2023ApJ...950..137N

Stellar winds blown out from massive stars (≳10 M_⊙) contain precious information on the progenitor itself, and in this context the most important elements are carbon (C), 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 in supernova remnants, those of C and N have been particularly difficult to detect so far. Here, we present high-resolution spectroscopy of the young magnetar-hosting supernova remnant RCW 103 with the Reflection Grating Spectrometer on board XMM-Newton and report on the detection of the N VII Lyα (0.50 keV) line for the first time. By comparing the obtained abundance ratio of N to O (N/O = 3.8 ± 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_⊙) and medium rotation velocity (≲100 km s^–1). The results also rule out the possibility of dynamo effects in massive (≥35 M_⊙) stars as a mechanism for forming 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.