Yeah, you can use the OSGi Event Admin service if you want, but it has some limitations, mostly that it only support asynchronous topic semantics, without any delivery guarantee at all.
Anyway, from the console, use the following command:
karaf> osgi:install -s osgi:install -s mvn:org.apache.felix/org.apache.felix.eventadmin/1.2.6
Then you can use it according to the OSGi Spec.
It sounds great!
Thank you very much.