Abstract
Abstract 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 ∼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 Lyα, O Lyα, 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 ⊙ , O / H = 0.5 ± 0.1 O / H ⊙ , Ne / H = 0.9 ± 0.1 Ne / H ⊙ , Mg / H = 1.0 ± 0.1 Mg / H ⊙ , Si / H = 1.0 ± 0.2 Si / H ⊙ , and Fe / H = 1.3 ± 0.1 Fe / H ⊙ . 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 O is obtained to be N / O = 6.8 − 2.1 + 2.5 N / O ⊙ . 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 ⊙ ≲ M ≲ 20 M ⊙.
Highlights
RX J1713.7-3946 is a shell-type supernova remnant (SNR) discovered by the ROSAT All-Sky Survey (Pfeffermann & Aschenbach 1996)
The abundance ratio of N to O is obtained to be N/O = 6.8+−22..51 (N/O). 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 M 20 M
We discovered a possible N-rich circumstellar material (CSM) knot inside the synchrotron-dominated SNR RX J1713.7-3946
Summary
RX J1713.7-3946 is a shell-type supernova remnant (SNR) discovered by the ROSAT All-Sky Survey (Pfeffermann & Aschenbach 1996). X-ray measurements of the expansion velocity suggest that this SNR is 1,580-2,800 years old (Tsuji & Uchiyama 2016; Acero et al 2017a) This age, combined with its location, led to a possible relation to SN 393 recorded in Chinese history books (Wang et al 1997). This SNR can be seen in wide-band wavelengths from radio (Slane et al 1999; Ellison et al 2001; Lazendic et al 2004; Sano et al 2020) to very-high-energy gamma rays
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