Radio Images inside Highly Magnetized Jet Funnels Based on Semi-Analytic GRMHD Models

TL;DR

This study uses semi-analytic GRMHD models to simulate radio images of highly magnetized relativistic jets, revealing ring structures and features consistent with observations of M87, and highlights the influence of black hole spin on jet morphology.

Contribution

It introduces a semi-analytic GRMHD model to predict radio images of jet funnels, emphasizing the role of black hole spin in jet morphology and light bending effects.

Findings

Multiple ring images at 230 GHz for nearly pole-on observers.

Ring diameter of ~60 μas matches M87 observations.

Higher black hole spin results in thinner, smaller rings.

Abstract

By performing general relativistic radiative transfer calculations, we show the radio images of relativistic jets including highly magnetized regions inside jet funnels, based on steady, axisymmetric, and semi-analytic general relativistic magnetohydrodynamics models. It is found that multiple ring images appear at the photon frequency of 230 GHz for nearly pole-on observers, because of the strong light bending effect on photons generated at the separation surfaces which is the boundary between the inflow and outflow flows in the jet funnel. A bright teardrop-shaped component, which extends from the bright rings of the separation surface, also appears in the counter jet region. The diameter of the brightest outermost ring originated from the counter jet is $\sim 60 ~ \mu {\rm as}$, which is consistent with the ring-like images of M87 at 86 GHz observed with GMVA, ALMA and GLT, whose ring-diameter is $\sim 64^{+4}_{-8} ~\mu {\rm as}$. The thinner and smaller-diameter rings are exhibited when the black-hole spin magnitude is higher. These morphological features are expected to appear without being prominently affected by the detailed MHD-plasma parameters of our GRMHD jet model, since the location of the separation surfaces is mainly regulated by the black hole spin. Our GRMHD model and the emission features of the images in the horizon-scale, highly magnetized jet funnel may be tested by future observations, e.g., the next-generation Event Horizon Telescope and the Black Hole Explorer.