A Jet-Bases Emission Model of the EHT 2017 Image of M87*

TL;DR

This study models the emission from plasma rings at the jet base of M87 using general relativistic ray-tracing, suggesting that future EHT observations could reveal details about jet formation mechanisms.

Contribution

It introduces a jet-base emission model based on stagnation rings, providing new insights into the origin of the M87 ring image observed by EHT.

Findings

The model reproduces the M87 ring image observed by EHT.

The ring image contains features of jet bases beyond the photon ring.

Future EHT observations can resolve stagnation-ring structures.

Abstract

We carry out general relativistic ray-tracing radiative-transfer calculations to study whether a localized emission from $e^{\pm}$ plasma rings created at the stagnation surface in the jet funnel, to which we refer as stagnation rings, can explain the ring image of M87 observed by Event Horizon Telescope (EHT) 2017. The resultant images consist of the direct image of the stagnation rings and the ring images formed via the strong deflection by the black-hole (BH) gravity, to which we refer as "quasi photon-ring". For the model with the BH spin $a_* = 0.99$, the direct image of the counter-jet and quasi photon-ring are almost coincident to the photon ring with diameter $\sim 40 \mu{\rm as}$, while the approaching jet shows the small ring-image inside them. The synthetic observation image assuming the EHT 2017 array is consistent with that observed in M87, because the array is a bit sparse to detect the inner ring image. This indicates that the ring image in M87 might contain the important feature of the jet bases in addition to the photon ring. We find that forthcoming EHT observations can resolve the stagnation-ring image and may enable us to explore the plasma-injection mechanism into the jet funnel.