The First High-Resolution Grating Spectrum of a High-Redshift Quasar

Highredshift (z) quasars are the farthest persistently bright Xray pointsources in the universe. Although the high column densities towards highzquasars were observed in the early days of ROSAT, we still do not know whetherthis absorption is intrinsic to the quasar, or is due to intervening material,or whether the continuum is simply curved as to mimic absorption. So far,observations of such sources were limited to the moderate resolution of CCDspectra. We propose to obtain a high S/N 180 ks RGS spectrum of a highlyabsorbed yet extremely bright quasar RBS 315 (z 2.69) in order to finallyreveal the nature of its absorber: An outflow with absorption lines, the diffusephase of the intergalactic medium, or just curved continuum. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]