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

TL;DR

This paper presents the first high-resolution 86 GHz VLBI images of Cygnus A, revealing detailed nuclear jet structures and providing constraints on jet launching mechanisms near the black hole.

Contribution

It offers the first 86 GHz VLBI imaging of Cygnus A's two-sided jet, analyzing jet width and launching regions at unprecedented resolution.

Findings

Jet base is wide, with a minimum width of about 227 Schwarzschild radii.

Outer accretion disk likely contributes to jet launching.

Evidence suggests a faster inner jet component possibly powered by black hole spin or disk rotation.

Abstract

We present for the first time Very-Long-Baseline Interferometry images of the radio galaxy Cygnus A at the frequency of $86$ $\rm GHz$. Thanks to the high spatial resolution of only ${\sim}200$ Schwarzschild radii ($R_{\bf S}$), such observations provide an extremely detailed view of the nuclear regions in this archetypal object and allow us to derive important constraints for theoretical models describing the launching of relativistic jets. A pixel-based analysis of the jet outflow, which still appears two-sided on the scales probed, was performed. By fitting Gaussian functions to the transverse intensity profiles, we could determine the jet width in the nuclear region. The base of the jets appears wide. The minimum measured transverse width of ${\sim} (227\pm98)$ $R_{\bf S}$ is significantly larger than the radius of the Innermost Stable Circular Orbit, suggesting that the outer accretion disk is contributing to the jet launching. The existence of a faster and Doppler de-boosted inner section, powered either from the rotation of the inner regions of the accretion disk or by the spinning black hole, is suggested by the kinematic properties and by the observed limb brightening of the flow.