EDP Sciences

Vol. 588
In section 1. Letters

First 3 mm-VLBI imaging of the two-sided jet in Cygnus A. Zooming into the launching region

by B. Boccardi, T.P. Krichbaum, U. Bach, M. Bremer, and J.A. Zensus A&A, 588, L9


For the first time, VLBI images have been obtained of the archetypal radio galaxy Cygnus A at the frequency of 86 GHz. The high spatial resolution gives insight into the transverse width profile at the onset of the two-sided flow. The jet base appears wide with a minimum width of 227 Schwarzschild radius RS. This is significantly larger than the radius of the innermost stable circular orbit (ISCO), suggesting that the emission is produced by a mildly relativistic, parabolically expanding outer disk wind. The existence of a central and faster jet, possibly driven by the rotation of the inner regions of the accretion disk or by the spinning black hole and invisible due to Doppler deboosting, is suggested by the kinematic properties and by the observed limb brightening of the flow.