Dude, that's a big rat.
Nah. That's a small rat. The mouse we caught in our attic was quite a bit bigger.
Biggest rat I've ever seen was on the campus of Georgia Tech -- saw it under a trash can. I don't think a cat would take the thing on -- it was bigger than most cats. And no, it wasn't an oppossum -- I've seen plenty of those too (mostly splat'd on the road; but I've seen a couple alive).