ISMabs: a comprehensive X-ray absorption model for the interstellar medium

TL;DR

ISMabs is an advanced X-ray absorption model for the interstellar medium that incorporates both neutral and ionized species, utilizing accurate atomic data to improve spectral fits and enable direct ionization state measurements.

Contribution

The paper introduces ISMabs, a comprehensive X-ray absorption model that includes ionized species and is compatible with standard spectral fitting tools, enhancing analysis of interstellar medium properties.

Findings

Inclusion of ions improves spectral fit quality.

Column densities provide direct ionization state estimates.

Model is compatible with XSPEC, ISIS, and SHERPA.

Abstract

We present an X-ray absorption model for the interstellar medium, to be referred to as ISMabs, that takes into account both neutral and ionized species of cosmically abundant elements, and includes the most accurate atomic data available. Using high-resolution spectra from eight X-ray binaries obtained with the Chandra High Energy Transmission Grating Spectrometer, we proceed to benchmark the atomic data in the model particularly in the neon K-edge region. Compared with previous photoabsorption models, which solely rely on neutral species, the inclusion of ions leads to improved spectral fits. Fit parameters comprise the column densities of abundant contributors that allow direct estimates of the ionization states. ISMabs is provided in the appropriate format to be implemented in widely used X-ray spectral fitting packages such as XSPEC, ISIS and SHERPA.