Did the Event Horizon Telescope Detect the Base of the Sub-Milliarsecond Tubular Jet in M\,87?

TL;DR

This paper analyzes high-resolution VLBA data of M87 to estimate the jet's properties, demonstrating a magnetically dominated, protonic jet solution consistent with observed polarization and flux, constraining the central engine's characteristics.

Contribution

It presents a detailed magnetohydrodynamic model of the M87 jet based on VLBA observations, linking jet properties to the central engine and polarization patterns.

Findings

Jet is protonic and magnetically dominated.

Estimated mass and energy fluxes constrain the central engine.

Polarization pattern consistent with a Parker spiral magnetic field.

Abstract

A high sensitivity, 7mm Very Long Baseline Array image of M\,87 was previously analyzed in order to estimate the bulk flow jet velocity between 0.4 and 0.65 mas from the point of origin using the asymmetry between the well-characterized double-ridged counter-jet (unique to this image) and the double ridged jet. We use this same image to estimate the cross-sectional area of this tubular stream. The velocity, acceleration, cross-sectional area and flux density along this stream determines a unique, perfect magnetohydrodynamic jet solution that satisfies, conservation of energy, angular momentum and mass (a monotonic conversion of Poynting flux to kinetic energy flux along the jet). The solution is protonic and magnetically dominated. The bilateral jet transports $\approx 1.2\times10^{-4} M_{\odot}/\rm{yr}$ and $\approx 1.1\times10^{42}$ erg/sec, placing strong constraints on the central engine. A Keplerian disk source that also produces the Event Horizon Telescope (EHT) annulus of emission can supply the energy and mass if the vertical magnetic field at the equator is $\sim 1-3.5$ G (depending on location). A Parker spiral magnetic field, characteristic of a wind or jet, is consistent with the observed EHT polarization pattern. Even though there is no image of the jet connecting with the annulus, it is argued that these circumstances are not coincidental and the polarized portion of the EHT emission is mainly jet emission in the top layers of the disk that is diluted by emission from an underlying turbulent disk. This is a contributing factor to the relatively low polarization levels that were detected.