The Alien Rifle is a type of projectile weapon contained in a case within the Quarantine Enforcement Platform.
The style of the weapon is unlike Precursor technology seen elsewhere, meaning it is likely that this weapon, or the technology used to create it, was taken from, or based on, another alien civilization.
Strong resemblance to human weaponry in form, this device must have been designed with a humanoid user in mind. Whether the aliens that built this structure were themselves humanoid or otherwise employed the use of humanoids is unclear. What is clear is that they considered defending this facility a necessary precaution. There is no obvious way to remove the rifle from the case.