Most of the information - at least as taught in Russia - related to how Rurik Dynasty became rulers of Rus is based on "Повѣсть времяньныхъ лѣтъ" ("Tale of Bygone Years", aka "Primary Chronicle").
Is there modern historical research into this topic that is based on documents other than that one (e.g. some western documents/accounts, or any non-Slavic ones)?
Rurik Wiki has some hints of possible theories, but doesn't seem to list too many primary references (only some Russian research in the first reference).