Ownt^4 is simply what it implies--Someone just got owned four times more than the Ownee's interpretation of "Ownt".
Mathematically it looks like this: Ownt * Ownt * Ownt * Ownt = Ownt^4
Since "Own", "Ownt" and "Pwnt" are variables to just how much something was owned, Ownt^4 cannot be simplified any farther mathematically.
Now, lets say Richard was in the middle of a Kill-frenzy, but then Zach snuck up right behind him and killed him with the SMG. Richard would've been Ownt^4.