I was wormholed away from a planet but can't alert the aggressor?
An artifact was used on me to do it...

only disable, raid or hack can be alerted, I think, maybe I'm wrong.

Technically, the artifact was used on the planet, so you can't alert him.

You can alert someone that makes a successful invasion on one of your planets and (i think) who uses an artifact on a planet. the second i could be wrong about. I do know that you cannot alert someone who artifacts your ship (I've tried)