Plasma Diagnostics of the Supernova Remnant N132D Using Deep XMM-Newton Observations with the Reflection Grating Spectrometer

TL;DR

This study uses high-resolution X-ray spectroscopy to analyze the supernova remnant N132D, revealing multiple thermal plasma components, non-equilibrium ionization, and unusual line ratios suggesting complex physical processes.

Contribution

First detailed high-resolution X-ray spectral analysis of N132D revealing multiple plasma components and ionization states using XMM-Newton RGS data.

Findings

Detection of dozen emission lines from intermediate charge states.

Evidence of at least three thermal plasma components with different temperatures.

Unusual forbidden-to-resonance line ratios indicating complex plasma processes.

Abstract

We present XMM-Newton observations of N132D, the X-ray brightest supernova remnant (SNR) in the Large Magellanic Cloud (LMC), using the Reflection Grating Spectrometer (RGS) that enables high-resolution spectroscopy in the soft X-ray band. A dozen emission lines from L-shell transitions of various elements at intermediate charge states are newly detected in the RGS data integrating the ~200-ks on-axis observations. The 0.3-2.0-keV spectra require at least three components of thermal plasmas with different electron temperatures and indicate clear evidence of non-equilibrium ionization (NEI). Our detailed spectral diagnostics further reveal that the forbidden-to-resonance line ratios of O VII and Ne IX are both higher than expected for typical NEI plasmas. This enhancement could be attributed to either resonance scattering or emission induced by charge exchange in addition to a possible contribution from the superposition of multiple temperature components, although the lack of spatial information prevents us from concluding which is most likely.