Features of Structure and Absorption in the Jet-Launching Region of M87

TL;DR

This study uses multi-frequency VLBA observations to analyze the structure and absorption features of M87's jet-launching region, revealing non-uniform external medium effects and potential instability influences.

Contribution

It provides the most detailed spectral-index maps of M87's jet and links jet collimation with external medium density, highlighting the role of external absorption and instabilities.

Findings

External medium is non-uniform and influences free-free absorption.

Jet collimation correlates with local external medium density enhancements.

Jet morphology may be affected by short-lived kink instabilities.

Abstract

M87 is one of the best available source for studying the AGN jet-launching region. To enrich our knowledge of this region, with quasi-simultaneous observations using VLBA at 22, 43 and 86 GHz, we capture the images of the radio jet in M87 on a scale within several thousand R s . Based on the images, we analyze the transverse jet structure and obtain the most accurate spectral-index maps of the jet in M87 so far, then for the first time, we compare the results of the two analyses and find a spatial association between the jet collimations and the local enhancement of the density of external medium in the jet-launching region. We also find the external medium is not uniform, and greatly contributes to the free-free absorption in this region. In addition, we find for the jet in M87, its temporal morphology in the launching region may be largely affected by the local, short-lived kink instability growing in itself.