Exploring the connection between compact object mergers and fast X-ray transients. The cases of LXT 240402A and EP250207b

The connection between compact object mergers and some extragalactic fast X-ray transients (FXRTs) has long been hypothesised but never ultimately established. In this work, we investigate two FXRTs, the LEIA X-ray Transient LXT,240402A and the Einstein Probe EP,250207b, whose precise positions lie close to nearby (z!łesssim!0.1) quiescent galaxies with a negligible probability of chance coincidence, identifying them as particularly promising cases of merger-driven explosions in the local Universe. We used to derive accurate localisations for both events and secure otherwise ambiguous associations with their optical counterparts. Deep optical and near-infrared observations with VLT, GTC, and LBT were performed to characterise the surrounding environment and search for kilonova emission, the hallmark of neutron star mergers. Complementary early-time X-ray monitoring with and was used to constrain the non-thermal afterglow. Chandra Swift Einstein Probe We find that both FXRTs remain compatible with a compact binary merger progenitor, which produced low-mass ejecta and kilonova emission subdominant to the afterglow. However, alternative explanations such as a distant (z!≳!1) core-collapse supernova cannot be conclusively ruled out.