Discovery of non-thermal X-rays from the northwest shell of the new SNR RX J1713.7-3946: The second SN 1006?

We report on the ASCA results of a featureless X-ray spectrum from RX J1713.7-3946, a new shell-like SNR discovered with the ROSAT all-sky survey. The northwest part of RX J1713.7-3946 was in the field of the ASCA Galactic Plane Survey Project, and was found to exhibit a shell-like structure. The spectrum, however, shows neither line emission nor any signature of a thermal origin. Instead, a power-law model with a photon index of 2.4-2.5 gives a reasonable fit to the spectrum, suggesting a non-thermal origin. Together with the similarity to SN 1006, we propose that RX J1713.7-3946 is the second example, after SN 1006, of synchrotron X-ray radiation from a shell of SNRs. Since the synchrotron X-rays suggest the existence of extremely high energy charged particles in the SNR shell, our discovery should have a strong impact on the origin of cosmic X-rays.