2002ApJ...569L...1S

We present X-ray and optical observations of CXOMP J213945.0-234655, a high-redshift (z=4.93) quasar discovered through the Chandra Multiwavelength Project (ChaMP). This object is the most distant X-ray-selected quasar published, with a rest-frame X-ray luminosity of L_X=5.9x10⁴⁴ ergs.s^–1 (measured in the 0.3-2.5 keV band and corrected for Galactic absorption). CXOMP J213945.0-234655 is a g' dropout object (>26.2), with r'=22.87 and i'=21.36. The rest-frame X-ray-to-optical flux ratio is similar to quasars at lower redshifts and slightly X-ray bright relative to z>4 optically selected quasars observed with Chandra. The ChaMP is beginning to acquire significant numbers of high-redshift quasars to investigate the X-ray luminosity function out to z∼5.