Another tactical awareness test

Another tactical awareness test

hotwax
hotwax
Oct 7, 2016, 3:30 PM |
2

My higher rated opponent just played Rxa4, grabbing a pawn, thinking my b3 rook is hanging... What's the refutation? 

 
To be honest, I was extremely lucky in this game, since the move before, I was completely losing. Can you figure out what my opponent missed? 
 
 
The full game if anyone is interested (time control 15/10):