The Effects of Elemental Abundances on Fitting Supernova Remnant Models to Data

Abstract

Models for supernova remnant (SNR) evolution can be used to determine the energy of the explosion, the age of the SNR, and the density of the surrounding medium by matching observations. Observed SNR properties derived from the X-ray spectrum include the electron temperature (kTe) and emission measure (EM) of the shocked gas. SNR models are based on hydrodynamic solutions for density, pressure, and velocity. The relations between these and kTe or EM depend on the three inputs of composition, ionization state, and electron-ion temperature ratio (Te/TI). The standard definitions and the XSPEC definitions for kTe and EM have important differences that are not well-known. The same definition used by observers of SNRs must be used in models for correct interpretation. Here, the effects of the three inputs on standard and on XSPEC versions of kTe and EM are investigated, with examples. The ratio of standard EM to the XSPEC value ranges widely, between ∼10−3 to ∼1, with smallest ratios for gas with low hydrogen abundance. The standard kTe differs from the XSPEC value by less than a few percent. For the illustrative example SNR J0049-7314, the ejecta component is shown to be consistent with core-collapse composition and a stellar wind environment.