Defeat one of Eramis's council members in an Empire Hunt.
Requires completion of the "Reclaiming Europa", "Empire's Fall" and "The Dark Priestess" quests.
Visit Variks in Charon's crossing to purchase Empire Hunts quests.
"Looks like there are some cracks in the empire now that Eramis is out. We can use that." —The Drifter
You found some briefs that indicate the Stasis weapon effort is being led by a high-ranking Fallen lieutenant. Taking the lieutenant down could gain you more information about the gun's whereabouts.