Emission measures and emission-measure-weighted temperatures of shocked interstellar medium and ejecta in supernova remnants

A goal of supernova remnant (SNR) evolution models is to relate fundamental parameters of a supernova (SN) explosion and progenitor star to the current state of its SNR. The SNR hot plasma is characterized by its observed X-ray spectrum, which yields electron temperature, emission measure (EM), and abundances. Depending on their brightness, the properties of the plasmas heated by the SNR forward shock, reverse shock, or both can be measured. The current work uses models that are spherically symmetric. One-dimensional hydrodynamic simulations are carried out for SNR evolution prior to onset of radiative losses. From these, we derive dimensionless EMs and EM-weighted temperatures, and we present fitting formulae for these quantities as functions of scaled SNR time. These models allow one to infer SNR explosion energy, circumstellar medium density, age, ejecta mass, and ejecta density profile from SNR observations. The new results are incorporated into the SNR modeling code SNRPy. The code is demonstrated with application to three historical SNRs: Kepler, Tycho, and SN1006.