RGS Observations of Ejecta Knots in Tycho's Supernova Remnant

We present results from XMM-Newton/Reflection Grating Spectrometer (RGS) observations of prominent knots in the southernmost portion of Tycho's supernova remnant, known to be the remnant of a Type Ia supernova 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 FeL-shell. This is the first clear detection of O lines in Tycho's supernova remnant. Line broadening was measured to be similar to 3 eV for the O He alpha and similar to 4.5 eV for the FeLlines. If we attribute the broadening to pure thermal Doppler effects, then we obtainkT(O)andkT(Fe)to be similar to 400 keV and 1.5 MeV, respectively. These temperatures can be explained by heating in a reverse shock with a shock velocity of similar to 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.