The XRISM First Light Observation: Velocity Structure and Thermal Properties of the Supernova Remnant N132D

TL;DR

This paper reports the first high-resolution X-ray spectral analysis of supernova remnant N132D using XRISM, revealing detailed velocity structures and thermal properties that inform its evolutionary state.

Contribution

It provides the first high-resolution spectral measurements of N132D, offering new insights into its velocity distribution and thermal state, advancing understanding of supernova remnant dynamics.

Findings

Fe Heα lines are substantially broadened indicating high ion temperatures.

Estimated reverse shock velocity ranges from -1000 to 3300 km/s.

Fe Lyα emission shows a redshifted velocity of about 890 km/s.

Abstract

We present an initial analysis of the X-Ray Imaging and Spectroscopy Mission (XRISM) first-light observation of the supernova remnant (SNR) N132D 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 $\sigma_v \sim 450$ km s$^{-1}$. The Fe He$\alpha$ lines are, on the other hand, substantially broadened with $\sigma_v \sim 1670$ 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 He$\alpha$ 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 $-1000 \lesssim V_{\rm rs}~[{\rm km s}^{-1}] \lesssim 3300$ (in the observer frame). We also find that Fe Ly$\alpha$ emission is redshifted with a bulk velocity of $\sim 890$ km s$^{-1}$, substantially larger than the radial velocity of the local interstellar medium surrounding N132D. These results demonstrate that high-resolution X-ray spectroscopy is capable of providing constraints on the evolutionary stage, geometry, and velocity distribution of SNRs.