2026/07/27 by Akihiro Suzuki, Keiichi Maeda, Toshikazu Shigeyama
#astro-ph.HE
We present shock breakout (SBO) modeling of the recently discovered X-ray transient EP260321a detected by the Einstein Probe mission. Our semi-analytic model, based on our previous work, follows the interaction between a supernova ejecta with a mildly relativistic outer envelope and a dense, wind-like circumstellar medium (CSM) by using a thin-shell approximation that incorporates relativistic effects. We find that the observed properties of the X-ray emission are well explained by the breakout emission powered by a high-velocity envelope with a kinetic energy of ∼3.5×1049 erg (excluding the supernova ejecta) and a dense wind characterized by a mass-loss rate of M≃1.2× 10-3(vw/103 km s-1) M_\odot yr-1, where vw is the wind velocity. The observed burst duration requires the dense CSM to extend up to ∼350 R_\odot, corresponding to a CSM mass of ∼ 10-5 M_\odot. These results demonstrate that SBO observations provide a sensitive probe of mass loss from stripped-envelope supernova progenitors shortly before core collapse.