Suzaku Observations of Thermal and Non-Thermal X-Ray Emission from the
  Middle-Aged Supernova Remnant G156.2+5.7
  We present results from X-ray analysis of a Galactic middle-aged supernova
remnant (SNR) G156.2+5.7 which is bright and largely extended in X-ray
wavelengths, showing a clear circular shape (radius about 50'). Using the
Suzaku satellite, we observed this SNR in three pointings; partially covering
the northwestern rim, the eastern rim, and the central portion of this SNR. In
the northwestern rim and the central portion, we confirm that the X-ray spectra
consist of soft and hard-tail emission, while in the eastern rim we find no
significant hard-tail emission. The soft emission is well fitted by
non-equilibrium ionization (NEI) model. In the central portion, a two-component
(the interstellar medium and the metal-rich ejecta) NEI model fits the soft
emission better than a one-component NEI model from a statistical point of
view. The relative abundances in the ejecta component suggest that G156.2+5.7
is a remnant from a core-collapse SN explosion whose progenitor mass is less
than 15 M_solar. The origin of the hard-tail emission is highly likely
non-thermal synchrotron emission from relativistic electrons. In the
northwestern rim, the relativistic electrons seem to be accelerated by a
forward shock with a slow velocity of about 500 km/sec.
