2022PASJ...74..656S

In this paper, we investigate the Fe K-shell lines in the supernova remnant W 51 C and hard X-ray sources in the proximity. We measure the intensities of the Fe I Kα and Fe XXV Heα lines at 6.40 and 6.68 keV, respectively, and find that the intensity of the 6.68 keV line is consistent with the background level expected from previous studies, while that of the 6.40 keV line is higher at the significance level of 2.0σ. Given the presence of gamma-ray emission and high ionization rate point spatially coincident with the remnant, we conclude that the enhanced 6.40 keV line most likely originates from the interaction between low-energy cosmic rays and molecular clouds. Also, we discover an enhanced 6.68 keV line emission from the compact H II region G49.0-0.3 at a significance level of 3.4σ. Spectral analysis reveals that the temperature and abundance of the thermal plasma with the 6.68 keV line is kT = 3.0^+0.8_–0.7 keV and Z = 0.5 ± 0.2 solar, respectively. These values are explained by the thermal plasma generated by the stellar winds of O stars.