  We report 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 reasonable fit to the
spectrum, suggesting a non-thermal origin. Together with the similarity to
SN1006, we propose that RX J1713.7-3946 is the second example, after SN1006, of
a synchrotron X-ray radiation from a shell of SNRs. Since the synchrotron
X-rays suggest existence of extremely high energy charged particles in the SNR
shell, our discovery should have strong impact on the origin of the cosmic
X-rays.
