It's not fake, I've seen numerous photos of this effect. And they DO fly that low - I know it seems crazy but I've watched them in person. The vapor cone effect CAN occur when breaking the sound barrier but ALSO occurs at lower speeds:

http://wilk4.com/misc/soundbreak.htm

I love how ABSOLUTELY CERTAIN people are that this is fake when they really don't know for sure.

After going to the NASA site I can see I was wrong, but for a while I was CERTAIN this was a viral ad for the Energizer Bunny.