Translation:A list of the authors is available here.
I don't think a possessive phrase can be indefinite in English: when you use the genitive construction (-'s) the possessed noun is automatically definite and any article is understood to refer to the possessor rather than the ‘possessee’—that is, in ‘a butcher's knife’, ‘a’ refers to ‘butcher’, not to ‘knife’ (it is ‘the knife of a butcher’, not ‘a knife of a/the butcher’). Since ‘authors’ is plural it can't take an indefinite article, so ‘an authors' list’ is ungrammatical. The funny thing is it doesn't immediately sound wrong because, when you read it out loud, it sounds like ‘an author's list’ (‘the list of an author’), which is a perfectly fine phrase, although not a correct translation. ‘A list of the authors’ is really the only possible translation.