AK with top 2

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PokerStars No-Limit Hold'em, $0.10 BB (5 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

BB ($9.05)
Hero ($11.05)
MP ($7.80)
Button ($11)
SB ($10.10)

Preflop: Hero is UTG with K[img]/images/graemlins/club.gif[/img], A[img]/images/graemlins/club.gif[/img].
<font color="#CC3333">Hero raises to $0.5</font>, <font color="#666666">3 folds</font>, BB calls $0.40.

Flop: ($1.05) K[img]/images/graemlins/heart.gif[/img], 7[img]/images/graemlins/club.gif[/img], 7[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
BB checks, <font color="#CC3333">Hero bets $0.85</font>, BB calls $0.85.

Turn: ($2.75) A[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
BB checks, <font color="#CC3333">Hero bets $1.75</font>, <font color="#CC3333">BB raises to $5.3</font>, Hero??

Villan is unknown at this point. Hud hadn't even loaded stats on him yet. Bet size on the turn is a tad small I think, but what is the c/r range of an unknown here? Did the weak turn bet induce a bluff? Should I be folding top 2 here to unknowns?