Players of fallout knows about the ultimate “Alien Blaster” a very special weapon which the put in every fallout game some of the instructions below will guide you to the way to acquire this sweet weapon.
First of all you need to go right by Oberland Station and head to this location on your map check the shot below if you are having trouble finding it
Then turn towards the woods you will be walking past some broken fences and keep going and then you will come across a wreckage of a ship.
Go down and you will see some green weird substance on the ground
Follow the trail and you will be able to find a cave , enter it and you will encounter an alien unfortunatly you have to kill the alien , that greenish substance is that alien’s blood and when you kill it you will be able to loot this baby ..
This is probably an Event in Fallout 4 , if you wont be able to find it there come back next time and then you will be able to find it .