A name adopted by an author in his writings

One word substitution is Pseudonym.

Nickname: a familiar or humorous name given to a person or thing instead of or as well as the real name.
Pseudonym: a fictitious name, especially one used by an author.
Nomenclature: the devising or choosing of names for things, especially in a science or other discipline.
Title: a name that describes someone's position or job.