2025ApJ...993L..37O

The launch of the Einstein Probe unleashed a new era of high-energy transient discovery in the largely unexplored soft X-ray band. The Einstein Probe has detected a significant number of fast X-ray transients that display no gamma-ray emission, complicating their robust association with more common gamma-ray bursts. To explore their possible connection, we analyzed the redshift distribution of both Einstein Probe fast X-ray transients and long-duration gamma-ray bursts. A comparative analysis of their cumulative redshift distributions using nonparametric two-sample tests, namely the Kolmogorov-Smirnov and Anderson-Darling tests, finds no statistically significant difference. These tests favor that their redshifts are drawn from the same underlying distribution. This empirical connection between Einstein Probe transients and long gamma-ray bursts is further supported by their agreement with the so-called “Amati relation” between the spectral peak energy and the isotropic-equivalent energy. Together, these results indicate that most extragalactic Einstein Probe fast X-ray transients are closely related to long gamma-ray bursts and originate from a massive star (collapsar) progenitor channel. Our findings highlight the role of the Einstein Probe in uncovering the missing population of failed jets and dirty fireballs that emit primarily at soft X-ray wavelengths.