An [ITAL]XMM[/ITAL]-[ITAL]Newton[/ITAL] Detection of the [CLC][ITAL]z[/ITAL][/CLC] = 5.80 X-Ray–Weak Quasar SDSS[CLC]p[/CLC] J104433.04-012502.2

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 ≈1.8 × 10 44 ergs s -1 . The most likely reason for its X-ray weakness is heavy absorption with N H ≳ 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 μm to search for blueshifted C IV absorption may elucidate the origin of the X-ray weakness.