Silicon X-ray absorption in the Galactic ISM: the gaseous component

TL;DR

This study analyzes the silicon K-edge absorption in the Galactic interstellar medium using high-resolution X-ray spectra, providing detailed ionic column densities and emphasizing the importance of accurate gaseous modeling.

Contribution

Introduces a modified ISMabs model with new Si ionic cross sections to accurately characterize the gaseous silicon in the Galactic ISM.

Findings

Similar ionic fractions for Si I and Si II suggest common physical conditions.

Estimates of Si ionic column densities across different ISM phases.

Highlights the necessity of precise gaseous modeling for ISM studies.

Abstract

We present a detailed analysis of the gaseous component of the Si K edge using high-resolution Chandra spectra of low-mass X-ray binaries. We fit the spectra with amodified version of the ISMabs model, including new photoabsorption cross sectionscomputed for all Si ionic species. We estimate column densities for Si i, Si ii, Si iii, Si xii and Si xiii, which trace the warm, intermediate temperature and hot phases of the Galactic interstellar medium. We find that the ionic fractions of the first two phases are similar. This may be due to the physical state of the plasma determined by the temperature or to the presence of absorber material in the close vicinity of the sources. Our findings highlight the need for accurate modeling of the gaseous component before attempting to address the solid component.