As part of the Dark Hours raid, there are a set of keys scattered throughout the area in hidden chests. Each key can be stacked, and once you have 6, you can open a chest after defeating the final boss that offers a chance to gain a number of Exotic weapons, including the new Assault Rifle: Eagle Bearer. Obtaining the Eagle Bearer is a 10% chance, while the end boss also drops them (around 3% chance). If you run each boss every week, and another after reset, you can pretty much farm the chest, even with alts.