Possible Detection of X-Ray Emitting Circumstellar Material in the Synchrotron-dominated Supernova Remnant RX J1713.7-3946

We report on a discovery of an X-ray emitting circumstellar material (CSM) knot inside the synchrotron dominant supernova remnant RX J1713.7-3946. This knot was previously thought to be a Wolf-Rayet star (WR 85), but we realized that it is in fact similar to 40 '' away from WR 85, indicating no relation to WR 85. We performed high-resolution X-ray spectroscopy with the Reflection Grating Spectrometer (RGS) on board XMM-Newton. The RGS spectrum clearly resolves a number of emission lines, such as N Ly alpha, O Ly alpha, Fe XVIII, Ne X, Mg XI, and Si XIII. The spectrum can be well represented by an absorbed thermal-emission model with a temperature of k(B)T(e) = 0.65 +/- 0.02 keV. The elemental abundances are obtained to be N/H = 3.5 +/- 0.8(N/H)(circle dot), O/H = 0.5 +/- 0.1(0/H)(circle dot), Ne/H = 0.9 +/- 0.1(Ne/H)(circle dot), Mg/H = 1.0 +/- 0.1 (Mg/H)(circle dot), Si/H = 1.0 +/- 0.2(Si/H)(circle dot), and Fe/H = 1.3 +/- 0.1(Fe/H)(circle dot). The enhanced N abundance with others being about the solar values allows us to infer that this knot is CSM ejected when the progenitor star evolved into a red supergiant. The abundance ratio of N to 0 is obtained to be N/O = 6.81(-2.1)(+2.5)(N/O)(circle dot). By comparing this to those in outer layers of red supergiant stars expected from stellar evolution simulations, we estimate the initial mass of the progenitor star to be 15 M-circle dot less than or similar to M less than or similar to 20 M-circle dot.

Automated summary

This study reports the discovery of an X-ray emitting circumstellar material knot inside the synchrotron dominant supernova remnant RX J1713.7-3946, and provides details on its temperature, elemental abundances, and inferred progenitor star mass through high-resolution X-ray spectroscopy observation.