RGS Observations of Ejecta Knots in Tycho's Supernova Remnant

TL;DR

This study uses XMM-Newton/RGS observations to analyze ejecta knots in Tycho's supernova remnant, detecting emission lines and measuring line broadening to infer high temperatures and reverse shock heating of supernova ejecta.

Contribution

First detection of oxygen lines in Tycho's SNR and detailed spectral analysis revealing ejecta composition and shock heating processes.

Findings

Detected O, Ne, Si, Fe emission lines in knots

Measured line broadening indicating high thermal temperatures

Confirmed knots are heated by reverse shock containing supernova ejecta

Abstract

We present results from {\it XMM-Newton/RGS} observations of prominent knots in the southest portion of Tycho's supernova remnant, known to be the remnant of a Type Ia SN in 1572 C.E. By dispersing the photons from these knots out of the remnant with very little emission in front of or behind them, we obtained the nearly uncontaminated spectra of the knots. In the southernmost knot, the RGS successfully resolved numerous emission lines from Si, Ne, O He$\alpha$ and Ly$\alpha$, and Fe L-shell. This is the first clear detection of O lines in Tycho's SNR. Line broadening was measured to be $\sim 3$ eV for the O He$\alpha$ and $\sim 4.5$ eV for Fe L lines. If we attribute the broadening to pure thermal Doppler effects, then we obtain kT$_{O}$ and kT$_{Fe}$ to be $\sim 400$ keV and 1.5 MeV, respectively. These temperatures can be explained by heating in a reverse shock with a shock velocity of $\sim 3500$ km s$^{-1}$. The abundances obtained from fitting the RGS and MOS data together imply substantially elevated amounts of these materials, confirming previous studies that the knots are heated by a reverse shock, and thus contain ejecta material from the supernova. We are unable to find a Type Ia explosion model that reproduces these abundances, but this is likely the result of this knot being too small to extrapolate to the entire remnant.