Author Rank is a term Google uses to remember you as an author of the content you have produced. It takes years to build a recognition as an author, especially when you've built a great website and its content. But suppose you sell it one day, then you lose the content and the recognition that you are a good writer because your content now belongs to some one else. But Google retains the knowledge of what you have done as a writer by accumulating the data from your owned websites. You will of course need to provide more content on newer sites to maintain your AuthorRank.
Google now associates your content with you through the AuthorRank. Google more on this term to learn it in details. It is actually an easy to understand concept when you read it in details. there are various important aspects like involvement of your earlier backlinks, your involvement on Google+, any citations given to you by any authority sites, your authority on social platforms, your comments, and so on will decide what AuthorRank Google gives you.