Speaker
Description
Several extragalactic Fast X-ray transients (FXTs), detected as bursts of soft X-ray photons with durations of hundreds of seconds by the Einstein Probe mission, have recently been linked to the collapse of a massive star. For those FXTs, the ensuing supernovae are similar to those associated with long gamma-ray bursts (long-GRBs). Under the fireball model for long-GRBs, the collapse of a rapidly rotating, stripped envelope, massive star gives rise to a relativistic jet that powers the gamma-ray burst. It has been proposed that a population of fireball explosions exists with lower-energy, less relativistic, jets than those of typical GRBs, so-called dirty fireballs. It has been suggested that some FXTs could probe this previously elusive regime.
Here, we report on EP241026b, an FXT discovered at redshift z~2.3 with a delayed afterglow light curve peak. We model the optical and X-ray light curves using a tophat jet model and investigate the origin of the long-lasting X-ray plateau phase. We conclude that EP241026b is driven by a mildly relativistic outflow with a Lorentz factor of the jet of ~22, which is among the lowest detected for GRBs and FXTs to date. The low Lorentz factor, long X-ray plateau phase, and absence of a detection in gamma-rays provide compelling observational evidence for a dirty fireball explosion as the origin of EP241026b.
| Talk category | Plenary |
|---|---|
| Second preference | NOVA Network 3 |
