Or did he hit a set?

$0.05/$0.10 10 handed

SB - 14.23
BB - 3.26
UTG - 9.55
UTG+1 - 5.23
UTG+2 - 12.50
MP1 - 18.22
MP2 - 1.10
Hero - 12.86
CO - 15.42
Button - 5.83

Preflop - Hero is dealt A A
UTG calls, 2 folds, MP1 calls, MP2 calls, Hero raises to 0.50, CO calls, 3 folds, UTG calls, 3 folds, MP2 raises to 1.10 (all-in), Hero calls, CO calls, 1 fold

Flop - (Board 4 8 9)
Hero bets 3.00, CO raises to 8.00, Hero ??????

No reads