XMM-Newton Observations of G32.45+0.1 and G38.55+0.0: Diffuse Hard X-Ray Sources Found by the ASCA Galactic Plane Survey

Abstract

We report on XMM-Newton observations of G32.45+0.1 and G38.55+0.0. These were discovered as diffuse hard X-ray sources by the ASCA Galactic Plane Survey, but the limited spatial resolution of ASCA could not conclude whether these are truly diffuse or a group of unresolved point-sources. XMM-Newton, with higher spatial resolution than ASCA, confirmed that G32.45+0.1 has a diffuse shell-like structure with a radius of ∼ 4'. The spectrum shows a featureless continuum, and can thus be fitted by a power-law model of Γ ∼ 2.2 with an absorption of N_H ∼ 5.2 × 10²² cm^-2. From this N_H value, we estimated the distance to G32.45+0.1 to be ∼ 17 kpc. Thus, the luminosity (in the 0.5-10.0keV band) and radius of the shell are ∼ 9.5 × 10³⁴ ergs s^-1 and ∼ 20 pc, respectively. The radio complex sources in the NRAO/VLA Sky Survey (NVSS; 1.4GHz) are globally associated with the X-ray shell of G32.45+0.1. Therefore, G32.45+0.1 is likely to be a synchrotron-dominant shell-like SNR. No significant diffuse structure was found in the XMM-Newton image of another ASCA diffuse source, G38.55+0.0. The upper limit of the observed flux (0.5-10.0keV) is estimated to be 9.0 × 10^-13 ergs cm^-2 s^-1, which is consistent with the ASCA result.