Absorption Of X-rays In The Interstellar Medium

A proper understanding of the absorption of X-rays by the intervening interstellar medium is important for the spectral modeling of X-ray sources. The XSPEC model tbabs takes improved abundances, new cross sections, and the influence of grains into account. We describe recent improvements to tbabs, especially the fine structure of the absorption edges of Fe-L, O, and Ne which allow tbabs to be used with gratings instruments such as the Chandra HETGS and LETGS and XMM-RGS, and verify the new model using Chandra observations. A beta-test version of tbabs suitable for compilation as a local model within XSPEC, ISIS, and other data analysis packages is available at http://astro.uni-tuebingen.de/ wilms/research/tbabs/