So I am sure this is eventually answered in the new book Prometheum Exxet, but as I dont have that book, I have to go by the core book. Also, as I would like to show the DM/GM something in writing, again, the answer to my question needs to come from the corebook...

Now to the question...

What exactly does the Artifact Advantage provide?

"The character possesses a mystical device of enormous power"

Effect: The player and the Game Master must agree on the abilities of the device. Spending additional points increases the capabilities of the object

Are there any sort of rules for this in the core book?

There are, but I have to say that I, personally, disagree with them. Artifacts are separated into different power levels, 1, 1+, 2, 2+, up to 5+. I am absolutely fine with this system, and think it is great to give GMs and players an idea of how powerful something is. However, it is very loose (almost nonexistent) with rules for creating artifacts outside of the game. It pretty much tells you to spend X CP, tell your GM what you want, and he will make it based on the power level that you are entitled to. Here is the part that I don't like: Your CP is worth different artifacts every 3 levels. 1-3 Level characters who use this advantage can get a 1+, 2, 2+ Artifact, while a Levels 7-9 get 2+, 3, 3+ artifacts. This makes it that if a character dies and the player creates a new character his CP is "worth" more than other characters who bought the Advantage at a lower level.

Where in the core book does it say this?

Forget everything I just said, as that comes from Promethium (I thought it said you wanted the answer from that).

Personally, I used https://docs.google.com/file/d/0B5tlaCQOd1OEZDRhZTkwNTMtZDE2OC00ODJkLThhOTQtYzhmZDIwNTI2MjU3/edit# to create any artifact that I needed for a character, and talked to the GM about other powers and such.

Thanks for this. This document looks interesting.

So then I assume, that technically, there are no "rules" in the core book regarding Artifacts?

None other than what is described in the advantage, as far as I know.