Detection of the neutral iron line from the supernova remnant W 49 B with Suzaku.

This article focuses on the detection and analysis of neutral iron line emission at 6.4 keV and excess emission at 8–9 keV in the supernova remnant (SNR) W 49 B using Suzaku X-ray observations. The 6.4 keV line, significantly detected in the north-west region where W 49 B interacts with a molecular cloud, is attributed to ionization of neutral iron by low-energy cosmic ray protons (LECRp) accelerated in the SNR shell, with an estimated proton energy density much higher than typical Galactic values. Additionally, an excess emission feature in the 8–9 keV band, possibly related to highly ionized iron transitions or charge exchange processes between iron ions and neutral hydrogen, was identified but remains uncertain due to spectral complexity. The study highlights the need for future high-resolution X-ray missions to clarify the origins of these spectral features and better understand particle acceleration and plasma conditions in SNRs interacting with molecular clouds.