Discovery of non-thermal X-rays from the shell of RCW 86

We report the ASCA (Advanced Satellite for Cosmology and Astrophysics) results of RCW 86, a shell-like supernova remnant (SNR). The bright region in the X-ray band traces the radio clumpy shell, although details of the structure are different. The X-ray spectrum from each part of the shell can not be fitted to a thin thermal plasma model, but requires at least three components: a low-temperature plasma of 0.3 keV, a high-temperature plasma of greater than or equal to several keV, and a power-law component with a photon index of similar to 3. The abundances of O, Ne, Mg, and Si are significantly higher than that of Fe, indicating that RCW 86 is a type II SNR. The absorption column of similar to 3 x 10(21) H cm(-2) indicates the distance to the SNR to be several kpc. The power-law component can be interpreted to be synchrotron radiation of high-energy electrons. Assuming an energy density equipartition between the magnetic field and the electrons, and using the radio and X-ray spectra, we argue that high-energy electrons are accelerated up to 20 TeV. The acceleration efficiency is, however, different from shell to shell.