Discovery of an ionized FeK edge in the z=3.91 broad absorption line quasar APM 08279+5255 with XMM-Newton

Recent XMM-Newton observations of the high-redshift, lensed, broad absorption line (BAL) quasi-stellar object APM 08279+5255, one of the most luminous objects in the universe, allowed the detection of a high column density absorber (N-H approximate to 10(23) cm(-2)) in the form of a K-shell absorption edge of significantly ionized iron (Fe XV-Fe XVIII) and corresponding ionized lower energy absorption. Our findings confirm a basic prediction of phenomenological geometry models for the BAL outflow and can constrain the size of the absorbing region. The Fe/O abundance of the absorbing material is significantly higher than solar (Fe/O = 2-5), giving interesting constraints on the gas enrichment history in the early universe.