The Superhero's World by Lucas Flint

A sudden attack from an alien race takes out hundreds of humanity's greatest superheroes, leaving the Earth defenseless in the face of an overwhelming foe. The only survivors are Kevin Jason (Bolt) and his friends, who are forced to ally with the government in order to protect the planet from the invading enemies.

Their mission becomes more urgent, however, when the aliens give humanity an ultimatum: Either surrender in forty-eight hours or be destroyed by the aliens' immense forces.

With only two days left to save the superhero community and the world in general, Kevin and his friends must defeat the aliens before the world is destroyed. Saving the world, however, will force Kevin and his friends to go to places no human has seen and force them to come to terms with an enemy unlike any they've faced before, one they may not be able to defeat.