GB-1508-GREATER-THAN-4 RADIO-SELECTED QUASAR IN X-RAYS(5714, THE FIRST Z)

We report the detection in x ray of a high redshift (z=4.30) radio-lou d quasar, GB 1508 +/- 5714, the first radio-selected z>4 quasar seen i n x rays. The quasar was observed serendipitously with the Einstein ob servatory IPC at 0.02 +/- 0.003 counts s(-1). It is ten times brighter than the other two z>4 x-ray detected quasars. The x-ray source is un usually hard, implying either alpha(E)<-0.2, or N-H>10(22) atoms cm(-2 ) (1 sigma limits) for a simple power-law plus intrinsic (z=4.3) absor ption. Intrinsic absorption would make GB 1508 + 5714 similar to a lar ge fraction of z similar to 3 radio-loud quasars. (C) 1995 American As tronomical Society.