ASCA Observations of the Supernova Remnant G156.2+5.7

Abstract

We report on the ASCA X-ray spectra from the north rim and the center of the supernova remnant (SNR) G156.2+5.7. The spectra are found to comprise soft and hard X-ray components. No clear shell structure has been found, either in the soft or in the hard X-ray bands. The soft X-rays are attributable to a non-equilibrium ionization plasma with a temperature of 0.4 keV and an ionization timescale of 1011.0−11.2 cm−3s. A Sedov solution with an explosion energy of 1051 erg leads to an age of ∼ 1.5 × 104 yr and a density of ambient gas of ∼ 0.2 cm−3. The distance to G156.2+5.7 is estimated to be ∼ 1.3 kpc. The abundances of silicon and sulfur vary between the center and the north rim of the SNR, while the abundances of all other elements do not. The hard component can be modeled with either thermal emission of a temperature higher than a few keV or a non-thermal process with a power-law spectrum of photon index 1.5–1.8. Since the former model requires an uncomfortably high temperature, we favor a non-thermal model. We also discuss the nature of a point source found at the edge of the SNR.