I was wondering the same thing. In The Reef 2 (ghost fragment card), it talks about the Techeuns and some sort of technology (or magic) being employed by the Queen. She hears what are (presumably) the voices of fallen from the House of Wolves. There is a vision (or a hologram) and then the Queen speaks as if sending out a message to Skolas. I assume the message was sent out like the one from Petra in the cinematic intro to HoW. I think the harbingers are probably just advanced warships in the Awoken's arsenal.