高能暂现源 · 每日文献综述

The explosion of a star is first marked by the shock wave breaking out of the stellar surface, producing a burst of ultraviolet and X-ray radiation. These events are observationally rare, despite likely accompanying the majority of supernovae (SNe). Here, we report on our multiwavelength observing campaign of the closest Einstein Probe fast X-ray transient (FXT) EP260321a at z = 0.0344. The thermal (kT = 130 eV) X-ray emission with peak luminosity of 1.0 × 10<SUP>45</SUP> erg s<SUP>−1</SUP> points to a shock breakout origin. We demonstrate that EP260321a is accompanied by a broad-lined Type Ic supernova, SN 2026gzf. The supernova (SN) properties, including its spectral evolution, lightcurve evolution, and expansion velocities, are all typical of the energetic stripped-envelope SNe associated with gamma-ray bursts (GRBs). However, deep X-ray upper limits obtained with the Chandra X-ray Observatory do not detect an X-ray afterglow, and instead exclude the afterglow of known GRBs or FXTs. If the stellar explosion launched a successful relativistic jet, we require that it had both a low Lorentz factor of Γ<SUB>0</SUB> &lt; 30 and a kinetic energy of E<SUB>kin</SUB> &lt; 10<SUP>49</SUP> erg for a stellar wind density of A<SUB>*</SUB> ≳ 1. We propose that EP260321a originated from a mildly relativistic, weak outflow that was choked by the progenitor star. This scenario is capable of naturally explaining its low X-ray luminosity and lack of prompt gamma-ray emission. EP260321a bridges the gap between SN 2008D and low-luminosity GRBs, suggesting a greater diversity in the physical parameters of stripped stars as they undergo terminal collapse.