous water-ice, although water ice is thought to be an unlikely constituent of the diffuse interstellar clouds which form the absorbing medium towards Sco X-1