How to catch an event - adding a bot to a conversation in vk api?

Question

API

I am making a bot for a conference, and the question arose, how to catch the event adding a bot to a conversation?
At the moment I'm getting a response like this from longpoll:

{"ts":"666","updates":[{"type":"message_new","object":{"date":11111111,"from_id":11111111,"id":0,"out":0,"peer_id":2000000001,"text":"текст","conversation_message_id":450,"fwd_messages":[],"important":false,"random_id":0,"attachments":[],"is_hidden":false},"group_id":11111111}]}

Further I already process this request. It is logical to assume that if there is a type "message_new", there should be a type that is responsible for adding a bot to the conversation, but I can not find something similar to this.
I would really appreciate an explanation.