Discovery of a Pair of [CLC][ITAL]z[/ITAL][/CLC] = 4.25 Quasars from the Sloan Digital Sky Survey

We report the discovery of a pair of z = 4.25 quasars with a separation of 33arcseconds. The brighter of the two objects was identified as a high-redshiftquasar candidate from Sloan Digital Sky Survey multicolor imaging data, and theredshift was measured from a spectrum obtained with the Hobby-Eberly Telescope.The slit orientation of this observation {\it by chance} included anotherquasar, approximately one magnitude fainter and having the same redshift as thetarget. This is the third serendipitous discovery of a z > 4 quasar. Thedifferences in the relative strengths and profiles of the emission linessuggest that this is a quasar pair and not a gravitational lens. The twoobjects are likely to be physically associated; the projected physicalseparation is approximately 210 $h_{50}^{-1}$ kpc and the redshifts areidentical to $\approx$ 0.01, implying a radial physical separation of 950$h_{50}^{-1}$ kpc or less. The existence of this pair is strong circumstantialevidence that $z \sim 4$ quasars are clustered.Comment: 15 pages, 4 figures, submitted to A