When you find an artifact, you could add a 'treasurefound' variable...
that way, the event like would be
0 - Onactivate : client : ifvariable : treasurefound == 3 1 3
1 - Onvariabletrue : client : centerprint : Found etc.
2 - Onvariabletrue : player: additem : rewards
3 - Onvariabletrue : client : VCEmodvariable : treasurefound : set :0