On the Study of NEI Regime in SNR's: Emission Model and ROSAT PSPC Spectral Fitting Simulations

We developed and tested a Non-Equilibrium of Ionization (NEI) emission model to study the X-ray emission of supernova remnants (SNR's) with a paramet-ric tting approach. We present results of ROSAT PSPC spectral tting simulations with our emission model. We found that, the conndence ranges of the plasma temperature tend to be larger with respect to ts with equilibrium of ionization models, the 2 function is characterized by local minima in the parameter space, and there is a strong dependence of the t results on the initial value of the ionization time used in the minimization algorithm. We explain these ndings in terms of the particular nature of the model. We conclude that, in typical cases of young and middle-aged SNR with a moderate ISM absorption, the local minima can be avoided by the 2 tting spectra with 5000 counts or more. Finally, we brieey discuss how this limit aaects the feasibility of spatially resolved spectral analysis of SNR's observed with the PSPC.