Discovery of 6.4 keV line and soft X-ray emissions from G323.7-1.0 with Suzaku
Abstract
In this paper, the Suzaku X-ray data of the Galactic Supernova Remnant (SNR) candidate G323.7-1.0 are analyzed to search for X-ray emission. Spatially-extended enhancements in the 6.4 keV line and in soft X-rays are found inside or on the radio shell. The soft X-ray enhancement would be the hottest part of the shell-like X-ray emission along the radio shell. The 6.4 keV line enhancement is detected at a significance level of 4.1 σ. The lower limit of the equivalent width (EW) is 1.2 keV. The energy centroid of the 6.4 keV line is 6.40 0.04 keV, indicating that the iron is less ionized than the Ne-like state. If the 6.4 keV line originates from ionizing non-equilibrium thermal plasma, presence of iron-rich ejecta in a low-ionization state is required, which is disfavored by the relatively old age of the SNR. The 6.4 keV line enhancement would be due to K-shell ionization of iron atoms in a dense interstellar medium by high-energy particles. Since there is no irradiating X-ray source, the origin of the 6.4 keV line enhancement is not likely the photoionization. The large EW can only be explained by K-shell ionization due to cosmic-ray protons with an energy of 10 MeV, which might be generated by the shock acceleration in G323.7-1.0.