2025MNRAS.542.1125V

The remnants of supernova (SN) events display morphological properties intricately shaped by the progenitor star's stellar wind history, the distribution of the ambient medium, the magnetic field, and the characteristics of the explosion itself. Among these remnants, 3C 397 stands out with its distinctive rectangular morphology observed across radio, X-ray, and infrared wavelengths. Using magnetohydrodynamic simulations, we have investigated the evolution of this remnant and constrained its age to approximately 1 kyr, making it younger than previously estimated. We propose that its unique morphology arises from the expansion of the SNR into a circumstellar medium sculpted by the stellar wind of the SN companion star. Specifically, this stellar wind featured a dense, narrow equatorial region, forming a bipolar peanut-shaped cavity. On the one hand, the interaction of the expanding remnant with this cavity's boundaries plays a key role in developing its rectangular shape. On the other hand, our results indicate that interactions with a clumpy density distribution in the surrounding environment can influence the observed X-ray structure of the SNR 3C 397.