Suzaku Observations of Fe K-shell Lines in the Supernova Remnant W51C and Hard X-ray Sources in the Proximity

TL;DR

This study uses Suzaku X-ray observations to analyze Fe K-shell lines in supernova remnant W51C and nearby sources, revealing interactions with cosmic rays and stellar wind effects.

Contribution

First detection of enhanced Fe K-line emission in W51C and its association with cosmic ray interactions and stellar wind plasma.

Findings

Enhanced 6.40 keV line likely from cosmic ray interactions with molecular clouds.

Enhanced 6.68 keV line from H II region G49.0-0.3 indicating thermal plasma.

Thermal plasma characterized by kT ≈ 3 keV and Z ≈ 0.5 solar.

Abstract

In this paper, we investigated the Fe K-shell lines in the supernova remnant W51C and hard X-ray sources in the proximity. We measured the intensities of Fe I K$\alpha$ and Fe XXV He$\alpha$ lines at 6.40 keV and 6.68 keV, respectively, and found 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 2.0${\sigma}$. 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 discovered an enhanced 6.68 keV line emission from the compact H II region G49.0-0.3 at the significance level of 3.4${\sigma}$. Spectral analysis revealed 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 $Z = 0.5 \pm 0.2$ solar, respectively. These values are explained by the thermal plasma generated by the stellar winds of O stars.