AT2025ulz and S250818k: zooming in with the Hubble Space Telescope

Yu-Han Yang, Eleonora Troja, Marko Ristić +19

AT2025ulz is an optical/near-infrared transient discovered during follow-up of the candidate gravitational wave (GW) event S250818k. Its young age ($\lesssim$1 d), rapid decline an…