X-ray spectroscopy of the supernova remnant RCW 86. A new challenge for modeling the emission from supernova remnants

We present an analysis of ASCA X-ray data of SNR RCW86. There appears to be a remarkable spectral variation over the remnant, indicating temperatures varying from 0.8 keV to > 3 keV. We have fitted these spectra with non-equilibrium ionization models and found that all regions are best fitted by emission from a hot plasma underabundant in metals (<0.25 solar), but in some cases fluorescent emission indicates overabundances of Ar and Fe. The ionization stage of the metals appears to be far from equilibrium, at some spots as low as log (n_et) (m(-3) s) ~ 15.3. We discuss the physical reality of the abundances and suggest an electron distribution with a supra-thermal tail to alleviate the strong depletion factors observed. We argue that RCW86 is the result of a cavity explosion.