A Suzaku Study of Ejecta Structure and Origin of Hard X-Ray Emission in the Supernova Remnant G 156.2+5.7

Abstract

Abstract We report on an X-ray study of the evolved Galactic supernova remnant (SNR) G 156.2$+$5.7 based on six pointing observations with Suzaku. The remnant’s large extent (100$'$ in diameter) allows us to investigate its radial structure in the northwestern and eastern directions from the apparent center. The X-ray spectra were well fit with a two-component non-equilibrium ionization model representing the swept-up interstellar medium (ISM) and the metal-rich ejecta. We found prominent central concentrations of Si, S, and Fe from the ejecta component; the lighter elements of O, Ne, and Mg were distributed more uniformly. The temperature of the ISM component suggests a slow shock ($\sim $610–960 km s$^{-1}$); hence, the remnant’s age is estimated to be $\sim $7000–15000 yr, assuming its distance to be $\sim $1.1 kpc. G 156.2$+$5.7 has also been thought to emit hard, non-thermal X-rays, despite being considerably older than any other such remnant. In response to a recent discovery of a background cluster of galaxies (2XMM J045637.2$+$522411), we carefully excluded its contribution, and reexamined the origin of the hard X-ray emission. We found that the residual hard X-ray emission is consistent with the expected level of the cosmic X-ray background. Thus, no robust evidence for non-thermal emission was obtained from G 156.2$+$5.7. These results are consistent with the picture of an evolved SNR.