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

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 $k_{\mathrm{B}}{T}_{\mathrm{e}}=0.65\pm 0.02$ keV. The elemental abundances are obtained to be $N/H=3.5\pm 0.8{\left(N/H\right)}_{\odot }$, $O/H=0.5\pm 0.1{\left(O/H\right)}_{\odot }$, $Ne/H=0.9\pm 0.1{\left(Ne/H\right)}_{\odot }$, $Mg/H=1.0\pm 0.1{\left(Mg/H\right)}_{\odot }$, $Si/H=1.0\pm 0.2{\left(Si/H\right)}_{\odot }$, and $Fe/H=1.3\pm 0.1{\left(Fe/H\right)}_{\odot }$. 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 $N/O=6.8_{-2.1}^{+2.5}{\left(N/O\right)}_{\odot }$. 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 $15{\mathrm{M}}_{\odot }\lesssim \mathrm{M}\lesssim 20{\mathrm{M}}_{\odot }$.

13 pages, 12 figures, 4 tables, accepted for publication in ApJ

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