Resolving the inner parsec of the blazar J1924-2914 with the Event Horizon Telescope

TL;DR

This paper presents the first high-resolution, multi-frequency imaging of the blazar J1924-2914 with the Event Horizon Telescope, revealing jet bending and ordered magnetic fields at unprecedented 20 microarcsecond resolution.

Contribution

It provides the first total and polarized intensity images of J1924-2914 at 20 microarcsecond resolution, combining multi-frequency data to study jet morphology and magnetic fields.

Findings

Jet exhibits a 90-degree bending from 2.3 to 230 GHz.

Evidence for ordered toroidal magnetic fields in the core.

Multi-frequency images reveal jet structure from subparsec to 100 parsecs.

Abstract

The blazar J1924-2914 is a primary Event Horizon Telescope (EHT) calibrator for the Galactic Center's black hole Sagittarius A*. Here we present the first total and linearly polarized intensity images of this source obtained with the unprecedented 20 $\mu$as resolution of the EHT. J1924-2914 is a very compact flat-spectrum radio source with strong optical variability and polarization. In April 2017 the source was observed quasi-simultaneously with the EHT (April 5-11), the Global Millimeter VLBI Array (April 3), and the Very Long Baseline Array (April 28), giving a novel view of the source at four observing frequencies, 230, 86, 8.7, and 2.3 GHz. These observations probe jet properties from the subparsec to 100-parsec scales. We combine the multi-frequency images of J1924-2914 to study the source morphology. We find that the jet exhibits a characteristic bending, with a gradual clockwise rotation of the jet projected position angle of about 90 degrees between 2.3 and 230 GHz. Linearly polarized intensity images of J1924-2914 with the extremely fine resolution of the EHT provide evidence for ordered toroidal magnetic fields in the blazar compact core.