DISCOVERY OF A SUBPARSEC RADIO COUNTERJET IN THE NUCLEUS OF CENTAURUS-A

A subparsec scale radio counterjet has been detected in the nucleus of the closest radio galaxy, Centaurus A (NGC 5128), with VLBI imaging a t 2.3 and 8.4 GHz. This is one of the first detections of a VLBI count erjet and provides new constraints on the kinematics of the radio jets emerging from the nucleus of Cen A. A bright, compact core is seen at 8.4 GHz, along with a jet extending along P.A. 51 degrees. The core i s completely absorbed at 2.3 GHz. Our images show a much wider gap bet ween the base of the main jet and the counterjet at 2.3 GHz than at 8. 4 GHz and also that the core has an extraordinarily inverted spectrum. These observations provide evidence that the innermost 0.4-0.8 pc of the source is seen through a disk or torus of ionized gas which is opa que at low frequencies due to free-free absorption.