Progenitor constraint with circumstellar material for the magnetar-hosting supernova remnant RCW 103

Stellar winds blown out from massive stars ($\gtrsim 10M_{\odot }$) contain precious information on the progenitor itself, and in this context, the most important elements are carbon ©, nitrogen (N), and oxygen (O), which are produced by the CNO cycle in the H-burning layer. Although their X-ray fluorescence lines are expected to be detected in swept-up shock-heated circumstellar materials (CSMs) in supernova remnants (SNRs), particularly those of C and N have been difficult to detect so far. Here, we present a high-resolution spectroscopy of a young magnetar-hosting SNR RCW~103 with the Reflection Grating Spectrometer (RGS) onboard XMM-Newton and report on the detection of \ion{N}{7} Ly$\alpha$ (0.50~keV) line for the first time. By comparing the obtained abundance ratio of N to O (N/O$=3.8\pm 0.1$) with various stellar evolution models, we show that the progenitor of RCW~103 is likely to have a low-mass (10–12~$M_{\odot }$) and medium-rotation velocities ($\lesssim 100\mathrm{k}\mathrm{m}{\mathrm{s}}^{-1}$). The results also rule out the possibility of dynamo effects in massive ($\ge 35M_{\odot }$) stars as a formation mechanism of the associated magnetar 1E~161348$-$5055. Our method is useful for estimating various progenitor parameters for future missions with microcalorimeters such as XRISM and Athena.