What happened to Odin? I started reading Thor comics recently, so I don't have a clue of what happened before 2013 stories. Odin doesn't appears at any story, he isn't at Asgard, and at most of the time isn't even mentioned. As far as I can see, Freya and Thor do most of the job he was supposed to do.  

Is he dead? If so, since when? Which story arc?