Pinpointing the jet apex in 3C 84

TL;DR

This study precisely locates the jet apex in the radio galaxy 3C 84 using high-resolution VLBI observations, revealing a spectral index gradient and estimating magnetic field strength near the core, advancing understanding of jet launching mechanisms.

Contribution

The paper introduces a novel method to pinpoint the jet apex in 3C 84 and provides high-resolution spectral index maps and magnetic field estimates, contributing new observational insights.

Findings

Jet apex located 83±7 microarcseconds upstream of the 86 GHz core.

First high-resolution spectral index gradient observed in 43-86 GHz pair.

Magnetic field strength estimated at 70-600 Gauss near the core.

Abstract

Jets which are powered by an AGN are a crucial element in the study of their central black holes (BH) and their immediate surroundings. The formation of such jets is the subject of intense research, mainly based on the dichotomy presented by the two main jet launching scenarios $-$ the one from Blandford & Payne (1982), and the one from Blandford & Znajek (1977). In this work we study the prominent and nearby radio galaxy 3C 84 (NGC 1275) with 15, 43, and 86 GHz quasi-simultaneous VLBI observations. From these we determine the jet apex to be located $83\pm7\,\mu$as ($0.028-0.11$pc) upstream of the 86 GHz VLBI core, applying a two dimensional cross-correlation analysis. A byproduct of this analysis are spectral index maps, in which we identify a robust spectral index gradient in the north-south direction, for the first time at such high resolution, for the 43-86 GHz pair. The magnetic field strength at distances from the VLBI core comparable to measurements from the literature ($\sim10$ Schwarzschild radii) for other prominent AGN, like NGC 1052 and M 87, is computed to be $70-600$G. Implications for the magnetic field topology are also discussed.