2025ApJ...995..155K

Shell burning and internal mixing in massive stars play an important role in setting the initial conditions for core-collapse supernova explosions. In the late stages of stellar evolution, intense shell burning can cause distinct convective regions to merge, fundamentally restructuring the stellar interior. Although such phenomena are difficult to observe directly, the observation of “Mg-rich” supernova remnants (SNRs) has recently emerged as a potential signature of these events. In this study, we reanalyze X-ray observations of J0550-6823, a SNR in the Large Magellanic Cloud (LMC) and a new candidate Mg-rich SNR. Our spectral analysis confirms a low Ne/Mg mass ratio of ≈1 and its classification as Mg-rich. By comparing the observational results with presupernova models, we suggest that the progenitor of J0550-6823 likely had an extended convective shell that reduces the Ne/Mg ratio prior to its explosion. Furthermore, we observe that ∼2-3 Mg-rich SNRs exist in the LMC, suggesting that ≲10%-40% of massive stars in the LMC may have had an extended convective shell, similar to what we observed in J0550-6823. This fraction would be important for understanding the final stages of the evolution of massive stars and Galactic chemical evolution.