The XRISM first-light observation: Velocity structure and thermal properties of the supernova remnant N 132D

We present an initial analysis of the X-Ray Imaging and Spectroscopy Mission (XRISM) first-light observation of the supernova remnant (SNR) N 132D in the Large Magellanic Cloud. The Resolve microcalorimeter has obtained the first high-resolution spectrum in the 1.6–10 keV band, which contains K-shell emission lines of Si, S, Ar, Ca, and Fe. We find that the Si and S lines are relatively narrow, with a broadening represented by a Gaussian-like velocity dispersion of σ_υ∼ 450  km s^-1⁠. However, the Fe Heα lines are substantially broadened with σ_υ∼ km s^-1. . This broadening can be explained by a combination of the thermal Doppler effect due to the high ion temperature and the kinematic Doppler effect due to the SNR expansion. Assuming that the Fe Heα
emission originates predominantly from the supernova ejecta, we estimate the reverse shock velocity at the time when the bulk of the Fe ejecta were shock heated to be - 1000 ^<_∼ (km s^-1) (in the observer frame). We also find that Fe Lyα emission is redshifted with a bulk velocity of ∼ 890 km s^-1⁠, substantially larger than the radial velocity of the local interstellar medium surrounding N 132D. These results demonstrate that high-resolution X-ray spectroscopy is capable of providing constraints on the evolutionary stage, geometry, and velocity distribution of SNRs.