Quasar BTC40 J1429+011, Magnitude: 19.40, z=4.84 (missed it by that much!)

[PMSchu]

Dennis, that is SO close! Some of the bright stars aren't prefectly aligned either, but they're much larger, so the true position is harder to determine. It doesn't look like there's a similar artifact elsewhere on your image, but the mystery object is right at the detection limit of the exposures. Funny that the artifact appears where the quasar should be, or close anyway. I suppose that's how those things work.

Perhaps another 60x60 seconds of exposures will answer the question. When in doubt - collect more data.

Phil S.