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 $\sim {4{}^{\mathrm {\prime }}}$. The spectrum shows a featureless continuum, and can thus be fitted by a power-law model of $\Gamma \sim 2.2$ with an absorption of $N_{\mathrm{H}} \sim 5.2 \times 10^{22} \,\mathrm{cm}^{-2}$. From this $N_{\mathrm{H}}$ value, we estimated the distance to G32.45$+$0.1 to be $\sim 17 \,\mathrm{kpc}$. Thus, the luminosity (in the 0.5–10.0 keV band) and radius of the shell are $\sim 9.5 \times 10^{34} \,\mathrm{ergs} \,\mathrm{s}^{-1}$ and $\sim 20 \,\mathrm{pc}$, respectively. The radio complex sources in the NRAO/VLA Sky Survey (NVSS; 1.4 GHz) 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 (0.5–10.0 keV) is estimated to be $9.0 \times 10^{-13} \,\mathrm{ergs} \,\mathrm{cm}^{-2} \,\mathrm{s}^{-1}$, which is consistent with the ASCA result.