Spatially Resolved Plasma Diagnostics of the Supernova Remnant DEM L71 using the Reflection Grating Spectrometer

TL;DR

This study demonstrates spatially resolved, high-resolution X-ray spectroscopy of the SNR DEM L71 using XMM-Newton's Reflection Grating Spectrometer to map line emission and perform region-by-region plasma diagnostics. By reconstructing line emission along the RGS dispersion axis and measuring fluxes for OVIII Lyα and OVII lines across nine regions, the authors constrain $kT_{ m e}$ and $n_{ m e}t$ with collisional ionization models and uncover elevated OVII $f$/$r$ ratios in multiple zones. They explore resonance scattering and charge exchange as mechanisms to explain these ratios, showing that plausible $N_{ m H}$ and $kT_{ m e}$ values can account for RS effects, while NEI+$ m CX$ models fit region 2 for reasonable EM$_{CX}$/EM$_{ISM}$ ranges. Overall, the work highlights the utility of the RGS for imaging spectroscopy of moderately diffuse objects and emphasizes the need to consider RS and CX when interpreting SNR line diagnostics.

Abstract

We present a spatially resolved high-resolution X-ray spectroscopy of the supernova remnant DEM L71 using the Reflection Grating Spectrometer (RGS) aboard XMM-Newton. Because of the large dispersion angle of the RGS, we are able to resolve individual emission lines and examine their spatial distributions within this moderately extended remnant. We derive line fluxes across different regions of DEM L71 and perform quantitative plasma diagnostics. Our analysis reveals that some regions have high forbidden-to-resonance ratios of O\emissiontype{VII} He$α$ lines, suggesting a non-negligible contribution from additional physical processes, such as charge exchange and/or resonance scattering. Our results demonstrate that the RGS has potential to serve as an outstanding X-ray imaging spectrometer for moderately diffuse objects.

Figures (10)

• Figure 1: Chandra ACIS image of DEM L71: red represents the 18--21 Å (0.60--0.68 keV) range, corresponding to the OVIII Ly$\alpha$ lines, while blue denotes the 12--17 Å (0.75 --1.0 keV) range, associated with FeXVII L$\alpha$ lines. We calculate line fluxes for each region bounded by solid white lines as discribed in Section \ref{['subsec:flux_ratio_map']}. The RGS dispersion direction is indicated by the white arrow. Alt text: Chandra image covering the RGS field-of-views of DEM L71.
• Figure 2: RGS images and spectra of DEM L71. (a) RGS images obtained with RGS 1 and 2, where the horizontal axis represents the dispersion angle and corresponding photon wavelength, and the vertical axis indicates the off-axis angle of the incident photons along the cross-dispersion axis. (b) RGS 1 (black) and RGS 2 (red) first-order spectra. Alt text: 13--23 angstrom RGS images and spectra.
• Figure 3: Close-up views of the RGS images around the (a) FeXVII L$\alpha$ (3d--2p), (b) OVIII Ly$\alpha$, (c) OVII He$\alpha$ resonance and (d) OVII He$\alpha$ forbidden. The solid contours in (a) and (b) represent the EPIC MOS band images corresponding to OVIII Ly$\alpha$ (18--21 Å or 0.60--0.68 keV) and FeXVII L$\alpha$ (12--17 Å or 0.75--1.0 keV), respectively. Alt text: Close-up views of the RGS images. The X-axis corresponds to the wavelength, and the Y-axis corresponds to the off-axis angle along the cross-dispersion direction.
• Figure 4: Comparison of line profiles obtained with the RGS and MOS. (a) Cross-dispersion and dispersion profiles of the Fe XVII L$\alpha$ (3d--2p) line at 15 Å. The count number for each bin is normalized by the total count number. MOS profiles are created with X-ray events in the range of 12--17 Å or 0.75--1.0 keV. (b) Same as (a) but for profiles of the OVIII Ly$\alpha$ lines. MOS profile are created with X-ray events in the range of 18--21 Å or 0.60--0.68 keV. Alt text: Eight line graphs.
• Figure 5: RGS spectra of (a) OVIII Ly$\alpha$, (b) OVII He$\alpha$ resonance and (c) OVII He$\alpha$ forbidden lines. The top panels present spectra extracted from the segment corresponding to the regions 1--3 in Figure \ref{['fig:ccd_image']}, the middle panels correspond to the regions 4--6, and the bottom panels correspond to the regions 7--9. The MOS2 profile for the region corresponding to each segmentation is shown by a solid red line. We create the MOS profile with X-ray events corresponding to the OVIII Ly$\alpha$ lines (18--21 Å or 0.60--0.68 keV). The segmentation of the emission region along the dispersion axis for each line is determined using Equation (\ref{['eq:RGS_LSF']}), with the boundaries of each region marked by gray dashed lines. The region numbers are labeled consistently with those in Figure \ref{['fig:ccd_image']}. Alt text: RGS spectrum for each region.