2026ApJ...999..205H

We present the first analysis of the X-ray Imaging and Spectroscopy Mission (XRISM) observation of the supernova remnant (SNR) N103B. We fit the X-ray spectrum taken with the Resolve microcalorimeter, which captured emission lines from the predominantly ejecta elements Si, S, Ar, Ca, Cr, Mn, and Fe. Notably, our fits require a previously unidentified high-temperature, highly ionized, Fe-dominated plasma component with particularly high Cr and Mn abundances, matching a feature also present in the recent XRISM analysis of the SNR N132D. We find that all ejecta in N103B exhibits significant line broadening arising mostly from thermal Doppler broadening: increasing from σ_th ∼ 1700 km s^–1 for intermediate-mass element (IME: Si, S, Ar, and Ca) ejecta to ∼2800 km s^–1 for Fe-rich ejecta. These velocities correspond to reverse shock velocities of ∼3500 and ∼5900 km s^–1, respectively, in the ejecta frame of rest. Finally, we find that the IMEs are redshifted with a bulk velocity of ∼360 km s^–1 while the Fe-dominated components are split: one redshifted at ∼1560 km s^–1 and the other blueshifted at ∼1020 km s^–1. Our results provide further support for the double-ring structure of N103B as it expands into the bipolar winds of a nondegenerate companion and highlight the strength of high-resolution spectroscopic observations of SNRs.