Ekaterina Koptelova (Graduate Institute of Astronomy, National Central University, Taiwan); Chorng-Yuan Hwang (Graduate Institute of Astronomy, National Central University, Taiwan)
Radio-loud quasars have been discovered up to a redshift of z~6.8, when the epoch of reionization was still ongoing. In the evolutionary scenario of radio galaxies, the radio-loud active galactic nuclei (AGNs) without strong emission lines in their spectra known as the BL Lacertae (BL Lac) objects, are older than radio-loud quasars and generally are not expected to exist at such early epochs of quasar-galaxy formation. We report the discovery of a radio-loud AGN at z>6 with a featureless optical spectrum and strong radio and optical variability typical for the known low-redshift BL Lac objects. This discovery may provide new constraints on the growth mechanisms and growth timescales of the most massive galaxies and their supermassive black holes within the first billion years after the Big Bang.