Possible Detection of X-Ray Emitting Circumstellar Material in the Synchrotron-Dominated Supernova Remnant RX J 1713.7-3946

TL;DR

This study reports the discovery of an X-ray emitting circumstellar material knot in the supernova remnant RX J1713.7-3946, revealing details about the progenitor star's evolution and composition.

Contribution

First detection of a circumstellar material knot in RX J1713.7-3946 using high-resolution X-ray spectroscopy, providing insights into the progenitor star's mass and chemical enrichment.

Findings

The knot shows enhanced nitrogen abundance indicating circumstellar origin.

The elemental abundances suggest the progenitor was a 15-20 solar mass red supergiant.

The spectrum is well modeled by an absorbed thermal emission with a temperature of 0.65 keV.

Abstract

We report on a discovery of an X-ray emitting circumstellar material knot inside the synchrotron dominant supernova remnant (SNR) 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 $\sim$40$^{\prime\prime}$ 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 $k_{\rm B}T_{\rm e} = 0.65\pm 0.02$ keV. The elemental abundances are obtained to be ${\rm N/H} = 3.5\pm 0.8{\rm \left(N/H\right)_{\odot}}$, ${\rm O/H} = 0.5\pm0.1{\rm \left(O/H\right)_{\odot}}$, ${\rm Ne/H} = 0.9\pm0.1{\rm \left(Ne/H\right)_{\odot}}$, ${\rm Mg/H} = 1.0\pm0.1{\rm \left(Mg/H\right)_{\odot}}$, ${\rm Si/H} = 1.0\pm0.2{\rm \left(Si/H\right)_{\odot}}$, and ${\rm Fe/H} = 1.3\pm0.1{\rm \left(Fe/H\right)_{\odot}}$. The enhanced N abundance with others being about the solar values allows us to infer that this knot is circumstellar material ejected when the progenitor star evolved into a red supergiant. The abundance ratio of N to O is obtained to be $\rm N/O = 6.8_{-2.1}^{+2.5}\left(N/O\right)_{\odot}$. 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 $15\, \rm M_{\odot} \lesssim \rm M \lesssim 20\, \rm M_{\odot}$.