2001AJ....121..591B

We report on an XMM-Newton observation of the most distant known quasar, SDSSp J104433.04-012502.2, at z=5.80. We have detected this quasar with high significance in the rest-frame 3.4-13.6 keV band, making it the most distant cosmic object detected in X-rays; 32±9 counts were collected. SDSSp J104433.04-012502.2 is notably X-ray-weak relative to other luminous, optically selected quasars, with α_ox=-1.91±0.05 and a 3.4-13.6 keV luminosity of ~1.8x10⁴⁴ ergs.s^–1. The most likely reason for its X-ray weakness is heavy absorption with N_H≳10²⁴ cm^–2, as is seen in some broad absorption line quasars and related objects; we discuss this and other possibilities. High-quality spectroscopy from 0.95-1.10 µm to search for blueshifted C IV absorption may elucidate the origin of the X-ray weakness.