Animating CrossBow


I have got a rigged model of a human being, who is supposed to cock a rigged CrossBow(pulling the bow back, so it is released with max force). Sine the CrossBow and the human being are seperate objects, I applied an Armature modifier to the bow of the Crossbow and added two vertex groups to the two bones of the bow of the Crossbow(one for the left bow side and one for the right bow side). However this would result into two seperate animations, since I have got two seperate armatures.Can someone please tell me how to do it correvtly so that I only end up with one animation?