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 \pm 9 counts were collected .
SDSSp J104433.04–012502.2 is notably X-ray weak relative to other luminous , optically selected quasars , with \alpha _ { ox } = -1.91 \pm 0.05 and a 3.4–13.6 keV luminosity of \approx 1.8 \times 10 ^ { 44 } erg s ^ { -1 } .
The most likely reason for its X-ray weakness is heavy absorption with N _ { H } \lower 2.15 pt \hbox { $ \buildrel > \over { \sim } $ } 10 ^ { 24 } 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 \mu m to search for blueshifted C iv absorption may elucidate the origin of the X-ray weakness .