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K.J. Borkowski (NCSU), J. Rho (IPAC/Caltech), K.K. Dyer, S.P. Reynolds (NCSU)
Supernova remnants may exhibit both thermal and nonthermal X-ray emission. Such remnants can be distinguished by the weakness of their X-ray lines, because of the presence of a strong nonthermal X-ray continuum. RCW 86 is a remnant with weak lines, resulting in low and peculiar abundances when thermal models alone are used to interpret its X-ray spectrum. This indicates the presence of a strong nonthermal synchrotron continuum.
We analyze ASCA X-ray spectra of RCW 86 with the help of both nonequilibrium ionization thermal models and nonthermal synchrotron models. A simple plane-parallel thermal shock model and a simple nonthermal model with an exponential cutoff (plus interstellar absorption) give reasonable results. We obtain approximately (~2/3--1) solar abundance, the shock ionization age of 1-2 \times 1011 cm-3s, and the break in nonthermal spectra at ~ 1017 Hz. More sophisticated models confirm these results, but the full separation of thermal and nonthermal contributions is not possible with the relatively low spectral resolution of ASCA. The strength of nonthermal continuum correlates well with the radio brightness in the bright SW section of the remnant. This is convincing evidence for X-ray synchrotron emission in RCW 86.