RadioAstron reveals a spine-sheath jet structure in 3C 273

TL;DR

RadioAstron observations of 3C 273 reveal a complex spine-sheath jet structure with limb-brightening and central emission, suggesting stratification in electron energy distribution across the jet.

Contribution

First high-resolution Space-VLBI imaging of 3C 273 showing detailed spine-sheath jet structure at multiple frequencies.

Findings

Detected limb-brightening at 1.6 GHz indicating a sheath structure.

Observed central plasma emission at 4.8 GHz suggesting a spine component.

Revealed frequency-dependent jet morphology requiring stratified electron energy distribution.

Abstract

We present Space-VLBI RadioAstron observations at 1.6 GHz and 4.8 GHz of the flat spectrum radio quasar 3C 273, with detections on baselines up to 4.5 and 3.3 Earth Diameters, respectively. Achieving the best angular resolution at 1.6 GHz to date, we have imaged limb-brightening in the jet, not previously detected in this source. In contrast, at 4.8 GHz, we detected emission from a central stream of plasma, with a spatial distribution complementary to the limb-brightened emission, indicating an origin in the spine of the jet. While a stratification across the jet width in the flow density, internal energy, magnetic field, or bulk flow velocity are usually invoked to explain the limb-brightening, the different jet structure detected at the two frequencies probably requires a stratification in the emitting electron energy distribution. Future dedicated numerical simulations will allow the determination of which combination of physical parameters are needed to reproduce the spine/sheath structure observed by Space-VLBI with RadioAstron in 3C 273