A Suzaku Study of Ejecta Structure and Origin of Hard X-ray Emission in the Supernova Remnant G156.2+5.7

TL;DR

This study uses Suzaku X-ray observations to analyze the structure, ejecta composition, and X-ray emission origins of the supernova remnant G156.2+5.7, revealing ejecta distribution and confirming its thermal emission nature.

Contribution

First detailed radial X-ray spectral analysis of G156.2+5.7, clarifying ejecta distribution and ruling out non-thermal X-ray emission in this evolved SNR.

Findings

Ejecta rich in Si, S, Fe concentrated centrally

Remnant's age estimated at 7,000-15,000 years

Hard X-ray emission consistent with cosmic background

Abstract

We report an X-ray study of the evolved Galactic supernova remnant (SNR) G156.2+5.7 based on six pointing observations with Suzaku. The remnant's large extent (100$\arcmin$ 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 (610-960 km s$^{-1}$), hence the remnant's age is estimated to be 7,000-15,000 yr, assuming its distance to be $\sim$1.1 kpc. G156.2+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 the non-thermal emission was obtained from G156.2+5.7. These results are consistent with the picture of an evolved SNR.