17K, 12 left, A9 from BB

[Casper05]

I don't play many MTTs, so I had no idea what to do here.

We are about 130K deep in this hand. Blinds are 1K/2K with 250 antes I think.

I'm in the BB with A9o. CO min raises to 4K. I call (this is prob a raise?).

Flop comes 779, he checks. I bet 10K, he raises to 50K, I fold. ???