Thermal and nonthermal X-ray emission in supernova remnant RCW 86

Supernova remnants may exhibit both thermal and nonthermal X-ray emission. Such remnants can be distinguished by the weakness of their X-ray lines bec ause of the presence of a strong nonthermal X-ray continuum. RCW 86 is a re mnant with weak lines, resulting in low and peculiar abundances when therma l models alone are used to interpret its X-ray spectrum. This indicates the presence of a strong nonthermal synchrotron continuum. We analyze ASCA X-r ay spectra of RCW 86 with the help of both nonequilibrium ionization therma l models and nonthermal synchrotron models. A two-temperature thermal model and a simple nonthermal model with an exponential cutoff (plus interstella r absorption) give reasonable results. We obtain a blast-wave velocity of 8 00 km s(-1), a shock ionization age of 1x10(11)-3x10(11) cm(-3) s, and the break in nonthermal spectra at 2x10(16)-4x10(16) Hz. The strength of the no nthermal continuum correlates well with the radio brightness in the bright southwest section of the remnant. This is convincing evidence for X-ray syn chrotron emission in RCW 86.