Before creating a new event, i usually check to see maybe a standard one is raised, go to transaction SWELS and turn the event trace on, now send an idoc into the system and see if there are events raised in transaction SWEL.
If not the next step is to see if there are change documents written when the object (article) is created, if so, you can raise an event from the change documents (transaction SWEC - there is also a wizard).
if not the link in my first reply was to the help on how to create an event from the idoc processing - have you tried it?
Now, if you don't have an event you can enhance your object , see:
Extending Object Types: Inheritance and Delegation (SAP Library - Business Task Management)
