Abstract
Among the brightest sources of X-ray emission are supernova remnants (SNRs), which will be extensively observed by new X-ray satellites (Chandra, XMM, and Astro-E). Thermal X-ray emission from SNRs cannot be analyzed with standard X-ray plasma codes, because plasmas in these objects are not in ionization equilibrium. Nonequilibrium ionization (NEI) models are necessary in order to take advantage of the anticipated flood of high quality X-ray data on SNRs. I present a basic set of NEI models for analysis of thermal X-ray spectra of SNRs: constant-temperature, single ionization timescale models, generalized single ionization timescale models, plane-parallel shocks with constant electron temperature, plane-parallel shocks and Sedov models with unequal ion and electron temperatures.