Suzaku Observations of Thermal and Non-Thermal X-Ray Emission from the Middle-Aged Supernova Remnant G156.2$+$5.7

Abstract

Abstract We present results from an 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 $\sim$ 50$^\prime$). 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 confirmed that the X-ray spectra consist of soft and hard-tail emissions, while in the eastern rim we found no significant hard-tail emission. The soft emission was well-fitted by a non-equilibrium ionization (NEI) model. In the central portion, a two-component (the interstellar medium and the metal-rich ejecta) NEI model was used to fit 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_\odot$. The origin of the hard-tail emission is highly likely to be 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 $\sim$ 500 kms$^{-1}$.