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Session 44 - New Light on Supernova Remnants.
Display session, Wednesday, June 11
South Main Hall,
We describe results from an updated X-ray nonequilibrium-ionization code using as a dynamical substrate a Sedov-Taylor blast wave appropriate for a supernova remnant. The code has extensively updated atomic physics, particularly in Fe L-shell transitions, and allows for an arbitrary ratio \beta of the postshock electron temperature T_e to the mean temperature T, to describe possible nonthermal plasma heating processes in the shock wave. Previous results indicate that simple models, such as constant-temperature nonequilibrium-ionization models, do not adequately approximate these full calculations. We present new findings concerning the ability of XSPEC to distinguish among our calculated, Sedov-based models using the response function of the ASCA satellite. In all cases, the ionization timescale of the remnant is well determined. Models with high postshock electron temperatures (T_e = 3.5 keV) can be recognized, but only the product of the mean temperature T and \beta can be found as models with equal \beta T are indistinguishable. However, at lower temperatures (T_e = 0.35 keV), XSPEC can differentiate among models having equal values of \beta T. The value of \beta can be constrained and T is found to within 5%. Proper spectral binning is essential to these results because of the influence of \beta on the high-energy portion of the spectrum where photon counts are low. We also investigate the observed flux level required to make such distinctions at ASCA resolution and sensitivity. Due to the complexity of the Sedov-Taylor substrate, the models cannot be generated for real-time fitting. We have generated a substantial grid of models, which map a three-dimensional parameter space in postshock temperature, ionization parameter, and \beta. We plan to make these XSPEC-ready models available to the general astronomical community.
Program listing for Wednesday