Is it possible to send an event / from IONIC Web App (say PWA) to a mobile App (be it native/hybrid) without involving any other middleware

Well my actual requriement is to trigger Android Intent from web app to a native mobile app. Can this be achieved in any way?

You are looking for a deep link I guess. If the Android app is configured properly, you can link to a special URL that will open the app and navigate to the proper screen in the app.