Last year the German researcher Behnam Said published what may be the first monograph devoted specifically to jihadi anashid. It is based on his PhD thesis on the same topic. You may know Behnam’s work from the several excellent articles on anashid he has published in recent years. Behnam works in the German security service
Verfassungsschutz, and he was recently interviewed in the CTC Sentinel’s “View from the CT foxhole series”.
The book is in German, and I haven’t had the chance to read it yet, but Joas Wagemakers recently published a useful review of it in English. Joas writes that Behnam sets out to provide "a comprehensive (and perhaps even the definitive) treatment of the subject, a task in which he has largely succeeded.”