JSTOR isn't giving me results for either, but I did find at least one paper that cites each of those, so despite the names (B.S. de Witt, really?) I suppose they are actually real papers.

(Or else the astrophysics community has been bamboozled by Diane Duane, which honestly wouldn't shock me.)

ooh, and I did find the abstract of the Gott paper on Ebsco/Nature.com, but I don't have access to the full text alas.

Hopefully trouble will have more luck!