Can Google Bot Crawl authenticated pages? I am using Organic Groups and most of the pages i.e Discussions and related pages are only accessible to an authenticated user, can google bot crawl all these pages as well or is thrown a 403 error ?
Drupal will send a 403 response for any protected pages to any user agent, including the Googlebot, unless that user agent has been authenticated by Drupal and has a valid session cookie.

If your pages are only accessible by users with the "authenticated user" role, Google will not be able to crawl them.